Index fossils
Old organisms
Mold fosdils
Young organisms
Rocky fossils
Index Fossils
Cast fossils
What kind of fossils are used to date rock layers?
They are collectable items
To observe lifestyle changes of humans
To create chemical energy
Index fossils are commonly used to match rock layers; if two rock layers have the same index fossils, then they're probably about the same age
The fossils that are very distinct at certain times of Earths history and they date rock layers
They help to determineage of rock layers
None of these above
How are index fossils used?
Index fossils
Artifacts in the rock
Chemical abalysis of rock substances
Rock sediment
Fossils and knowing what organisms looked like at certain times
Stalagmites in caves
Marker fossils
Color
Knowing what organisms looked like at certain times also helps date rock layers
What helps to date rock layers?
They leave behind sediment
Fossils become less rare  from layer to layer
The fossils that are very distinct at certain times of Earths history are called index fossils
They match the mineral deposits
As organisms change over time, they look different, so older fossils will look different than younger fossils
Rock layers of the same age have the same index fossils
They match the water levels
How are fossils used to match up rock layers?
The fossils that are very distinct at certain times of Earths history
These fossils are very distinct at certain times of Earths history and are commonly used to match rock layers
They show extinction force
They show hieroglyphs
They help to split rocks to layers
They show water levels
Rock layers of the same age have the same index fossils
What key do index fossils play in dating rock layers?
Some animals only existed during certain time periods before becoming extinct. It helps to date that layer of rock where these animal fossils are present
Rock layers change color
It shows how many of a species lived
It shows young fossils
Organisms helped shape rocks and layers upon their extinction
Some organisms only survived for a short time before going extinct
It shows glaciers
How can extinction help to date rock layers?
They show us flora of the past
Knowing what organisms looked like at certain times also helps date rock layers, and index fossils are the fossils that are very distinct at certain times of Earth's history
The fossils that are very distinct at certain times of Earths history and help date fossils
For fuel
They help to determineage of rock layers
They are used to mark water levels
They are used to identify extinct animals
As markers for glacier activity
How are index fossils useful?
Fossils can be used to match up rock layers. As organisms change over time, they look different. Older fossils will look different than younger fossils. Some organisms only survived for a short time before going extinct. Knowing what organisms looked like at certain times also helps date rock layers. Some fossils are better than others for this use. The fossils that are very distinct at certain times of Earths history are called index fossils. Index fossils are commonly used to match rock layers. You can see how this works in Figure 2.30. If two rock layers have the same index fossils, then they're probably about the same age. 