Radience

Fossils and Earth's Past

Science

absolute dating

any method of measuring the age of an object, like tree rings or carbon dating
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carbon film

a thin layer of carbon preserved as a fossil
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cast

a fossil formed when dissolved minerals fill a mold and harden
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eon

the largest unit of the geologic time scale, it is divided into eras, periods, and epochs
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epoch

a unit of geologic time longer than an age but shorter than a period
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era

the second-longest unit of geologic time, it is divided into periods
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evolution

the change in a species over time
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extinction

the death of all members of a species
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fossil

the preserved traces and remains of an organism that lived long ago
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geologic time scale

a timeline of Earth's history based on major changes
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half-life

the time it takes for half the atoms of a radioactive isotope to decay
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index fossil

a fossil from an organism that existed for a short time, it is used to determine the age of other fossils
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isotope

an atom of the same element with a different number of neutrons
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law of superposition

the oldest rock layers are at the bottom and youngest are at the top
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mold

a rock fossil created when a buried organism dissolves
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period

a unit of geologic time that lasts tens of millions of years, it is longer than an epoch but shorter than an era
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radioactive decay

the breakdown of an unstable atomic nucleus, this releases particles and energy
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radiometric dating

comparing the amount of radioactive and nonradioactive isotopes to determine rock age
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relative dating

a method of comparing fossils or rocks to determine which is older
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trace fossil

a fossil formed in soft sedimentary rock, like a footprint
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unconformity

a gap in a rock layer caused by erosion or periods without sediment deposition
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uniformitarianism

the theory that geologic processes are the same today as they were in the past
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