17.2- Relative Age Dating Flashcards
How old is the Earth?
4.6 bya
Who figured out how old the Earth was?
James Hutton
Uniformitarianism
the theory that geologic processes occurring today have been occurring since Earth formed
one of the basic foundations of geology
Relative Age
the age of an object in relation to the ages of other objects
indicates that one rock is older than another rock but does not give an age in years
Original Horizontality
states that sedimentary rocks left undisturbed will remain in horizontal layers
states that sedimentary rocks are deposited in horizontal layers ALWAYS
Superposition
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
Cross Cutting Relationships
the principle that a fault or body of rock is younger than any other body of rock that it cuts through
Principle of Inclusions
the principle that fragments, called inclusions, in a rock layer must be older the rock layer that contains them
Unconformities
a break in the geologic record created when rock layers are eroded or when sediment is not deposited for a long period of time
doesn’t form until the eroded surface is covered
Correlation
the matching of a rock outcrops or fossils exposed in one geographic region to similar outcrops or fossils exposed in other geographic regions
Key Bed
a rock or sediment layer that serves as a time marker in the rock record
Index Fossils
a fossil that is used to establish the age of rock layers because its distinct, abundant, and widespread and existed for only a short span of geologic time
Index fossils must meet these requirements
1) Fossil must be present in rocks scattered over a large region
2) Fossil must have features that distinguish it from other fossils
3)The organisms from which the fossil formed must have lived during a short span of geologic time
4) The fossil must occur in fairly large numbers within the rock layers
