Rock Layers / Geologic Time Overview (23/24)

Rock layers can tell us the history of Earth: how the Earth has changed, how long it's existed, as well as what animals used to live here and what happened to them.  

• True 

• False

What type of rock forms in horizontal layers over time (shown in the picture)? 

• igneous

• sedimentary

• metamorphic

Sedimentary rock is formed by...

• sediment getting broken down, deposited by wind or water and then compacted and cemented together over long periods of time

• heat and pressure from Earth's interior 

• from hardened magma and lava

Where is the OLDEST rock layers located? (known as the Law of Superposition)

• the highest layers at the top

• the lowest layers at the bottom

• the layers in the middle

When geologists compare existing rock layers to each other in order to determine which layer is older or younger than the other, they are using a process called  ______________.

• relative dating

• absolute dating

True or False: Earthquakes can cause rock layers to become misaligned. 

• true

• false

Trilobites serve as good index fossils because

• they only lived for a short/certain period of time but were also very common at that time (found all over the world)

• they can be carbon dated to 1 billion years ago

• existed for a very long period of time & show up in multiple rock layers 

When erosion results in missing rock layers / gaps in the geologic record, we call that an _______. 

• unconformity 

• intrusion 

• extrusion

Magma that cuts through already-existing rock layers is called an ____________.

• intrusion

• extrusion

• unconformity 

What is absolute dating of a rock or rock layer?

• When scientists study a rock in great detail and analyze its chemistry to determine its exact age

• When scientists use other rock layers to determine the relative ages of rocks compared to other layers in the are