These type of fossils are useful because they help tell us the relative age of rocks.
What are index fossils?
100
The time it takes for half of the radioactive atoms to decay into stable atoms.
What is the half-life?
100
On the Geologic Time Scale, eras are divided into ...
What are periods?
100
The process by which all the different kinds of living things have changed over long periods of time.
What is evolution?
200
Most fossils form when organisms die and are buried in...
What is sediment?
200
Magma that forces its way into rocks and hardens.
What is an intrusion?
200
This process is used to determine the absolute age of rocks.
What is radioactive dating?
200
Animals WITHOUT a backbone.
What is an invertebrate?
200
This era is often called the Age of the Reptiles.
What is the Mesozoic Era?
300
With this type of fossil, minerals replace all or part of an organism.
What is a petrified fossil?
300
Which layer is the youngest (relative to the other 3)?
Layer A
Layer B
Layer C
Layer E
What is layer A?
300
Scientists use this isotope to date materials that lived up to about 50,000 years ago.
What is carbon-14?
300
The earliest forms of life appeared during this part of the Geologic Time Scale.
What is Precambrian Time?
300
Fossils are almost always found in this type of rock.
What is sedimentary rock?
400
Describe how a cast is related to a mold.
A mold is a hollow area in rock in the shape of an organism.
If water gets into the mold it will deposit its minerals and sediments there, resulting in a cast.
400
What is the law of superposition, and how is it used?
The law that states that older rocks are located below newer rocks. It is used when determining the relative age of rocks.
400
This type of rock we can radioactively date.
What is igneous rock?
400
Precambrian Time - Paleozoic Era - Mesozoic Era - Cenozoic Era
What is this called, and why do geologists use it?
The Geologic Time Scale. Geologists use it because the time span of Earth's past is so great.
400
What are index fossils and how are they used? Use an example.
Organisms that were widely distributed but lived for only a short period of time. Used to determine the relative ages of rock layers. Example - trilobites
500
Name the three types of preserved remains.
What is tar, amber, and ice?
500
Describe unconformity.
A gap in the geologic record. A layer(s) of rock erodes away and a new layer forms directly on top. Where new rock meets very old rock.
500
What is a covalent bond?
When atoms share an electron.
500
What does the fossil record show about how life has changed on Earth?
Different organisms have existed and different groups of organisms have evolved over time.
500
Why do movements along faults make it hard for geologists to determine the relative ages of rock layers?
Faults cause rock layers to no longer line up because of movement along the fault. Remember faults are always younger than the rocks they cut through.