Popular in Geol 113-2
Popular in Geology
This 3 page Class Notes was uploaded by Katie Thedford on Monday September 26, 2016. The Class Notes belongs to 20841 at Fort Lewis College taught by Allie Jackson in Fall 2016. Since its upload, it has received 3 views. For similar materials see Geol 113-2 in Geology at Fort Lewis College.
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Date Created: 09/26/16
Geologic Time Dating, correlations, and clues Bishop James Ussher calculated age of earth based on biblical genealogies o mid-1600’s o earth created October 23, 4004 B.C. o Most people believed this date and believed that earth’s landscapes and rocks were created by large catastrophes o Catastrophism was the main doctrine James Hutton observed his surroundings and wrote a bold publications in the late 1700’s o Siccar point Scotland – the famous angular unconformity o Uniformitarianism o These views require a very long history for earth o This was gradually accepted by the scientific community- still not universally accepted o But – catastrophes do happen but they only explain a small portion Relative age dates- o Placing rocks and geologic events in their proper sequence Numerical dates- o Define the actual age of a particular geologic event (termed absolute age dating) Principles of relative Dating: Principle of original horizontality o Layers of sediment and many volcanic flows are originally deposited in horizontal layers Principle of superposition o Younger sedimentary or volcanic rocks are deposited on top of older units Principle of inclusions o A younger rock can contain pieces of an older rock o xenoliths are fragments of older igneous rock incorporated into younger igneous rock Principle of cross- cutting o Younger features or rocks can cut across younger features or rocks Principle of original continuity o Sediments are regionally deposited in continuous sheets Principle of baked contacts o Igneous intrusions metamorphose surrounding rock o Surrounding rock that was baked must be older than the metamorphosed intrusions Fossils are… o Any remains, imprints or traces of a plant or animal preserved in a rock or deposit o Can be skeletal remains, mineral replacements, casts and molds, carbon films, impressions Principle of faunal succession o Fossils change in different ages and layers of rock 2 o There is a systematic progression of fossils through time o Assume basic ideas about extinctions and evolution is correct Unconformities o A break in the rock record caused by a break in the rock record produced by an erosion or non- deposition o Types: Angular unconformity- Tilted rocks overlain by flat-lying rocks Disconformity Strata on either side of the unconformity are parallel but time is loss Nonconformity Sedimentary rock lies above and was deposited on the pre-existing and eroded metamorphic or igneous rock. 3