Rock Processes
What is weathering?
When rocks are broken down into smaller pieces
What are rock layers also called?
Strata
What does the law of superposition say about the oldest rocks in undisturbed layers?
They are at the bottom
How do fossils help scientists understand Earth’s past?
They show what organisms lived during different times and how life and environments changed
How old is Earth, according to the geologic time scale?
4.6 billion years
What is erosion?
When small pieces of rock are moved by wind and/or water
How long does it take for rock layers to form?
Millions of years
Where are the youngest rocks in undisturbed layers?
At the top
What do fossils show about organisms over time?
How they changed over Earth’s history
What is relative dating?
Using the order of layers to decide which rocks are older or younger
What is deposition?
When sediment stops moving and collects in a new area
What is often found in rock layers that gives clues about past life?
Fossils
What does the law of superposition help scientists determine?
The relative age of rocks and fossils
What kind of fossils help identify the age of rock layers?
Index fossils
What is absolute dating?
Using radioactive decay to determine the actual age
What is an intrusion?
When molten rock moves through cracks in rock layers and sometimes breaks the surface
What does each rock layer represent?
A time period in Earth’s history
In what type of rock layers does the law of superposition apply?
Undisturbed rock layers
Give an example of an index fossil from the slides.
Trilobites
Why is the geologic time scale important?
It organizes Earth’s history into sections
Why are intrusions useful to geologists?
They help determine the relative age of rock layers by cutting across them
What do fossils in rock layers provide evidence of?
Organisms and environments of Earth’s past
What is the key idea of the law of superposition?
Rock layers form in order, with the oldest at the bottom and the youngest at the top
What evidence do fossils provide in rock layers?
Evidence of Earth’s past life
What does the geologic time scale use to divide Earth’s history?
Rock layers, fossils, and major events like mass extinctions