Earth History

Topics: Geology, Fossil, Geologic time scale Pages: 2 (452 words) Published: November 22, 2011
Geologic Time:
Geology needs a time Scale:
-The prime goal of the science of geology, is to interpreting earth history. Geological time scale-
-Anordered,internallyconsistent, internationally recognized sequence of time intervals, and record the life of Earth. Short history of geology:
James Ussher(mid 1600s)- he determined that earth was only a few thousands of years old having been created in 4004 b.c Catastrophists(17-18cen.)-believed that earth landscape had been developed primarily by great catastrophes. John Wesley Powell(1869)-

He realized that the evidence for an ancient earth is concealed in its rocks. Geologists-who concern w/ the studied the earth history ,they learned that earth is much older than anyone and its surface and interior have been changed over and over again. birth of modern geology:

Uniformitarianism-It simply state that the physical, chemical, and biological laws that operate to day have also operate in the geologic past. Relative dating-key principles:
Types of dates used to interpret Earth
1.RelativeDates-meansput events in their proper sequence of formation. 2.Numerical dates-which pinpoint the time in years when an event took place. Basic Principle or rules that can be established in relative dates: Law of superposition:

-It simply states that in an underformedsequence of sedimentary rocks, each bed is older than the one above it and younger than one below. Principle of original horizontality:
-It means that layers of sediment are generally deposited in a horizontal position. Principleofcross-cutting relationship:
-An intrusive rock body is younger than the rocks it intrudes. A fault is younger than the rock layers it cuts. Inclusions:
-are pieces of one rock unit that are contained within another. Sometimes it can aid the relative dating process. Unconformities:
-all such breaks in the rock record are termed”unconformities”. “3 basic types of unconformities:”
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