Earth History

“EARTH HISTORY” 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 history 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:” 1. Angular unconformity- it consists of tilted or folded sedimentary rocks that are overlain by younger, more flat-lying strata. 2. Disconformity-are more common but usually far less conspicuous, because the strata on either side are essentially parallel. 3. Nonconformity-the break separates older metamorphic or intrusive Igneous rocks from younger sedimentary strata.

Correlation of rock layers: -The matching up of two or more geologic Phenomena in different areas. FOSSILS: EVIDENCE OF FAST LIFE -The remains or traces of prehistoric Life. Types of fossils: *mold fossils (a fossilized impression made in the substrate) *cast fossils (formed when a mold is filled in) *trace fossils (fossilized nests, gastroliths, burrows, footprints, etc. ) *true form fossils (fossils of the actual animal or animal part). Fossils and correlation: Principle of fossil succession-states that fossil organisms originate, coexist, and disappear from the geologic record in a definite sequential order.

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