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20 Cards in this Set

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uniformitarianism
A principle that geologic processes that occurred in the past can be explained by current geologic processes.
catastrophism
A principle that states that geologic change occurs suddenly.
paleontology
The science that deals with the study of past life (fossils).
paleontologists
Scientists who study past life using fossil data.
relative dating
Any method of determining whether an event or object is older or younger than other events or objects.
sedimentary rock
A rock that forms from compressed or cemented layers of sediment.
superposition
A principle that states that younger rocks lie above older rocks if the layers have not been disturbed.
unconformity
A break in the geologic record created when rock layers are eroded or when sediment is not deposited for a long period of time.
law of crosscutting relationships
The principle that a fault or body of rock is younger than any other body of rock that it cuts through.
absolute dating
Any method of measuring the age of an event or object in years.
radioactive decay
The process in which a radioactive isotope tends to break down into a stable isotope of the same element or another element.
radiometric dating
A method of determining the age of an object by estimating the relative percentages of a radioactive (parent) isotope and a stable (daughter) isotope.
half-life
The time required for half of a sample of a radioactive isotope to break down by radioactive decay to form a daughter isotope.
intrusion
A mass of igneous rock that forms when magma is injected into rock and then cools and solidifies.
What are isotopes of an element?
Isotopes of an element have nuclei with the same number of protons (the same atomic number) but different numbers of neutrons. Therefore, isotopes have different mass numbers, which give the total number of nucleons-the number of protons plus neutrons
Where are most fossils preserved?
Most fossils are preserved in sedimentary rock.
Where do you find the oldest fossils?
In the oldest layers of rock.
What happens after every half-life?
Half of the parent material will have decayed and become daughter material.
Why is the fossil record not complete?
The fossil record is incomplete because we don't have a record of every organism that ever lived; animals with soft parts don't fossilize; weathering destroys fossils.
How do you figure out the absolute age of rock?
If you know the half-life of a sample, and can measure the ratio of parent and daughter isotopes, you can find the absolute age of the rock.