Outline #6 Stratigraphy and Geologic Time

A) Literal Biblical interpretation (1654 - Archbishop James Usher)
-Catastrophism

B) Principal of uniformitarianism (James Hutton, 1785)
-"the present is the key to the past"
-The laws of nature do not change with time.
-The Earth has evolved by uniform, gradual processes over an immense span of time.
-Sir Charles Lyell (1797-1875) Principles of Geology (process rates do not change)
-Charles Darwin (1809-1882) Origin of Species by Natural Selection

C) Early estimates of geologic time based on quantitative data:
1) salinity of the oceans
2) thickness of sediment
3) heat loss from the earth

II) Relative Dating
-determining the chronologic order of a sequence of events
Relative dating is accomplished by applying the principles of stratigraphy

A) Principles of Stratigraphy
1) the principle of superposition (Nicolaus Steno, 1669)
-we must assume that:
i) rock layers were horizontal when they were deposited.
ii) the rocks have not been so severely deformed that the beds are overturned.
2) the principle of faunal succession
3) the principle of crosscutting relations
4) the principle of inclusions

C) Breaks in the Stratigraphic Record (Unconformities and hiatuses)

-An unconformity is a substantial break or gap in a stratigraphic sequence that marks the absence of part of the rock record
-A hiatus is the lapse in time recorded by an unconformity

1) Angular unconformity
2) Disconformity
3) Nonconformity

III) The Geologic Time Scale
-using the principles of superposition and faunal succession, geologists have determined the chronologic sequence of rocks throughout broad regions of the world and have constructed a standard geologic time scale.

-Rock units are distinguished from each other by major changes in rock type, unconformities, or abrupt vertical changes in the fossil groups they contain.

-Divided into geologic time units which are used worldwide: eons, eras, periods, and epochs.