What are the differences in terms of appearance between sandstone and limestone?

The main difference is micro-texture. You cannot differentiate between both from a picture or a view, you need to go to the field and:

Break the rock with your hammer to observe
the rock in fresh-cut.
Add a bit of water to remove dust and correctly observe the colour and texture of the rock.
Finally use a magnifying glass to determine what the rock is made
of.

You should differentiate them as sandstones are always composed of grains. The texture is always grain-supported.

Limestones are composed of calcite. The texture use to be different, but it migth have also carbonated grains.

Rebooted Dunham classification of carbonates. Image from: commons.wikimedia.org

You can differentiate them in all cases unless you have a grainstone limestone with sand-grade grains (63μm-2mm). Then you need to identify the carbonated grains that can be fossils or oolites.

Oolites. Image from: commons.wikimedia.org

Fossils are clearly differenciated from sandstone grains with a magnifying glass, and oolites have a concentrical structure as shown in the picture.

Alternatively you can use dissolved hydrochloric acid or vinegar. As limestones are composed by calcite you will see a reaction, but you could also see the reaction on a sandstone if it has carbonated components.

Once you have determined the composition of a rock bed you can do the cartography at the lab with a stereoscope and aerial pictures or do it at the field again painting the limits on your map.


The speed of rotation of Earth is controlled by its angular momentum. And the conservation of angular momentum is a very serious law of physics (perhaps even stricter than conservation of mass). So in the same way that for the Earth to lose mass, that mass have to go somewhere. For the Earth to lose angular momentum, it'd have to go somewhere.

Earth's rotation can vary within a small range by rearranging the distribution of mass (changing the Moment of inertia). That's why on ice ages the day was a few seconds longer, because large amounts of water that used to be on the ocean was piled in large ice sheets, so like in the classic example of a rotating ice skater, by moving mass (ice on Earth or the arms of the skater) away from the rotation axis, slows down the rotation speed.

The only other way for the Earth to significantly change its rotation speed is by losing angular momentum, and any imaginable event that could change significantly Earth's angular momentum over a period of 15 years would be so catastrophic that the change in rotation speed would be secondary. Such event would have to be something like the collision with a massive asteroid, the fly-by of planet-size celestial body, or the ejection of large amounts of mass by the explosion of gigantic natural nuclear reactors (all things that might have happened very early in Earth's history).

There are however processes at work today that are slowly stealing Earth's angular momentum. The most important one is tides. Tides produce bulges of water around Earth that rotate slower than Earth, as in this picture (from Wikipedia):

Therefore, to keep the bulges in place the water have to be constantly flowing into those bulges moving against Earth's rotation and slowing it down by friction. The lost angular momentum goes mostly to the moon that accelerate on its orbit, therefore moving away from us 3.8 centimeters per year.

This process makes the day longer 1.7 milliseconds per century, something that is not a lot even at geological times scales. It is equivalent to 17 seconds per million of years. But even that small amount adds up to almost one full hour since the start of the Jurassic (201 Ma ago). But the change is so slow that animals would have plenty of time to adapt.

So I would say that any explanation of how the dinosaurs supported their own weight have nothing to do with changes in Earth rotation speed. Also, I think you are overestimating the impact of the rotation speed on the perceived weight. If we make the numbers, the centripetal acceleration due to rotation at the equator is
$$a_\mathrm c=\frac{v^2}r=\frac{(462\ \mathrm{m/s})^2}{6\,378\,100\ \mathrm m}=0.0336\ \mathrm{m/s^2}$$

Equivalent to a 0.3% of the acceleration of gravity. Therefore, even if the Earth were to stop completely, a dinosaur of 1000 kg would feel only ~3 kg heavier.

Said that, if we go to the very hypothetical case you say, a slow down wouldn't make much of a difference (ignoring any environmental impacts of having a one-year-long day).

And for how fast the can Earth spin and support life? I think nobody can really answer that question, as we don't know what conditions life can endure. But if you make the Earth spin faster, the centripetal acceleration grows as the speed squared, therefore it wouldn't take too much to make the centripetal acceleration equal to the acceleration of gravity, in which case objects in the equator would be weightless. In that case, Earth would lose its atmosphere and oceans, and further speed-up would start ejecting rocks into space. By rearranging the above equation we can get that critical speed, and it would be:
$$v_\mathrm c=\sqrt{rg}=\sqrt{6\,378\,100\mathrm m\times9.8\ \mathrm{m/s^2}}=7\,906\ \mathrm{m/s}$$

That is 17 times the current speed, equivalent to a day of one hour and 24 minutes.

Finally, for your  question: What is the fastest the Earth has ever spun? It depends. If we consider it after the main change in angular momentum associated to the formation of the Moon 4.51 billion years ago, we can just extrapolate those 17 seconds per million years (this is not the most precise as there were no oceans then, but it is a fair first approximation), and we get about 21 hours, so that the day at that time was only about three hours long.
Careful calculations for the length of the day in the proto-Earth before the formation of the moon lead to a day of 5.8 hours (see this paper, line 358)

As an anecdotal note, the fact that this number is quite close to the critical velocity, have made some people think that the explosion of a natural nuclear reactor could have been enough to give the extra kick to eject the whole Moon from the surface. Something that would explain why the composition of the Moon is so remarkably similar to that of Earth by recent analysis, challenging the theory of formation by a collision with "Theia" a hypothetical Mars-sized body. Although, there are other recent theories with an alternative solution to this problem, such as the synestia theory.

Finally, it would be wrong to restrict all possible changes of rotation speed only to surface processes or interactions to other celestial bodies. It could also be possible that mass redistribution in the Earth's interior could affect rotation speed. Events like the iron catastrophe would have increased the rotation speed, and other mass redistribution events could have happened or might be happening, but this is just speculation. Studying such processes is extremely difficult, we know very little about the dynamics of the Earth interior, and it will be extremely hard to prove or falsify theories concerning such internal mass redistribution events. This answers and and others in the same question have some ideas of how the angular velocity of a planet could change.


Could Global Climate Change increase the average moisture in the air?

Out of the total water on Earth, only a tiny fraction is held in the atmosphere at any given time.  Therefore, the direct effect of melting land or sea ice will not result in an increase in specific humidity.

However, warm air can contain more water than cold air, according to the Clausius-Clapeyron equation.  Therefore, the climate warming that causes the ice caps to melt, will also result in an increase in average specific humidity.  This is (approximately) an exponential relation (I don't have access to my textbooks right now, but googling saturation vapour pressure water equation yields many forms; I do not include them here because none I found use SI units).

Saturation vapour pressure of water.  Source: Chemguide.

See also the (not very good) Wikipedia article on Vapour pressure of water.


Do discordants dykes ever travel concordantly (are transgressive dykes a thing)?

Yes, they are. It's not the sills or dykes that "jump", it's the magma. Depending on the various parameters such as viscosity, stress, temperature, pressure, and local conditions and availability of joints, the magma will flow either as a sill or a dyke (or some other intrusive body).

Notice that your two sketches are basically the same thing - it's just the in one case the sill is the dominant structure whereas the dyke is more dominant in the second sketch.

The flow regime can definitely change from a "dyke" to a "sill" and vice versa. Here's a schematic diagram:

 (source: USGS)

I also had a quick Internet search and came up with this great example from nature:

You can read more about it at Geotripper blog by Garry Hayes.


Why do rivers sometimes travel down the opposite side of the mountains from where the rain happens?

In that image you have displayed you are assuming a 2D flow i.e. in the x and z direction where is x is the direction along the mountain range  which is parallel to the ocean(or sea) and the z is the vertical direction. This is a very simplistic assumption of mountain topography as depending on the context one can have mountain gaps and then the moisture laden winds can assume a 3D flow i.e. in the x,y,z direction( y in this case would be across the mountain). In the specific case you mention namely the Western Ghats there is the famous Palakkad Gap which bring in moisture laden winds from the Arabian Sea into rain shadow area(at least from the perspective of the South West Monsoon) and can fill up the river headwater source on the rain shadow region and these rivers then flow from west to east.

Secondly the atmosphere is a continuously stratified fluid and in the orographic context one needs to consider what is called the Froude number. From a layman's perspective this is a ratio between the inertial forces and gravitational forces that determine the 3D state of the atmosphere.
From a perspective of the the atmospheric scientist the inertial forces in this case would be horizontal wind field(monsoonal wind) and the gravitational forces are represented by Brunt Vaisala frequency and is a angular frequency that tells you how air parcels oscillate vertically in a stratified environment.

So assuming the following
              $$ Fr_n < 1 $$
what this means the incoming wind from the ocean side is not strong enough the penetrate the mountain barrier and you can have what is called upstream blocking. Often during the monsoon the monsoon trough will spend most of it's time offshore and only give skeletal rainfall to the coastal areas.

In the other scenario where the following applies

$$ Fr_n > 1 $$
in this case the wind is strong enough to penetrate the mountain barrier and the capping inversion on the Lee side can be broken in many ways(diurnal sensible heating and latent heating and ample moisture) can cause dark cumulonimbus clouds to form on the Lee side and that would certain fill up the river source on the Lee side as well.

As a case study Tamil Nadu which is not often a beneficiary of the South West Monsoon and is a rain shadow zone has had a surplus rainfall for the past two  years thanks to the principle explained above. The Thamirabharani river feeds off the South West Monsoon as it originates from the Pothigai Hills on the eastern side of the Western Ghats.

This paper - Houze 2012 Orographic Precipitation  is comprehensive and the specific case of the OP will be covered in figure 3e/3f as well as Figure 30(unblocked flow).


As always: It Depends.

Assuming enough water and sunshine, crop growth rate boils down to the concept of limiting nutrients. These may be: nitrogen (via ammonia or nitrates), phosphorous (via phosphates), potassium, and sometimes others.  In typical continental settings (i.e. subduction related vulcanism), lavas may be enriched in potassium and phosphorous but not nitrogen. So there will be some effect from rock composition.

Perhaps more important, there will be a refresh effect. If we have regular ash falls, this will 'top up' the soil as compared to normal soils, replacing nutrients. This is a similar effect to flood plains.

So, to answer, it tends to be true that volcanic eruptions increase fertility, but the most effective kind are from explosive ash-fall vucanism you get in regions like Italy or the US Cascades. The kind of flood-plain basalts you get in Iceland probably don't help.


What keeps water from sinking into earth?

So what prevents that happening on earth?

Not much. Quite a lot of water is recycled into the Earth's crust and mantle.

So the only thing that prevents the water from sinking in is the temperature, right?

That's part of the story. For our discussion, water can exist in two forms:

Molecular water as H2O, being in one of several phases (liquid water, solid ice, supercritical fluid, water vapour),
Structural water in solid minerals. For example, in clay minerals aka mud. Kaolinite is one of the minerals that make up mud (or dust) and has the formula Al2Si2O5(OH)4. See that (OH)4 in there? That's basically water. Even if you take a pile of mud, dry it at 110 °C in an oven until it's completely dry, the water is still going to be in there.

Molecular water can react with rocks and minerals to form hydrous minerals and get trapped as structural water (similar to adding water to Portland cement in the making of concrete), and hydrous minerals can be heated enough to release this water (usually requiring hundreds of degrees).
Let's look at some examples of how this thing might work.
Oceans have mid ocean ridges, where the oceanic lithosphere is being formed. This area has very shallow magma chambers so the rock is extremely hot. Water that percolates down through cracks gets heated to a large degree, lowering the density and increasing the buoyancy of the water. This water then goes back up through hydrothermal vents on the seafloor. Here's a spectacular video of some of those things:
https://www.youtube.com/watch?v=rTR6gGDWcJk
When the water goes down, not all of it goes back up. It also reacts with the rock, forming hydrous minerals. For example, anorthite (CaAl2Si2O8), a common mineral in basalts, is hydrated to epidote-clinozoisite: Ca2Al3Si3O12(OH). In some occasions, oceanic crust can be uplifted and is then exposed. One example is Cyprus, where you can see features like this:

What you're looking at is basically anhydrous rocks (the white stuff) replaced by hydrous minerals (the brown stuff) due to upwelling hot water in the oceanic crust. Above it, now gone, was a hydrothermal vent like the ones in the video.
On land, water does sink deep down as well. As Gordon mentioned in his answer, water is common in oil reservoirs, but it's just about anywhere else. It is particularly rich in sedimentary rocks, that still have some amount of the liquid water that existed during sediment deposition (river, lagoon, lake, etc).
A good property of water in subsurface conditions, is that at higher temperature and pressure it can dissolve and leach metals from rock. This provides a way to move metals around, eventually depositing these metals in localised locations so we can exploit them. Lead, zinc and gold are examples of metals that can be concentrated by circulating water.
Water can also go deep down into the mantle in subduction zones. Water trapped in pore spaces and hydrous minerals can sink hundreds of kilometres down into the Earth. Eventually, the temperature becomes too hot to sustain the water in there and the rock devolatilise: they lose the water (which is a supercritical fluid at this stage). This water is then incorporated into magmas, and erupted in volcanoes. In many volcanoes, especially in arc volcanoes (such as the ones around the Pacific ocean), a major component of "volcanic gas" is actually water vapour.
To sum it up, water goes down, water goes up. It's all one huge happy cycle.


What, if any, paleoclimate data can be derived from igneous rocks?

Stable isotope signatures in igneous rock (primarily $\delta$18O) can be affected by climate, but the effect is complicated and unreliable enough that I doubt it can really be used to say much about palaeoclimate. You might be interested in my friend Lara Owens' dissertation in which she considers the influence of climate on $\delta$18O in lava from Mt Erebus, Antarctica. Oxygen isotopes in Erebus precipitation are some of the lightest in the world, and she suggests that this water, after incorporation into a hydrothermal system whose rocks were later assimilated into magma, caused the anomalous $\delta$18O in some of the samples.

It would be interesting to see if there is a global geographic trend in similar anomalies, but I haven't heard of anyone trying that.

A more direct way that igneous rocks can record paleoclimate is through the effects that the atmosphere can have on pyroclastic deposits. Isopleth maps often can reveal the direction the wind was blowing during the eruption. Clast morphologies might even tell you the weather -- I'm thinking of accretionary lapilli, which form when an ash-rich eruption plume encounters a rain storm.

In conclusion, you might be able to glean a few data points here and there, but nothing comparable to the amazing records available in sedimentary rocks.

Edit to add: I just went to a lecture by Jay Quade about figuring out the timing of uplift in the Andes, and whether it came before or after the Atacama became hyperarid. Among many other geochemical tools, he used $\delta$2H in hydration waters on tephra, primarily to figure out palaeoaltitudes. He said he thinks the relationship between $\delta$2H and altitude has been fairly constant over the period of investigation (back to 50 mya).

Edit to add: I had forgotten to point out that subglacial eruption deposits are often distinctive (tuyas, hyaloclastites, pillow basalts). Wherever these deposits are found, you know a glacier or ice sheet was present and if you can date the rock then you know when there was a glacier there. Some recent work has suggested that you can even figure out the thickness of the glacier using the concentration of dissolved gasses in melt inclusions in the subglacially erupted lava flow.


What are the geological mechanisms for sea floor spreading in the Bismarck Sea?

Ah yes, this is a very good question. The formation of back-arc spreading centers is an open research problem, and happens to be the main topic of my office mate's dissertation! While these aren't exactly "clean" back-arcs, the formation of them is similar, I'm fairly sure.

The formation of back-arcs is caused by "Trench Roll-back". Trench Rollback is where the trench is pushed back in the opposite direction of the subducting slab and causes extension in the back-arc, forming a spreading center.  Below is a diagram from Modeling the dynamics of Subducting Slabs, Magali Billen, Annual Reviews of Earth and Planetary Sciences, 2008:

You can ignore the "Shallow" vs "Deep and Wide Box" comparisons, those only matter for building a modeling domain. What is important is noticing what happens to the slab when it hits the 660km boundary: it has a much more difficult time subducting. The slab "glides" through the upper mantle, but deeper in the earth, the mineralogical phase changes make the mantle much denser, creating a much stronger normal force on the slab. This normal force transfers energy into the slab and "pushes" back causing a drag between the deeper slab and the slab in the upper mantle. Since the under-riding plate and the overriding plate are weakly coupled viscously, only a small portion of the overriding plate is pulled with the trench. This causes extension/rifting.

Not all subduction zones have a back arc: weaker slabs tend to have a much harder time forming one as the transfer of energy in a strong slab is much more efficient.

It is also important to note that these phase changes are currently the leading theory, but our dynamic models have a hard time dynamically developing trench rollback. Sure, the literature might sound optimistic about it, but thats with surface kinematic boundary conditions and not pure dynamics.

These rifting centers form from trench roll-back. We can measure this roll-back with GPS. What causes trench roll-back is a much harder question to answer, in my opinion.


Is it possible to know what was the flow direction in a pegmatite dike?

I am not sure those are pegmatites. They may simply be granitic dikes. But in either case, you would need to assess the regional geology to look for potential sources of this material, which would be a granitic type magma of younger age than the host rock. You could then map out the size, orientation, and frequency of these dikes to tie them back into their parent unit. Geochemical fingerprinting and age dating could help, too. But there is no way to look at that picture, or a given outcrop, and tell the direction. Remember that the geometry of the third dimension, the one in and out of the picture or outcrop, always needs to be kept in mind and is typically unknown.

I am pretty sure it was not top down, though!


What causes these odd-looking currents in the Tasman Sea?

Great question. These features are mesoscale Eddies and they are akin to hurricanes in the atmosphere. They are the ocean’s high or low pressure systems and are the result of instabilities. The cyclonic eddy (counterclockwise direction in the northern hemisphere) is called a cold-core eddy and the anti-cyclonic eddy is called a warm-core eddy.

Unlike destructive hurricanes, ocean eddies are important physical processes for the transport of heat and particulate matter. They stir up the ocean drawing up nutrients from the lower depths and fertilizing waters as they propagate. They are important for the transport of marine organisms in the offshore direction and support phytoplankton and zooplankton production.

In the Tasman sea, this region is known as 'Eddy Avenue' which speaks to their ubiquity and persistence. In Everett (2012) they identified 30 thousand eddies in a period of $15$ years.

  ... at a density of 61 cyclonic and 63 anticyclonic eddies per $10,000$
  km$^2$. On any given day there are 16.8 cyclonic and 17.8 anticyclonic
  eddies within the Tasman Sea. Tasman Sea eddies are typically smaller
  than the global average ($82$ km radii compared with $86$ km), have a
  faster rotational speed ($23$ cm s$^{-1}$ compared with $15–16$ cm
  s$^{-1}$) and have a larger Sea Level Anomaly($10$ cm compared with
  $6–7$ cm) (Table 1).

Generation:

  “When the current separates from the coast, it gets complicated. It
  starts to wobble; it meanders. Rather than going in a relatively
  straight path like the Gulf Stream in the North Atlantic, it walks
  like a drunk man.” Not only does the EAC wobble, it U-turns. [...] The EAC is a bit  anomalous.” About two-thirds of the current retroflects back up into
  the eastern Pacific, breaking up the EAC further. “It really is a
  current of eddies.” Such instabilities saturate Eddy Avenue with
  eddies.

As far as the El-Niño connection, I can only speculate. But generally, El-Niño will give rise to positive SST anomalies. The figure below shows recent positive SST anomalies which are relatively strong near the coast. Because ocean temperatures are higher ocean eddies can increase in size and strength.

References

Everett, J. D., M. E. Baird, P. R. Oke, and I. M. Suthers. 2012. An avenue of eddies: Quantifying the biophysical properties of mesoscale eddies in the Tasman Sea. Geophysical Research Letters 39, L16608, doi:10.1029/2012GL053091.


Does subduction of continental crust happen at continental-continental convergent boundaries?

Both of the processes you describe occur; in some cases such as the Himalayas the plates are not subducted and a moving plate, in this case the Indian plate, bulldozes the continental crust ahead of it into a high mountain range. In most cases, such as the Pacific rim for example, subduction is the norm. Where there is subduction there are usually many volcanoes, and this is certainly the case on the Pacific rim. The subducted crust carries rock and water down into the hot mantle, where the friction,heat and water content tend to liquefy it,and it rises to the surface to form volcanoes. To answer your specific question, no. there is no subduction when continental crust meets continental crust, as is the case with the Indian plate meeting the Eurasian plate. Subduction occurs when sea floor spreading forces a plate underneath the lighter and more buoyant continental crust.


What would be the depth variation of a "water ellipsoid" above a reference ellipsoid Earth?

A complicating factor will be the change in density with temperature. So for this I will assume a constant density of water.
As the thickness of the water layer is quite small compared to the size of Earth (given as 2.6 km by the answer to the other question) I think an approximation with a constant g at any particular location should give a fairly reasonable answer.
Water naturally finds its level based upon pressure. So if we have a constant pressure at the top of the surface, the pressure at the bottom must also be constant. And this should work as a reasonable approximation for any number of layers.
Noting that for any column of water, the pressure increase will be given by:
$P=\rho \cdot g \cdot h$
Taking the values of g from Wikipedia:
At the equator, g, due to Earth being an oblate spheroid and rotating is ~$9.78 \frac{\mathrm{m}}{\mathrm{s}^2}$
At the poles, g is ~$9.83 \frac{\mathrm{m}}{\mathrm{s}^2}$
Equating the 2 we end up with:
$P=\rho \cdot 9.78 \frac{\mathrm{m}}{\mathrm{s}^2} \cdot h_e=\rho \cdot 9.83 \frac{\mathrm{m}}{\mathrm{s}^2} \cdot h_p$
Factoring out common terms leaves us with:
$h_e = \frac{9.83}{9.78} h_p$
So the equator will have water that is roughly 0.5% deeper than the poles.
For 2.6 km, that works out to be roughly 13 m.


Change in vertical wind intensity in atmospheric modeling

It really depends on whether you're model is hydrostatic or not.

If your model is hydrostatic, then the vertical velocity is found diagnostically. The diagnostic algorithm is called the Richardson Equation.

If your model is nonhydrostatic, often it is presumed that the vertical velocity is 0. The vertical velocity is presumed to be 0 (unless you do some spin-up or model restart, or some other special initialization), and the prognostic equation for vertical velocity is found.


Why doesn't Earth absorb our carbon emissions?

That assumption is indeed logical and correct, and increased plant growth is in fact happening (this effect is known as $\ce{CO2}$ fertilization). As you suggests, Earth will adapt to the increased inflow of $\ce{CO2}$, and it will find equilibrium again. What might be missing in your reasoning, is the fact that the atmospheric $\ce{CO2}$ concentration in the new steady state would not be the same as the concentration in the pre-industrial steady state.

The atmosphere is a reservoir of $\ce{CO2}$. Its has sources (volcanoes, plant respiration, decomposition, fossil fuels combustion, etc.) and sinks (photosintesys, ocean uptake, silicate weathering, etc.). To simplify the system let's do an analogy with a bath tub.

Let's imagine a bath tub with a very powerful faucet and a sink.
Now let's start opening the faucet until the sink becomes overwhelmed by the incoming water and the level in the bath tube starts to rise.
As the level rise, the water pressure at the bottom will rise too, therefore, more water will rush through the sink. Eventually the water going trough the sink will match the water coming in, and the water level will stabilize. At this point we have reached steady state.

If we open the faucet a bit more, the water level will rise again, up to a point where the bottom pressure allows the sink to catch up and a new steady state is reached, but this time at a higher water level. Also, note that after we increase the inflow of water, it takes some time to reach the new steady state, and that time depends on the sizes of sources and sinks relative to the reservoir. In our example, if the same faucet and sink were in an Olympic swimming pool instead of a bath tub, the time would have been much larger.

Going back to Earth, the atmospheric $\ce{CO2}$ concentration was pretty much as steady state before the industrial revolution (if we consider ~1000 years time scales). Then, with the industrial revolution we increased the inflow of $\ce{CO2}$ into the atmospheric reservoir. As a consequence, the ocean and erosion increased their $\ce{CO2}$ intake, and plats increased their photosynthesis rate. In that way Earth, as you correctly assumed is working its way back to a new equilibrium. However, to reach that equilibrium takes time, and once we reach it, the atmospheric $\ce{CO2}$ will be higher than the pre-industrial levels, and that will in turn lead to a stronger greenhouse effect, higher temperatures, and climate change.

It is also important to note, that the extra inflow of $\ce{CO2}$ didn't just increase at one point and stopped (like our faucet). It is constantly increasing to higher and higher levels of $\ce{CO2}$ production, making even harder for natural systems to bring Earth to a new equilibrium.

The first figure in the Wikipedia article you linked shows this neatly:

We can see here in white numbers the most significant pre-industrial sources and sinks (at ~1000 years time scales). We can see that humans produce 9 Gigatons of carbon per year (GtC/yr), due to that extra inflow, photosynthesis is taking 3 GtC/yr more than before, and the ocean is taking an extra 2 GtC/yr as well. However, that is not enough to counteract the 9 GtC/yr we produce, and that is increasing the amount of carbon in the atmosphere at 4 GtC/yr. This means the level in the atmospheric "bath tub" is still rising.

If we were to keep those 9 GtC/yr we produce stable (i.e. not increasing production in the future). The concentration of $\ce{CO2}$ in the atmosphere will rise to a level high enough that the sinks will match the sources, for example with plants taking 5 GtC/yr and the ocean 4 GtC/yr, that would nicely balance the production. But that new equilibrium atmospheric $\ce{CO2}$ concentration would be high enough to rise Earth's temperature several degrees and force a whole reorganization of the Earth's climates.

Finally, we have to say that some of these $\ce{CO2}$ intakes, like the oceanic one, don't come for free, and have their own nasty consequences, like ocean acidification.


Feedback loops between soil chemistry and plant growth

You're on the right track, though the positive and negative aspect of feedback loops is more about dynamics of the overall system rather than just the increase or decrease of components in the feedback loop. This website offers a straight forward explanation of positive vs. negative feedback loops https://serc.carleton.edu/introgeo/models/loops.html :

  Feedback Loops can enhance or buffer changes that occur in a system.

  Positive feedback loops enhance or amplify changes; this tends to move a system away from its equilibrium state and make it more
  unstable.
  Negative feedbacks tend to dampen or buffer changes; this tends to hold a system to some equilibrium state making it more stable.

In your second example, the feedback loop between temperature and soil organic matter leads to amplified changes in the system, making it more unstable. You're correct in identifying this as a positive feedback loop.

In the first example about plant available nitrogen and plant growth, there is a feedback loop there but is it positive or negative? You noted that the effect of increased plant growth would reduce available nitrogen. That isn't necessary the case, but even if it was, reduced nitrogen itself could actually be a positive feedback loop because it would lead the system out of equilibrium and into an unstable state (with the plants present no longer able to sustain themselves). However, in an undisturbed ecosystem I'd expect this to actually increase available nitrogen and also increase stability of the system over time, making this a negative feedback loop.

The relationship between soil nutrients and plants can be complex and vary between plants (e.g. leguminous plants would certainly create a negative feedback loop, enhancing the stability of the system they are thriving in). In general plants left to their own succession would increase organic matter which serves as a nutrient reservoir, further enhancing nutrient availability. In our more controlled agricultural systems, you can see this effect applied in crop rotation and allowing fields to go fallow as a means to increase available nutrients among other potential benefits.

Note that the nature of a feedback loop also depends on how the system's boundaries are defined. This is especially true looking at industrial agriculture and other systems that rely heavily on external inputs or otherwise have far-removed externalities.


Is everything affecting everything on Earth?

Do you know what the weather will be in four hours time? You can probably make a very confident guess. How about this time tomorrow? You can probably make a reasonably confident guess. How about this time, in fourteen days exactly? Now, you're much less confident.

That's because weather is a chaotic system, and it's very sensitive to boundary conditions.  In such a system, very small disturbances can make very big changes, far enough out.

Now, for Wisconsin (as that's what the OP's profile gives as their location), let's think about the external air temperature at 05.00 on 1 February 2017, and at 14.00 on 1 July 2017. Which do you think will be higher? Will it be a difference of a few Kelvin, or more than ten Kelvin (18°F) difference? How confident are you in your answer? You're probably very very confident that the July temperature will be higher, by more than ten Kelvin. The climate is still reasonably predictable months or years ahead, even though it gets very hard to predict the weather reliably more than ten days ahead. Climate is a long-term system, and is not sensitive to boundary conditions in the same way that weather is.

If you roll a fair six-sided dice once, you can't be very confident about whether a one will come up, however much you know about the air movements in the room when you throw the dice (you can be reasonably sure that the probability is 1/6, however much you know about the air). However, if you roll that dice 6000 times, you can be reasonably confident that one will come up a thousand times, give or take a hundred times, and you don't need to know anything about the air movements in the room.

That's the difference between weather and climate; even though weather is just a manifestation of climate, it's just a sample from the climate distribution.

We've built the global economy, patterns of habitation and movement, food supplies, energy systems, around the climate that we've had for the last few hundred years. And that should be ok, because climate, sea levels and sea pH levels normally take between thousands and millions of years to change radically. But our releases of greenhouse gases are now causing big changes to happen within years to decades: and it will be enormously expensive, disruptive, and cause huge suffering to billions of people, to reorient the global economy, patterns of habitation and movement, food supplies, and energy systems, to newer, unknown, unfamiliar climates, coupled with rising sea levels and ocean acidification.


If US emissions went to zero how long until global emissions reach current levels

That will depend on the emission scenario you pick for the future, the more recent scenarios are the RCP's (Representative Concentration Pathway).

RCP scenarios

The scenarios involve future pathways in the emissions of a large range of different chemicals (Greenhouse gases and aerosols). Each RCP have a temperature tag, for example RCP6.0, is a scenario that consider many geopolitical, social and economical predictions and that would result in an emission pathway that would the radiative forcing (input energy to Earth) by 6.0 W/m$^2$ by year 2100.

The data associated with the RCPs can be accessed in the RCP Database, this is a plot generated there with Global $\text{CO}_2$ emissions for all four RCP scenarios.

According to this data, the U.S. was responsible for 14.34% of the global emissions of $\text{CO}_2$ on 2015.

If we consider that overnight all scenarios switch to a  version of themselves with a 14.34% emissions reductions (i.e. like if the US stopped all its emissions suddenly), the plot would look like this:

Where the dashed line is the new emission pathway and the thin dotted line marks the global emission level before the US $\text{CO}_2$ shutdown.

We can see that for RCP2.6 and RCP4.5, the world would never get back to emission rates as high as those of today. And for the more pessimistic scenarios it would take at least 10 years to go back to those levels: For RCP6.0 it would go back to current levels by 2041 and for RCP8.5 by 2029.

There are many simplifications on this calculation, but gives you a first approach. If you are interested in another emission scenario you can apply the same methodology or a better one, but maybe this can serve as a starting pint.


Classification of rivers according to width

The Rosgen river classification contains - besides slope, entrenchment and sinuosity - the width. But it is mostly applicable to natural rivers, not so much artificial waterways ...

http://extension.umass.edu/riversmart/fgm-assessment-methods/rosgen-classification-natural-rivers-natural-channel-design

https://en.wikipedia.org/wiki/Rosgen_Stream_Classification

https://content.ces.ncsu.edu/application-of-the-rosgen-stream-classification-to-north-carolina

https://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcs142p2_024290.pdf


Is global warming being moderated by latent heat of melting polar ice?

Latent heat is a factor, but is completely eclipsed by the rate of global warming.

For example, since 1978 the April (maximum) Arctic sea ice has decreased in volume by about $11,000$ cubic km. The latent heat absorbed by the ice to achieve this is about $3.7(10)^{18}$ Joules. Compare this to the amount of excess heat, which has been absorbed by the oceans, which is about $2.0(10)^{23}$ Joules per decade. That is, some three to four orders of magnitude more heat than the decadal heat required to melt the Arctic ice.

Of course there are complications of the heat absorbed by land (much less than in the oceans), melting of Greenland and Antarctic ice sheets, and uncertainty over the depth of oceanic warming, due to sparsity of measurements, especially in the southern hemisphere.

But however you cut the statistics, the latent heat is minuscule compared to the planetary heat imbalance.


Most volcanism occurs at three major tectonic features: Subduction Zones, Rifting Centers (Like East Pacific Rise) and under hotspots.

I will start with the most contentious, hotspots. The clearest example of hotspot volcanism is the island chain Hawaii. Underneath the island, there is a chaotic discontinuity caused by the boundary conditions at the core-mantle boundary. This causes highly viscous and hot mantle to upwell rapidly and push through the lithosphere, forming a volcano. The orgin of hotspots is not well known, and it is even a debate if they exist (they do, imo). Some papers worth looking at are by Paul Hall (BU) and Christopher Kincaid(URI), and maybe Dave Stegman (Scripps) who publish on melting caused by mantle plumes.

As a consequence of a subducting slab, at a distance in front of the trench, Arc Volcanoes form. The distance in front of the trench is often thought to be where the overriding plate is 100-120km higher than the suducting slab. The cold, oceanic plate plunges underneath the continental plate in the image above, adding water to the mantle. This water lowers the melting temperature (solidus) of the mantle inside the wedge of the subduction zone, causing  partial melting (4-6%). This melt, more viscous and buoyant than the solid mantle, floats to tho the top of the mantle and eventually penetrates the lithosphere and forms a volcano. This question is also relevant.

Finally, at divergent plate boundaries, the process is fairly straight forward. A break in the lithosphere caused by rifting plates allows the pressurized mantle to flow towards the opening. This causes and abundance of hot, fertile mantle which can be melted.  This melted mantle creeps through the lithosphere and forms ocean floor volcanoes (sometimes called smokers).


If all the world's ice were to melt, would this shift the earth's centre of gravity with consequential effects on sea levels?

As a prescript, your question is firmly within the field of Glacio-Isostatic Adjustment (GIA) modeling of the Earth and the sea level. The main scientific names doing research in this direction are Jerry Mitrovica, W.R. Peltier, Roblyn Kendall, Glenn Milne, Kurt Lambeck, Giorgio Spada, and probably some more that I'm forgetting. It all comes down to, basically, the 'Sea Level Equation' (SLE), https://en.wikipedia.org/wiki/Sea_level_equation .

Copying straight from Wikipedia, the simplest form of the sea level change $S$ is given by the difference between the shift in the geoid (i.e., the effects you describe) $N$ and the changes in vertical land positions ($U$):
$$ S = N-U .$$

It is this second factor, the response of the Earth and ocean bottom to the changing loads, that you didn't take into account, that can lead to some serious local deviations from the gravitational aspect alone.

See Figure 2-2 from http://skb.se/upload/publications/pdf/TR-09-11.pdf, copied here below:

Figure 2-2. (a) Ocean height is perturbed upwards due to the gravitational attraction of the ice sheet. Solid Earth is depressed downwards due to the mass of the ice sheet. (b) Local relative sea-level fall due to a decrease in gravitational attraction by the ice (red dashed line shows previous position), combined with solid Earth rebound (green line shows previous positions) due to the ice sheet having a smaller mass. Far-field sea-level rise is due to the addition of meltwater into the ocean. Adapted from Tamisiea et al. 2003.

After staring at this figure for a while, you may appreciate that, indeed, from state (a) to (b) as the ice cap melts, the far-field sea level rises through addition of fluid water and a drop in the gravitational attraction nearby. However, also, now that the ice cap is smaller and less heavy, the solid Earth responds by moving up! Hence, 'close' to the ice cap, the sea level doesn't drop as much as you would expect from amount of fluid water + gravity alone. NB: the same happens with the oceans: adding more water to the oceans depresses them, see page 26, figure 11 here https://arxiv.org/pdf/1212.5061.pdf  with the 'relative sea level change' around the Mediterranean Sea, compared to the present. Copied here below is one for 10 thousand years ago:

Apparently, the sea level has risen by 30 meters in the center of the sea, but only about 22 meters on the edges. The reason is that the Mediterranean sea, from 10 thousand years ago to today, gained more mass, which caused it to depress the sea bottom / Earth's crust in the center! Hence, it had to rise even more in the center (compared to the coast lines) to create a flat surface today.

The difficult thing is that these are non-local processes. You kind of need to know about such local Mediterranean changes to make an accurate prediction for the sea level in, e.g., the Gulf of Mexico or so, because it changes the center of mass and the fluid sea water budget that can be distributed!

So with respect to your question, I absolutely think you are right that gravity is an important aspect, and 40 meters relative sea level change differences due in the hemispheres are absolutely possible for the reason you mention. If the melting is instantaneous, this is the main aspect. However, if you wait a century or so, the Earth's deformations start to kick in, can play a serious role, and can dramatically affect the sea level distribution again, in not easily foreseeable ways!


How are subsurface wave speeds determined without subsurface sensors?

This is a good question, and the basic answer is earthquake seismology. To answer this question, lets accept a fact: Waves propagate through the least time pathway, and not the least distance path. This property of physics is known as Fermat's principle.

When an Earthquake occurs, energy propagates similar to a ripple of water, and spreads. Each point on this ripple can be modeled as a ray, each following its least time path through the Earth. As these rays propagate, they reflect and refract  off heterogeneities inside the earth. These reflections are important: we can detect these reflections using surface seismometers. Using multiple seismometers, and the location of the source (earthquake), we can calculate the "lag" between when the closest seismometer detects the earthquake and the others(further from the source). This lag time can be used as a proxy for the depth of the reflected wave's heterogeneity. Using how deep this reflection originates, we can then figure out the least time path of the wave in terms of actual distance. Velocity is just distance over time, even for seismic waves. So since we have the distance traveled by the wave, and the time the wave took to get to the receiver, we can complete the equation (distance/time).

In actual practice, this process is far more complex, as you have to look for many different waveforms:

The picture above illustrates an earthquake sending waveforms through the earth. The SKS wave is a shear wave that refracts into the liquid outer core, turns into a compressional wave (since shear waves cannot propagate through liquid), and then is converted again to a shear wave as it enters the mantle and goes to the surface. A trained seismologist looks at the readings from seismometers to tease out specific waves, which we know the properties of, to determine properties of the planet's interior. The speeds of these waves are highly dependent on the assumed densities and other rock properties of the crust, mantle, and core.


If a prevailing wind traveled due east in the Northern Hemisphere, would the Coriolis Effect act on the water?

The Coriolis Effect occurs in all directions equally, even straight zonal (east-west) winds.

Many indeed struggle with this idea - this Physics SE question has a fair explanation as to why.

As arkaia commented, the total deflection magnitude is $f=2{\omega}\cdot{\sin(latitude)}$, which is an orthogonal vector change (and as such shows up as terms in both the zonal and meridional velocity equations).

So there's still deflection to the right (in the NH) equally regardless of which direction the air/water is flowing (except that in such a feature, deeper water is moving slower, so deflects by less magnitude... but still matching in regards to the proportion in comparison to the velocity).  Otherwise the result would not be a spiral... but only at most a 90° decaying curve, since as the water begins to turn towards a more zonal direction, the angle of deflection would start to decrease, until at some height the water is moving easterly (or westerly) (such as at height labeled 3 in this diagram), and the water below it wouldn't turn further.  So the direction independence of Coriolis is vital to there being Ekman spirals at all.


What geological processes affect the speed of Kilauea lava flows?

The speed of the lava flow from Kilauea depends on a few things:

The amount of activity at the source of lava.  This flow you are talking about is coming from a vent that is 20 miles from the Kilauea caldera.  So, it is more like a leak, than a true eruption.  There's not a lot of force behind these types of events and thus not a lot of lava coming out.
The viscosity of the lava.  This is basalt, so it can move pretty quick, for lava.
The terrain.  The source of the lava is not near the summit, but rather far down the mountain at only 700 ft elevation.   The surrounding terrain has a very shallow slope, which doesn't allow the lava to move downhill quickly.
The cooling rate of the lava.  It rains a lot in Pahoa.  Especially in late October.  This helps to cool and harden the lava, which slows the movement.
Barriers and surface characteristics.  There are a lot of natural contours in the land, trees, and brush in the Pahoa area.  This helps to slow down the movement.

Having grown up on the Big Island, I can say from experience that these flows that come out of side vents are often slow enough to walk right up to and play with.  They don't move fast at all.  The reason it's such a big news event is because it nearly covered a main highway, which would've cut off a lot of people from the main town, Hilo.

The fast-moving lava flows usually come from the main caldera, where the amount of lava erupting is far greater.  Also, Kilauea is really just a pimple on the side of Mauna Loa.  So, it is a bit of a release valve for the big volcano.  Shouldn't be too long before Mauna Loa erupts again and then you will see a lot of fast moving lava from a 13,000+ ft location.


How to make wind forecast like Predictwind.com? Which mathematical model has been used?

It seems like that particular website is a commercial forecasting website and requires login/registration information, so I will take your word for the output.

The general equation of motion is described by the Navier-Stokes Equations, which is $$\frac{\partial \vec{u}}{\partial t}+(\vec{u} \cdot\nabla)\vec{u}=-\frac{1}{\rho}\nabla P+g\hat{k}+\nu \nabla^2\vec{u}+f\hat{k}\times\vec{u}$$ where $\vec{u}$ is the atmospheric motion vector (wind + vertical motion), $\rho$ is density, $P$ is pressure, $g$ is gravity, $f$ is the coriolis parameter, and $\nu$ is the kinematic viscosity.

This very complicated equation currently has no analytic solution (if you have one, you can win $1,000,000 from the Clay Mathematics Institute), but is instead discretized and solved using even heavier mathematics. Additionally, some mathematical tricks are played on the equations to 'simplify' them, but it usually results in other problems.

While 8 km seems like a fine scale, it actually isn't. Smaller phenomenon (called eddies) affect the weather significantly, so research that tries to mimic the effect of those eddies is applied, but there are still problems. Cutting edge research tries to reduce that 8 km (called resolution- think of the resolution of your television) down to tens of meters, but at a significant cost- one that limits the domain.

Likely, the data that your website comes from a weather model, which attempts to solve the above equation. Such models could include the ECMWF, GFS, and other global models.


What are the most common minerals at the Earth's surface?

I can't seem to find a good reference for the top few hundred minerals that actually occur in macroscopic quantities in near-surface rocks.

That's because such a list does not exist. The 'first few most common minerals' you mentioned, aka the 'rock-forming minerals' account for 99.9% (at least, depends on definition) of the minerals you will find in near-surface environments. It also depends on location - the minerals you will find in a limestone are will be completely different from the minerals in granitic areas.

I also don't completely seem to understand what you mean by 'macroscopic quantities'. Are you referring to minerals that are large enough to be seem by the naked eye or that are abundant in quantity regardless of their size?


Circular patterns at bottom of rock, is it a fossil?

The face of the rock with the round center portion looks strongly like a Rugosa or Horn Coral.  I suggest it is a Rugosa coral because of the center with the radial lines out from the center and the clear edge surrounding the radial lines.  See https://en.wikipedia.org/wiki/Rugosa.


How will increased $\ce{CO2}$ affect forests and other vegetative areas?

If you increase CO2 concentration and keep all other parameters at there current level, then biomass production should go up. The reason is simply that CO2 is one of the building blocks biomass is made of in photosynthesis.

In the real world it's trickier than that of course. Here you have to take into account how natural cycles will be affected by increased CO2 levels. Temperatures e.g. will go up which is expected to be beneficial for biomass production for moderate increases and becomes increasingly bad for higher increases. Precipitation patterns change, wind patterns and therefore soil erosion change etc. etc.

Chapter 7 of the IPCC report deals with the question how climate change affects biogeochemical cycles; biomass production is one of the parameters that go into the carbon cycle.

To my knowledge biomass production is one of the parameters that benefit from moderate temperature increase but are expected to turn to their opposite around the 2-degree benchmark.


There have been a few studies related to the effectiveness of sandbags in flood events, these are usually based on observations performed after flood events.  Overall, studies have shown that sandbags only have modest protection in its use as a domestic (1).

A major factor the research shows is that the maximum effectiveness occurs to about 1 metre depth (1), they can, on occasion, hold out in higher flood levels, but as Reeve and Badr (2) determined, leakage between the bags increases rapidly with increasing flood water levels.  However, due to the unique nature of each flood conditions, there is still a large degree of uncertainty as to what effectiveness actually means in terms of sandbags (1).  However, the major degree of effectiveness is highly dependent on the number of rows of sandbags and the duration of the flood (2).

Asides from floodwater height and duration, and height of sandbags, other factors that affect their effectiveness include:

Waves on the flood waters increase instability of sandbag walls/dikes, especially as floodwater depth increases (5).
Ambient conditions - temperature mainly, if low enough - ice could form between the bags decreasing their effectiveness (5).
Speed of flood waters - having eyewitnessing (and being caught in) a flash flood (3), fast moving water itself (and the debris it invariably contains) can severely degrade the effectiveness of sandbags.
The time taken to build the sandbag wall, as well as build up the height of the wall should the flood levels rise.

In reference to the comment about alternatives, one major alternative is preventative action, even though it is impossible to fully protect against floods, particularly large-scale and flash-flooding. After the 2002 floods of the Elbe River in Germany, it was found that household preventative measures lessen the damage from a large scale flood (4).  Related, flood minimalisation techniques are explored including soil bioengineering (6).

References

(1) Botzen et al. 2008 Willingness of Homeowners to Mitigate Climate Risk through
Insurance

(2) Reeve and Badr, 2003 Performance of sandbags for domestic flood defence, Proceedings of the ICE - Water and Maritime Engineering, Volume 156, Issue 4, 01

(3) Worst Queensland Floods In 35 Years 11/01/11 YouTube news clip

(4) Kreibich et al. 2005 Flood loss reduction of private households due to building precautionary measures -- lessons learned from the Elbe flood in August 2002 Natural Hazards and Earth System Science

(5) Raymond, 2009, Wave action and the effects of the environment on sandbag dike performance Thesis - University of Manitoba

(6) Dhital and Tang, 2015 Soil bioengineering application for flood hazard minimization in the foothills of Siwaliks, Nepal Ecological Engineering


What caused a centuries long freeze, the beginning of the current ice age. Yes we are in an ice age, as long as greenland and antarctica have large ice sheets we are technically in an ice age) Which in turn was caused by the movement of continents close enough to the poles to create permanent ice caps. the freezing of organic matter into permafrost is not a fast occurrence, it is a slow build up of organics as soil is built and added too, as long as it remains cold enough for permafrost to persist.

The strange thing about the warming now is every major natural factor and most minor factors point towards cooling conditions yet we have warming. Human activity however is producing strong warming factors that are overriding the natural prevailing conditions, which makes you wonder what will happen when some of the natural factors stary cycling back to warming.


How can I specifiy a substance in AERMOD?

The POLLUTID key is used to specify some regular options.
Some examples:

PM2.5 can only evaluate averages greater than 24 hours (if you try to generate hourly averages it throws an error).
NO2 forces the use of options to simulate the conversion of NOx to NO2.
SO2 triggers the use of a 4-hour half-life for SO2 decay in urban zones.

All pollutants (gases and particles) are treated similarly, regardless of their weight or molecular density.


Are weather forecast models more accurate for either high or low temperatures?

There are two ways to answer your question: the first would be by verifying historical forecast data (calculating the difference to observed temperatures) and looking into a temperature dependency of these errors. This would certainly be doable - but in this context on Stackexchange not.
So I suppose you refer to a general, more physically interpretable explanation what the difference in forecasting higher or lower temperatures is.
Even though it makes a difference for physical processes like radiation and evaporation if temperatures are high or low, the characteristics stay the same - more explicitly said:
Temperature differences matter more than absolute temperatures!
For example:

The net radiation (budget) is proportional to the difference of soil and atmospheric temperature (each to the fourth power).

Deeper layers of soil keep the surface warm by transporting heat (also proportional to the temperature difference).

and so on...

But there is a significant difference in the active physical processes:
At daytime (Tmax), the near surface air is (mostly) coupled to the temperature of higher layers of air by turbulence. On a sunny summerday, the surface air can not get significantly warmer than the air above because if it gets warmer, the air rises and cooler air from above cools the surface layer. In this way, the surface air temperature is 'tied down' so that it can not reach extrordinary temperatures without also heating up a say 1500 m boundary layer of air.
If the surface air is cooler than the air above it gets decoupled from the temperatures above - turbulence is reduced, and theoretically the temperatures could drop a looong way down, until the incoming (longwave) radiation from the atmosphere (say hi to greenhouse gases) stops this temperature drop. The equilibrium temperature depends mostly on the amount of water vapor above our heads -> warmer in the tropics, cooler nights in polar regions. But the equilibrium is practically never reached. In most cases it is a dynamic thing with  ground heat flux and sporadic wind gusts - which are of very local effect.
Conclusion
Comparing these two cases one can see that the Tmax is more homogenously distributed in space because it mostly depends on the airmass. Minimum temperatures can be very different even for close locations because it really depends on your surrounding: trees, buildings, ridges. You can see the lowest Tmin at high altitude locations which are not exposed to wind gusts (sinkholes) which are covered by snow (isolated from soil heat).
So by analyzing a forecast error dataset, you would most likely see that Tmax are more accurately forecast.


Studies shows there is Methane on Earth's Crust. The chemical form how it is stored is called Methane Clathrate,

"a solid clathrate compound (more specifically, a clathrate hydrate)
in which a large amount of methane is trapped within a crystal
structure of water, forming a solid similar to
ice."
(source:wikipedia).

There are two main origins for this structures on Earth's Crust, mainly developed at the Oceanic Crust and stored some centimeters or meters below the water interface, after the sulfate reduction zone:

Microbial reduction of CO2.

Thermal decomposition of organic matter.

Both sources imply organic activity so possibly your question encloses that much-contested question about whether there was or not life on Mars in the past.
Regardless there were or there were no life, Lefèvre et al.(2009), clarify the occurrence and possible sources for methane on Mars from what we know with our current observation possibilities:

"The detection of methane on Mars has revived the possibility of past
or extinct life on this planet, despite the fact that an abiogenic
origin is thought to be equally plausible"

They continue...

"An intriguing aspect of the recent observations of methane on Mars is
that methane concentrations appear to be locally enhanced and change
with the seasons."

And finally:

"We find that photochemistry as currently understood does not produce
measurable variations in methane concentrations, even in the case of a
current, local and episodic methane release. In contrast, we find that
the condensation–sublimation cycle of Mars’ carbon dioxide atmosphere
can generate large-scale methane variations differing from those
observed."

This is still on debate and maybe someone can contribute quoting more recent articles, but the occurrence of Methane on Mars soil is measured, but this do not provide a proof that there was life on the planet.
That condensation-sublimation cycle may lead to CH4 storage on soil around the poles, and form a kind of "Methane permafrost", but formed for physical-chemical processes with no life interaction.
Also asking for "large amounts of Methane on soil", the answer possibly is no too, because either Mars had life, Earth's organic activity has developed big Methane Clathrate deposits on Oceanic Crust because of the listed organic associated process.
To recognize an organic origin of CH4, isotopes of C of the samples should show low concentrations of heavy C14, as life prefers to use lightweight ones: C13/C12
.
That hypothetical biologic Methane would be found on the big depression that was supposed to have a water ocean. The latest formed on soil would have been liberated to the atmosphere at the death of the ocean (because of pressure decrease), but rests of organic CH4 could maybe be found drilling the zone.
The new of past life occurrence has not yet been published, and could come from other chemical compounds.
I usually cross my fingers when I think about it.
Lefèvre, F. Forget, F. "Observed variations of methane on Mars unexplained by known atmospheric chemistry and physics."Nature (2009)


What method do I use to derive the organic material content (as a percentage) per layer in SoilGrids

All weight percentages are calculated using the same formula:
Mass Fraction/Total Sample Mass
There are two different values for organic material in a soil and they're derived by different techniques:
If you want to know how much bioavailable organic material is in the soil I was taught to use a chemical reagent to oxidise and strip organic carbon from the soil, saturated soil samples are weighed before and after the test to estimate the weight of organic matter so removed or a titration can be performed on the soil leachate to determine the exact amount of carbon oxidised.
If you want the total soil carbon weigh a dried sample then crush it and put it in a crucible over a Bunsen Burner until it stops smoking, the sample also darkens as it starts to burn and then turns pale once all the carbon has been burned out of it, and reweigh it the difference is all the soil carbon.


The standard stratigraphic nomenclature is a chronostratigraphic system based on palaeontological intervals of time defined by recognised fossil assemblages.

That's wikipedia for you. This is incorrect. The point of a Global Boundary Stratotype Section and Point (GSSP) is to identify a global boundary with a very specific archetypical example. While a recognizable and global fossil assemblage is preferred, sometimes there are better choices and sometimes such assemblages don't exist.

For example, the stratigraphic boundary that marks the start of the Cenozoic Era, (and the Paleogene System, Paleocene Series and Danian Stage) is a millimeter thick layer of fossil-free clay near El Kef, Tunisia. This clay layer was laid down about 66 million years ago and can be found in many places around the world. This layer is distinct, unique, and occurs worldwide. That clay layer contains the remnants of the dinosaur killer asteroid.

  How are stratigraphic limits defined before the Phanerozoic?

Getting to point of the question, the base of the Ediacaran "is defined as the base of the Marinoan cap carbonate (Nuccaleena Formation) in the Enorama Creek Section of the central Flinders Ranges, Adelaide Rift Complex, South Australia." The GSSP is the archetype, but as with that thin layer of red clay, this layer of cap carbonate can be found in many places around the world. That layer of cap carbonate represents when a worldwide glaciation event ended.

All of the International Commission on Stratigraphy boundaries that predate the base of the Ediacaran are currently defined in terms of time called Global Standard Stratigraphic Ages (GSSAs). That's a fancy name for a rather arbitrary point in time.


Is the effect of Earths position relative to sun large or small compared to CO2 level in climate change?

The changes Camilo Rada discusses repeat annually so they average out over longer timescales and have no effect on climate. The flares reach less than $1\%$ of the distance to earth and they are a recurring effect so they also average out.

Greenhouse gases have a cumulative effect.

Solar activity is included in the IPCC.


Soil is an interesting case because although it is non-renewable (at any useful rate) as a 'bulk material' once removed from the ground, the nutrient content of soil can be renewed with fertilizers.

What a soil-scientist would understand as 'soil' is ultimately produced from the physical and chemical breakdown of solid bedrock at the base of the soil horizon. The rate at which this happens for natural soil production can vary substantially depending on the climatic conditions and other factors, but typically could range from 0.1 to 2.0 mm/yr.

In many intensively farmed regions, (top)soil is being removed by erosion much faster than it is being replaced by natural process. Removal of vegetation cover is enough to expose bare soil to rainsplash erosion at rates much greater than it is renewed. Once soil is bare, it becomes much more susceptible to erosion.

I think the additives you are referring to replenish the nutrient content of the soil, and not the the bulk material that would be produced by bedrock decomposition. With careful management, the fertility of existing soil can be maintained. But if the soil is allowed to be washed off or erode, for all practical purposes, the rate of replenishment is not fast enough for it to be classed as renewable in that sense.

This site has links to more aspects surrounding this issue.


How does nature dilute Ocean and Seas so that we can swim in them?

You hit on the main reason why sea water is fairly clean, which is the fact that the sea is so vast. Salt water kills some micro-organisms, but by no means all. The sea is teeming with countless trillions of them, some dangerous but most not. The sea is full of hungry animals which feed on animal detritus. Some of these animals are small, like anemones and corals, and some are large, mostly species of fish and hagfish. Some dead vertebrates like whales sink down into the abyssal ocean depths, where they provide a feast for various deep sea creatures. This has been going on for many millions of years, and many a dinosaur has been eaten and dissolved away by creatures beneath the waves.

The many plants (sea grass and mangroves etc) and algae (seaweeds) also require nourishment, some of which comes from non-biological sources, and some from the excreta and decaying bodies of birds and other animals. Plastic is washed ashore and broken down into smaller and smaller fragments. Some beaches around the word are sufficiently polluted that they are classed as dangerous, and unfit to swim in, but may nevertheless seem to be clean. A few such beaches are in UK, so there must be some in America as well.


What is the name of the sea in this image?

That's the Caspian sea, considered the largest enclosed inland body of water on Earth by area. It is bounded by Kazakhstan to the northeast, Russia to the northwest, Azerbaijan to the west, Iran to the south, and Turkmenistan to the southeast.


What is the basis for the Geologic Time Scale

Here is an answer that matches the wording in this question.

Nice summary from http://hyperphysics.phy-astr.gsu.edu

Principles for Relative Dating of Geological Features
From over two hundred years of careful field explorations by geologists, a number of practical principles for determining the relative dates of geologic features have emerged. The assignment of numerical ages to these relative dates had to await the development of radiometric dating.

Law of Superposition**: For sedimentary rocks, each bed is older than the one above it and younger than the one below it.
Principle of Original Horizontality. Layers of sediment are generally deposited in a horizontal position. This is useful even if beds of sedimentary rock have been subsequently tilted.
Principle of cross-cutting relationships. A fault or intrusion is younger than the rocks affected by it.
Inclusions: the rock mass containing the inclusions is older than the rock providing the included material.
Unconformities: interruptions of sedimentation with removal of material by erosion and then a resumption of deposition can place rock strata in contact that have a gap of time and material between them.
Principle of fossil succession: fossil organisms succeed one another in a definite order. The fossils observed help to identify the time period in which the organism lived.

Does anyone know if there a published book that gives a comprehensive history of geologic time scale (looking for more than summary that is presented in countless text books)?


Why is the sky bluer in winter than in summer?

The angle of the sun and humidity, indeed have a major effect on the color of the sky. To start, when there is a higher humidity level there is obviously a greater quantity of water vapor in the atmosphere. This leads to more of what is called Mie scattering. Mie scattering in this scenario is when the water vapor and water droplets direct more blue spectrum of light back into space causing you to see a smaller portion then what is possible with less scattering. Depending on where you live the seasons vary for when there is the least amount of humidity.

Now secondly, if you live between 30-60 degrees North or South, the suns angle changes enough, that the spectrum of light is affected. When the sun is closer to the horizon, the light is traveling through more atmosphere than it would if the sun were directly above. This leads to Rayleigh scattering, which end and end directs more blue light to your eyes.


The main reason why the International Date Line doesn't run down the 180° meridian as you have suggested is because all nations determine their own standard time zones, applicable only on land and adjacent territorial waters of that country. This date line is not based on international law, but on national laws. The International Date Line is simply just an artificial-construct decided by cartographers.

This means that any country near the date line can shift their national time to either side of the International Date Line if they wish to. There have been several historical examples of this occurring, such as when the Republic of Kiribati gained independence and acquired new islands as a part of its territory across the International Date Line. Obviously no nation wants different parts of its territory running on different dates so the government of that country will choose unilaterally to change their nations time-zone how they see fit. This creates the zig-zagging International Date Line we have today.

Though, it is worth noting that in international waters time-zones do follow the 15° wide longitudinal lines as you have suggested as being ideal.

You may find this link useful:https://en.wikipedia.org/wiki/International_Date_Line


Ice being less dense than water, icebergs float to the degree they displace water, with about 1/8 of their mass above the surface. Icebergs are also dynamic, melting from exposure to sunlight, warm air and water, eroding, and fracturing, and pushed by both wind and waves. (Notably the descriptions used in the Wikipedia article generally apply to the shape of that small portion of an iceberg visible above the surface, not the gross geometry of the whole berg.)
Geophysicist Henry Pollack explored the potential stable positions of icebergs in a Physics Today article titled "Tip of the Iceberg":

When a totally submerged lower-density body is released, the buoyancy
force causes it to rise until it reaches a floating equilibrium. The
tip then rests above the surface and the root below it, with the mass
of each determined by the density contrast between the floating solid
and the surrounding fluid.

A floating object is only stable to the extent that its center of gravity is aligned above its center of buoyancy, Pollack writes, "...ice cylinders floating in water will stabilize in only two orientations—with the cylindrical axis either perpendicular or parallel to the water surface;" With an idealized ice-like cylinder 9/10 the density of water, the mass can't be stable if it's taller than it is wide.
The geometry won't be much different using an idealized cone shape -- a cylinder widening along its length -- for your mountain. It can only be short and squat,  and if it's at all unbalanced at any point in its life, it'll flip to a new stable equilibrium, on its side or upside-down.


Do current general circulation models model climate oscillations?

How the models do at this sort of interannual variability for the current climate is described in Section 9.5 of the Fifth Assessment Report (AR5). For example, the section about ENSO says,

  The representation of ENSO in climate models has steadily improved and
  now bears considerable similarity to observed ENSO properties.
  However, as was the case in the AR4, simulations of both background climate (time mean and seasonal cycle, see Section 9.4.2.5.1) and internal variability exhibit serious systematic errors, many of which can be traced to the representation of deep convection, trade wind strength and cloud feedbacks, with little improvement from CMIP3 to CMIP5.

  While a number of CMIP3 models do not exhibit an ENSO variability maximum at the observed 2- to 7- year time scale, most CMIP5 models do have a maximum near the observed range and fewer models have the tendency for biennial oscillations. In CMIP3 the amplitude of El Niño ranged from less than half to more than double the observed amplitude. By contrast, the CMIP5 models show less inter-model spread (Figure 9.36). The CMIP5 models still exhibit errors in ENSO amplitude, period, irregularity, skewness, spatial patterns or teleconnections.

  ...

  Detailed quantitative evaluation of ENSO performance is hampered by the short observational record of key processes and the complexity and diversity of the processes involved. While shortcomings remain, the CMIP5 model ensemble shows some improvement compared to CMIP3, but there has been no major breakthrough and the multi-model improvement is mostly due to a reduced number of poor-performing models.

In short, it's a bit of a mixed bag and it will depend on which metrics you use to assess the variability.  Something like the NINO3.4 index is simple to calculate, but getting a good (or bad) score doesn't necessarily indicate how well your model simulates the relevant processes (e.g., ocean mixed layer dynamics, air-sea interactions, convection).

Section 9.5 also has information on other modes of variability, including the Pacific Decadal Oscillation, the Madden-Julian Oscillation, Atlantic Meridional Overturning Circulation, etc.  It's worth a read.


Is there any significance of lacustrine gastropoda fossils regarding paleoenviroment interpretation?

Shell stable isotopes, for oxygen and carbon reveals, if the gastropoda had lived in brackish, lacustrine or palustrine environment.

For discussion please see paper below.

Latal, C., Piller, W. E., & Harzhauser, M. (2004). Palaeoenvironmental reconstructions by stable isotopes of Middle Miocene gastropods of the Central Paratethys. Palaeogeography, Palaeoclimatology, Palaeoecology, 211(1-2), 157-169.


The way I understand it, the net longwave radiation $L^\star:=L^\downarrow-L^\uparrow$ (maybe with different sign), i.e. the difference between downwelling and upwelling radiation, can be viewed as a vector field (with vanishing horizontal components under the assumption of homogeneous horizontal radiation distribution). This vector field has a divergence $\nabla\cdot L^\star=\frac{\partial L^\star}{\partial z}$.

This term occurs in equation (1) of the paper you referenced as part of the heating rate. Since non-vanishing divergence is in a vector field is associated with the field having a source or sink, this corresponds to heating/cooling of the atmosphere.


Can thunderstorms be thought of as a heat engine?

Yes, they can.

Broadly speaking, most dynamical atmospheric phenomena are heat engines in one form or another. Ultimately the heat source is due to sunlight heating up the ground, and the cold sink is the upper atmosphere, which stays cold due to emitting thermal radiation into space. Large convection cells (such as tropical cyclones or the Hadley cells) act broadly like Carnot engines, adiabatically expanding packets of air as they're brought upwards from the ground to the upper atmosphere, then isothermally compressing them as they radiate into space, then adiabatically compressing them as they travel back down to the surface, and then isothermally expanding them as they pick up heat from the ground. (This description is a very rough approximation to the reality.) The net effect is to transfer heat from the ground to the upper atmosphere, while converting a small amount of that heat into kinetic energy, which keeps the whole thing moving.

Thunderstorms are quite an interesting case, because they are driven by latent heat as well as sensible heat. The air near the surface is not just warm but moist, due to evaporation and evapotranspiration from plants. As air rises it cools. Cool air can hold less moisture than warm air, so this can lead to condensation (i.e. the formation of clouds and rain). This condensation releases heat. A thunderstorm happens when condensation releases so much heat that the air starts to rise even faster, pulling more air up behind it. The moisture in this air then condenses, releasing more heat and pulling more air up, and so on. This is why thunderstorms often rise to a much greater height than the surrounding clouds.

Condensation releases heat, but evaporation uses up heat, which is why you feel cooler when you sweat. When water evaporates it takes heat away from the surface. That heat was put there by sunlight, and it gets released back again at the top of the thunderstorm. So a thunderstorm is part of a large-scale heat transport process that begins with evaporative cooling at the Earth's surface, and ends with the heat from condensation being transported into the upper atmosphere and ultimately radiated away into space.


What part of a hurricane determines if it makes landfall?

Hurricanes make "landfall" when the center of the eye moves over land.

From the NOAA National Hurricane Center glossary:

  Landfall:
  The intersection of the surface center of a tropical cyclone with a coastline.Because the strongest winds in a tropical cyclone are not located precisely at the center, it is possible for a cyclone's strongest winds to be experienced over land even if landfall does not occur. Similarly, it is possible for a tropical cyclone to make landfall and have its strongest winds remain over the water.

Below is an example image showing when landfall occurred for Hurricane Harvey:


An Inverted or Perched water table is a water table that is above the main or regional water table in an  unconfined aquifer.  The perched water table is generally above a layer of low permeability material such as clay.  In the image below, notice that there is an "inverted" water table along bottom of the perched water table.


Why doesn't the 71% water of the earth dry or evaporate?

There are two ways this problem needs to be looked at.   The first is more astronomy than Earth science.  The Earth as an entire system is largely contained.   Its gravity and magnetic field retains nearly all of its elements.   Earth does lose hydrogen and helium and cosmic rays will split water molecules leading to a loss of an impressive amount of hydrogen and as an indirect result a loss of water, but this is loss irrelevant compared to the size of the oceans.    More detail here.  Space dust, comets and asteroids contain water so some water is returned from space too.

By the upper estimate in one article, 50,000 tons of hydrogen per year works out to about 450,000 tons of water lost every year. (and 400,000 tons of oxygen added as a result).    Compared to the mass of Earth's oceans those numbers are small.  450,000 tons per year, or 450 trillion tons over a billion years is nothing compared to the 1.3 million trillion tons of water Earth has in its oceans.   By the highest estimate, it will take 30 billion years at the current rate and at the Sun's current luminosity for Earth to lose just 1% of its oceans.  (Will look to update with other estimates).

As for the rest of the question, once we recognize that loss into space is insignificant, then virtually all water is continuously cycled though the water cycle or hydrological cycle.   Very little water gets destroyed or chemically transformed.   Nearly all of it, even of millions or billions of years, evaporates, or, turns into ice, or gets absorbed by plants, or seeps underground, but it always returns.   Evaporated water returns to Earth as rain.   Water that gets frozen on the ice caps eventually melts back into the oceans.   Water absorbed by plants or that seeps underground does eventually get returned to the surface by plate tectonics or volcanism.   Plants that store water return it when the plant is eaten.  Water is very hard to destroy, so it stays remarkably constant on Earth over time.


Do you have any informations about fossil-rich cherts from Scandinavia?

What you are looking for is information about the "Oslofeltet" (Oslo-field) in Norway (dated to be from the Ordovicium period, 443 - 488 million years old). This is a concentrated field of of fossils. There is a Sement museum ('cement') in a small place called Slemmestad where it is possible to view fossils from what was formerly an ocean bed. Geologicaly speaking, the entire area around Slemmestad is very interesting.


hydrogen is the most common element in the universe, Oxygen is the third most common element in the universe, hydrogen + oxygen + heat/energy = water. Water is literally the most common compound in the universe.


The Andaman and Nicobar Islands are neither orogenic or volcanic in origin. They are in fact an accretionary wedge, i.e. an accretion of sediments and oceanic crust "scraped" from the subducting Indian plate. See for instance the description in the first chapter of the aptly titled The Andaman–Nicobar Accretionary Ridge:

  The islands are an exposed segment of the accretionary wedge (outer arc) of the Sunda subduction system, where the Indian Plate subducts beneath the Sunda Plate. Ongoing uplift of the sediment-dominated accretionary wedge has exposed, over a relatively small area, a diverse range of rock types associated with the subduction complex (dismembered ophiolites, volcanic-arc rocks, trench-slope deposits, submarine fan turbidites, pelagic sediments and the sediments of shelf and reef environments), making it an ideal area for investigating subduction processes.

(Unfortunately, other chapters with more detailed descriptions are not open access.)

Note that if some of the sediments are indeed volcanic in origin, it does not mean that volcanism is responsible for building the archipelago, like it was for the Chagos-Laccadives ridge for instance, to stay around India. It is the accretion of sediments in the subduction trench, and their subsequent uplift above the sea, that created the islands.


Colder winters along the North American Atlantic northeast

As air moves over the surface of the earth, the properties of the surface (such as temperature) can alter the air. Since at those particular latitudes, the predominant wind direction is from the west and partially the north, it is important to note what is north and west of both locations.

West of the northeast Atlantic is land, and northwest is Canada. This means that the air is drier, and prone to have characteristics of mimicking continental- polar (cP) air. Continental polar air tends to be dry (since it is over land) and cold (since it is coming from an area that receives less sunlight).

West of the northwest pacific is the Pacific Ocean, and northwest is still the Pacific Ocean. This means that the air is more moist and prone to have characteristics mimicking the air over the ocean, called Maritime polar (mP). Since the water tends to warm slower than the land and also slower than the land, the air over the water is usually warmer during the winter and cooler over the summer than the air over the land.

To summarize:

At those latitudes, the wind usually blows from the north and west.
During the winter, air over the ocean is warmer than air over land.
North and West of the Northwest coast is the Pacific ocean, while land is west of the Atlantic coast.
Therefore, the winter in the northwest coast is usually warmer than the winter along the northeast coast.


Karst topography on land is characterized by sinkholes, springs, losing streams, and caves.  They are formed by the dissolution of easily dissolved carbonate rock such as limestone and dolomite.  The rock is dissolved by carbonic acid in rain.

From Wikipedia:

  The carbonic acid that causes karstic features is formed as rain
  passes through the atmosphere picking up carbon dioxide (CO2), which
  dissolves in the water. Once the rain reaches the ground, it may pass
  through soil that can provide much more CO2 to form a weak carbonic
  acid solution, which dissolves calcium carbonate.

Here is an illustration of karst topography:

Source:  //www.wandelgek.nl/?p=18828&lang=en

Here is an illustration of karst formation:

Source:  http://slideplayer.com/slide/3400196/


What are the key differences between warm and cold core cyclones?

Key differences are in structure, location, environments they thrive in.  To compare/contrast these storms I'll use a mid-latitude cyclone for the cold core cyclone and a hurricane for the warm core cyclone.

Structure
The hurricane is nearly symmetric and devoid of fronts.  The mid-latitude cyclone is asymmetric (comma shaped with a long tail) and has fronts associated with it.

Location and Movement
Hurricanes form in the tropics (but not around the Equator) and initially move from east to west with a discrete well-defined low pressure center.  Hurricanes move with the wind.  Mid-latitude cyclones occur in the mid-latitudes and move west to east with centers of low pressure that may dissipate and re-form further downstream.  Mid-latitude storms move as temperature advection drives pressure falls ahead of the storm.

Environment
Hurricanes need warm ocean surface and weak vertical wind shear throughout the troposphere to develop.  Mid-latitude storms are at home with shear and require horizontal temperature gradients to develop.

Hurricanes can transition into cold-core cyclones once they exit the tropics.  It is possible, but not common, for a mid-latitude cyclone to transition into a warm-core tropical cyclone.


Is there an earth science discipline, or subdiscipline, that only studies magma or lava?

Perhaps they are called Igneous Petrologists ?

Someone who studies magma/lava flows tends to go by Geophysicist because they inherently study continuum mechanics and fluid flow.


Siberia (Beringia) during last glacier period

This paper basically summarizes the thinking behind the highly-productive mammoth step theory:

Zimov, S.A., Zimov, N.S., Tikhonov, A.N., Chapin, F.S., 2012. Mammoth steppe: a high-productivity phenomenon. Quaternary Science Reviews 57, 26–45. https://doi.org/10.1016/j.quascirev.2012.10.005

The idea is basically that a large herbivore density (comparable to modern day intact African Savannah ecosystems) kept soil moisture low and reduced permafrost temperatures. This was favoring gramminoids (grass like plants) that are much more productive than the present day prevailing mosses. Plant productivity in these regions is usually limited by nitrogen (other ecosystems are carbon limited). The higher than today herbivore population provided a lot of nitrogen input from dung and urine propelled the productivity of plants, which in turn allowed for more herbivores. Low temperatures and shorter summers also limited damage to gramminoids, thus they could grow faster in the next season. The ecosystem had several positive feedback mechanisms sustaining high productivity.

When humans arrived in the region, they hunted all the herbivores. The system collapsed and lost its productivity.


The boom* is a cleanup prototype. From the OceanCleanup website:

  The Ocean Cleanup deployed a 100 meter-long barrier segment in the North Sea, 23 km off the coast of The Netherlands on the 22nd of June 2016.

  OBJECTIVE AND SET-UP

  To investigate the durability of our design, we deployed a system segment in the North Sea. At this test site, conditions are more severe than those in the Pacific Ocean, due to the North Sea's strong tidal currents, and the test site's short, steep wave patterns.

  The objective of the North Sea prototype was twofold;

  Test the boom design on a small-scale for survivability in extreme conditions
  Gaining experience as an organization in the ocean deployment of a cleanup array

  FINDINGS

  During an inspection of the North Sea prototype in August, we noticed the two outermost air chambers were bent out of shape. Thanks to underwater footage we were quickly able pinpoint the cause; shackles had disconnected from the mooring, which increased the forces on the ones remaining as well as the floater. After our diagnosis, we continued to closely observe the situation and decided to take the barrier back to shore after close to two months.

The design has changed since (bottom of page).

These Youtube fragments have some more shots:

Video 1
Video 2 (Dutch)
Video 3

That last video goes into detail about it's design and later versions. The comments state that

  the new North Sea tests are aimed at assessing two variations of floater-screen connections as well as the application of antifouling on the screen

* A long pole, often heavy, e.g. along the foot of a sail. In this case, sheets/screens are hanging down from it.


Movements of the tectonic plates - collison between Indian Plate & Eurasian Plate

As the continental crust is too buoyant (light) to be subducted, when two continents collide they smash against each other creating a mountain range, in this case the Himalayas.
This process happen trough thrusting and folding of the plates, leading to something called lithospheric shortening. Which basically means that the plates (lithosphere is the stuff of which plates are made of) gets shorter. In other words: the area of the colliding continents gets smaller. And the missing area is used to build up the mountains by thrusting and folding, a process that is nicely illustrated by the following animated GIF that I put together from a video by the Department of Earth Sciences of UC Santa Barbara.

In this question, this process is also discussed.

In regard  of the Monsoon, it is not a direct consequence of this collision. But it is due to the fact that Eurasia is a big continent close to the equatorial Indian ocean. Now, as this collision helped to put together Eurasia and bring it closer to the equatorial Indian ocean in the area associated with the Monsoon, you can argue that played a significant role in creating the Monsoons as we know them.


At what point are water droplets too small to make a rainbow?

Some time ago I posted this answer about how rainbows are formed, and the Wikipedia link Trond Hansen posted mentions droplet size relative to the wavelength of light.

For a rainbow to form, the droplet size has to be large enough, relative to the color with the longest wavelength of visible light, for it to be refracted before reflecting off the backside of the droplet. Refraction occurs because, as the wavefront encounters the change in density between air and water, it slows down. This implies that a droplet would have to be greater than half the wavelength of red light, which is about 740 nm, or about 370 nm.1 Also, the light responsible for producing the rainbow enters the droplet off-center and reflects off of the backside of the droplet off-center, so the droplet's diameter would need to be a bit larger than 740 nm.

https://en.wikipedia.org/wiki/Light


What is the source of lava of volcano? From magma below crust? Or from molten crust by rubbing?

Both are correct to some degree.

Basalts are usually the result of direct mantle melting, below the crust. This is the case in the famous volcanos of Hawaii and this is also the case in the most common type of volcanism on Earth: the mid-ocean ridges (albeit hidden below several kilometres of sea water).

Most other eruptive rocks (rhyolite, andesite, etc) are usually the result of either melting of the crust, or interaction of mantle melts (basalts) with crustal rocks. A very large portion of these rocks erupt above subduction zones (most obvious example being the Ring of Fire). The reason is that wet subducting oceanic lithospheres get heated and lose their water. We usually think of water as something that puts out fires, but in the deep Earth it actually lowers the melting point of rocks. This causes melting in the crust, and eventually erupts as volcanoes.

This is a very simplified overview of the subject, and it's a very active area of scientific research with sometimes opposing opinions. But the basic story is somewhat established: some volcanoes (mostly basalts) are products of mantle melting, while others (mostly other stuff) are products of crustal melting.


Does "Arctic Greening" mean an increase in the spatial extent of vegetation, an increase in particular types of vegetation, or both?

You have an unclear question. See my comment on the question itself.

Answering just the question:

I've not seen a formal  definition of arctic greening.  Conceptually it's replacing a landscape that is in effect a cold desert with one that has:

Longer growing season.
Greater biodiversity
Greater gross photosynthesis.

You would think that it would also be greater net photosynthesis too, but much of the arctic has large deposits of peat moss, forest duff and sedges. With warmer temperatures we will likely see greater bacterial action on the peat. Not clear which way the carbon/acre figure will move.

It's also not clear what the effect of an open oceans in the high arctic will be.  Depending on the nutrient levels in those waters could see a lot more phytoplankton. BVOC exchange between ocean and atmosphere?

You can get a first level approximation substituting latitude for time. I expect BVOCs to disperse fairly quickly so you would need to measure at ground level. Analyzing a bunch of sites that are representative of the various major communities -- Boreal forest, tree line, tundra/puckey-brush (scrub willow, birch) Tundra/moss, forbs; Rock.

For a preliminary analysis you don't even need to go to the arctic. Use a convenient mountain.

That can nail down quantities of BVOCs. Correlate that with HCOH to see how good a proxy HCOH is for BVOC.

This leaves a bunch of unanswered questions:

Is the time frame for the degradation of HCOH similar to for other BVOCs?  You may have to do radioactive tracer tests in containers set at similar conditions of temperature, pressure and UV illumination.

What are the degradation products?  What are the effects of these?  Do any of the original products or their degradation products acts as catalysts?

I think you have bitten off a big research project.