F13 quiz 1 condensed notes

Indeed a single tree can encompass all of life as we

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Unformatted text preview: s easily detected in the rocks, due to the “invention” of hard parts, did not appear until about 0.54 billion years ago, the beginning of the Cambrian Period. Interestingly, Precambrian rocks are found exclusively on continents; all oceanic rocks are younger. On the continents, Precambrian rocks today are often covered by younger sedimentary deposits. An unconformity is a buried surface of erosion. We can consider the amount of time during which erosion occurred, as well as the time represented by the rock that was removed, as “missing time” from the geologic record. When Precambrian rock lies beneath an unconformity, it is often called “crystalline basement.” Precambrian shields (not to be confused with shield volcanoes), in which Precambrian rocks crop out on the Earth surface, are located on every continent. They are areas of great size (the Llano Uplift here in Texas is too small to be a shield), and low elevation. Rocks in shields often feature signs of great deformation, evidence that at some point in the past they were the scenes of violent activity. Nowadays, however, shield regions are exceptionally stable. They are excellent exploration grounds for ore deposits (metals, diamonds), but not for oil. LECTURE 9: ORIGIN OF LIFE ON EARTH The histories of life and of the Earth are inextricably intertwined; one can’t be understood without the other. Life can be considered as...
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This document was uploaded on 03/03/2014 for the course GEO 303K at University of Texas at Austin.

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