14 terms

Chapter 8 Vocabulary - Geologic Timescale

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Catastrophism
the concept that earth was shaped by catastrophic events of a short-term nature
cross-cutting relationships
if one layer cuts through another, the one being cut through is older, states that the geologic feature which cuts another is the younger of the two features
Fossil
The remains or traces of an organism preserved from the geologic past
fossil succession
the principle that states that fossil organisms succeed one another in a definite and determinable order. Therefore, any time period can be recognized by it's fossil contents.
Half-life
the time required for one half of the atoms of a radioisotope to emit radiation an decay products
Index fossil
a fossil that is associated with a particular span of geologic time
Numerical date
data that specifies the actual number of years that have passed since an event occurred
Principle of original horizontality
layers of sediment that are generally deposited in a horizontal or nearly horizontal position
Radioactivity
the spontaneous decay of certain unstable atomic nuclei
Radiocarbon dating
a chemical analysis used to determine the age of organic materials based on their content of the radioisotope carbon-14
Radiometric dating
the procedure of calculating the absolute ages of rocks and minerals that contain radioactive isotopes
Relative dating
Rocks are placed in their proper sequence or order. Only the chronological order of events is determined
Law of superposition
in any undeformed sequence of sedimentary rocks, each bed is older than the one above and younger than the one below
Uniformitarianism
the concept that the processes that have shaped earth in the geologic past are essentially the same as those operating today, Charles Lyell's idea that geologic processes have not changed throughout Earth's history.