Chapter 11 Notes

Chapter 11 Notes - Chapter 11: The Dynamic Planet The Pace...

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Chapter 11: The Dynamic Planet The Pace of Change o Geologic Time Scale – summary timeline of all Earth history Reflects currently accepted names of time intervals for each segment of Earth’s history Vast Eons Briefer Eras, Periods, and Epochs Present thinking Earth’s age = 4.567 billion years Moon’s age = 30 million years younger Depicts two important kinds of time: Relative – what happened in what order o Sequence of events o Based on relative positions of rock strata above or below each other o Based on important general principal of superposition rock and sediment always are arranged with the youngest beds “superposed” toward the top of a rock formation and the oldest at the base, if they have not been disturbed Study of these sequences is called stratigraphy o Relative time places Precambrian (beginning) at bottom of time scale and Holocene (today) at the top Fossils (the remains of ancient plants and animals serve as important time clues. Absolute – actual number of years before present o Determined by radiometric dating o Actual millions of years ago shown on time scale o Permit scientists to actively update geologic time and refine the time scale sequence lending to greater accuracy to relative dating sequences Holocene – youngest epoch on geologic time scale Postglacial conditions since retreat of continental glaciers the last 11,500 years Because of impact of human society on planetary systems, discussion is underway about designating new name for human epoch o Possibly Anthropocene o Uniformitarianism Assumes that the same physical processes active in environment today have been operating throughout geologic time. o Catastrophism Places vastness of Earth’s age and complexity of its rocks into a shortened time span Holds that earth is young and that mountains, canyons, and plains formed through catastrophic events that did not require eons of time More appropriately considered a belief than a serious scientific hypothesis
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Earth’s Structure and Internal Energy o Condensed and congealed from nebula of dust, gas, and icy comets about 4.6 billion years ago Oldest surface rock discovered on earth – Acasta Gneiss was found in northwestern Canada – radiometrically dated to age of 3.96 billion years. Recent search found derital zircons in Western Australia dating to about 4.3 billion years old – possibly oldest materials in Earth’s crust. These discoveries tell us that Earth was a forming continental crust at least 4 billion years ago, during Archeon Eon. o As earth solidified, gravity sorted materials by density. Heavier substances such as iron gravitated slowly to its center, and lighter elements such as silica slowly welled upward toward the surface and became concentrated in crust Earths interior is sorted into roughly concentric layers Internal Differentiation o Cooler areas generally are more rigid and transmit
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Chapter 11 Notes - Chapter 11: The Dynamic Planet The Pace...

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