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Geology and Fossils

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Mold
A cavity in rock where a plant or animal was buried.
cast
An object created when sediment fills a mold and becomes rock.
Eon
The largest division of geologic time.
Era
The second largest division of geologic time that includes two or more periods.
period
The third largest division of geologic time.
Epoch
Subdivisions of periods.
Extinction
The death of every member of a species.
Paleontology
The scientific study of fossils.
Paleontologist
A person who studies fossils.
Geologic time scale
A scale that divides Earth`s 4.6 billion-year history into distinct intervals of time.
Relative dating
Any method of determining whether an event or object is older or younger than other events or objects.
Superposition
A principle that states that younger rocks lie above older rocks if the layers have not been disturbed.
Geologic Column
an arrangement of rock layers in which the oldest rocks are at the bottom
Absolute dating
the process of establishing the age of an object by determining the number of years it has existed
Unconformity
a surface that represents a missing part of the geologic column
Fossil
the remains or physical evidence of an organism preserved by geologic processes
Trace fossil
any naturally preserved evidence of animal activity (footprints/tracks or animal droppings)
Index fossil
fossils or organisms that lived during a relatively short, well-defined geologic time span