a new 'superviscous' layer in earth’s lower mantle has been discovered the breakthrough could explain why parts of earth’s sinking tectonic plates sometimes stall and thicken 930 miles (1,500km) underground it could also explain why earthquakes occur deep inside the earth’s interior, suggesting it is hotter than previously thought shown here is a simplified image of a slab from one of earth's tectonic plates sinking through the upper mantle above,  then stalling and pooling at a depth of 930 miles, where university of utah experiments suggest the existence of an extremely stiff or viscous layer in earth  the research was carried out by scientists at the university of utah by crushing minerals between diamonds to replicate conditions in earth's interior earth's main layers are the thin crust four to 50 miles (six to 80km) deep, a mantle extending 1,800 miles (2,900km) deep and the iron core but there are subdivisions the crust and some of the upper mantle form tectonic or lithospheric plates 60 to 90 miles (97 to 145km) thick that are like the top side of conveyor belts carrying continents and seafloors they are responsible for the formation of continents, and are still active   as earthquakes and volcanic eruptions show however, researchers have never been able to work out why the earth developed tectonic plates, but other planets did not last year, yale said it had solved the mystery   and said the key is tiny minerals within rocks the research suggests how and when earth came to develop one of its most distinct features   rigid tectonic plates   and why venus, earth’s twin like neighbor, never has 'we think it all comes down to the behavior of tiny grains of minerals within rocks,' said yale geophysicist dr david bercovici, lead author of research published  in the journal nature the researchers argue that in earth’s early days, mantle convection caused weak zones in the lithosphere   the outermost shell of the planet these zones persisted, developed into plate boundaries, and ultimately connected to form a global network of tectonic plates the weak zones, they argue, resulted from the tendency of mineral grains in rocks to shrink as the rock deforms this new layer is a ‘superviscous’ region, where liquids are under such intense pressure that they are extremely stiff it extends from 410 miles (660km) underground to 930 miles (1,500km) in laboratory experiments, the researchers found that an abundant mineral in the mantle called ferropericlase began to increase in strength at pressures equivalent to those 410 miles (660km) underground   the upper lower mantle boundary and this strength increased threefold at depths of 930 miles (1,500km) deep by simulating how it behaves with another dominant mineral at the same level   bridgmanite   the researchers calculated that the viscosity or stiffness of the mantle rock at 930 miles deep is 300 times great than at 410 miles deep to put that in perspective, on the pascal second scale the viscosity of water is 0001, peanut butter is 200 and this stiff mantle layer is 1,000 billion billion ‘the result was exciting,' said dr lowell miyagi, an assistant professor of geology and geophysics at the university of utah ‘this viscosity increase is likely to cause subducting slabs [ones that move under each other] to get stuck   at least temporarily   at about 930 miles underground ‘in fact, previous seismic images show that many slabs appear to “pool” around 930 miles, including under indonesia and south america's pacific coast ‘this observation has puzzled seismologists for quite some time, but in the last year, there is new consensus from seismologists that most slabs pool’ earth's main layers (illustrated) are the thin crust four to 50 miles (six to 80km) deep, a mantle extending 1,800 miles (2,900km) deep and the iron core but there are subdivisions the crust and some of the upper mantle form 60  to 90 mile thick tectonic or lithospheric plates that are like the top side of conveyor belts  university of utah geophysicist dr lowell miyagi holds a press that houses a diamond anvil, in which minerals can be squeezed a pressures akin to those deep within earth miyagi and a colleague in germany squeezed mineral crystals in a diamond anvil under pressures like those deep underground  dr miyagi added that the stalling and buckling of sinking slabs due to this stiff layer in the mantle may explain some deep earthquakes higher up in the mantle; most quakes are much shallower and in the crust ‘anything that would cause resistance to a slab could potentially cause it to buckle or break higher in the slab, causing a deep earthquake,’ he said dr miyagi also said the stiff upper part of the lower mantle may explain different magmas seen at two different kinds of seafloor volcanoes recycled crust and mantle from old slabs eventually emerges as new seafloor during eruptions of volcanic vents along mid ocean ridges   the rising end of the conveyor belt the magma in this new plate material has the chemical signature of more recent, shallower, well mixed magma that had been subducted and erupted through the conveyor belt several times but in island volcanoes like hawaii, created by a deep hotspot of partly molten rock, the magma is older, from deeper sources and less well mixed dr miyagi said the viscous layer in the lower mantle may be what separates the sources of the two different magmas that supply the two different kinds of volcanoes another implication of the stiff layer is that 'if you decrease the ability of the rock in the mantle to mix, it's also harder for heat to get out of earth, which could mean earth's interior is hotter than we think,' he said the findings could also indicate that earth's interior is hotter than thought, averaging 2,150°c (3,900°f) at the lower mantle boundary rather than 1,540°c (2,800°f) as previously predicted  scientists believe the average temperature and pressure 410 miles (660km) deep at the upper lower mantle boundary is 1,540°c (2,800°f) and 235,000 times the atmospheric pressure on earth's surface dr miyagi said that at the newly discovered viscous layer's stiffest area, 930 miles (1,500km) deep, the temperature averages 2,150°c (3,900°f) and the pressure is 640,000 times the air pressure at earth's surface such conditions prevent geophysicists from visiting earth's mantle, so 'we know a lot more about the surface of mars than we do earth's interior,' according to dr miyagi 'we can't get down there, so we have to do experiments to see how these minerals behave under a wide range of conditions, and use that to simulate the behavior of the earth' the finding was a surprise because researchers previously believed that viscosity varied only a little bit at temperatures and pressures in the planet's interior the study's simulations also determined that just below the 930 mile deep zone of highest viscosity, slabs sink more easily again as the lower mantle becomes less stiff ‘the earth has many layers, like an onion,’ said dr miyagi ‘most layers are defined by the minerals that are present ‘essentially, we have discovered a new layer in the earth this layer isn't defined by the minerals present, but by the strength of these minerals’
the university of utah earth 930 miles
research was carried out by scientists at the university of utah  they crushed minerals between diamonds to mimic earth's core  and they found there must be a new region 930 miles underground  the superviscous region could explain why some plates don't sink  and the findings also indicate earth's interior is hotter than thought 