Chapter 21 - Geologic Time Scale Flashcards
Record of earth’s history from its origin (4.6 bya) to present.
Geologic time scale
Longest time unit in the geologic time scale.
Eon
Informal unit of geological time consisting of the first 3 Eons, during which earth formed and became habitable
Precambrian
Second longest time unit in the Geologic Time Scale
Era
Third longest time unit in the Geologic time scale
Period
Time unit in the Geologic time scale, smaller than a period.
Epochs
The theory that geological processes occurring today have been occurring since the earth formed.
Uniformitarianism
The age of an object in relation to the ages of other objects
Relative age dating
The law that a sedimentary rock layer is older than the layers above it and younger than the layers below it if the layers are not disturbed
Superposition
A fault or body of rock is younger than any other body of rock that it cuts though
Cross cutting relationships
States that fragments, called inclusions, in a rock layer must be older than the rock layer that contains them
Principle of inclusions
A break in the geologic record due to rock layers weathering or sediment not depositing for a long period.
Unconformities
The matching of rock outcrops to fossils exposed in one geographic region to similar outcrops or fossils exposed in other geographic regions.
Correlation
A rock or sediment layer that serves as a time marker in the rock record.
Key-bed
States that sedimentary rocks left undisturbed will remain in horizontal layers
Original Horizontaliry
