17-Geologic_Time - Geologic Time Relative and Absolute...

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Geologic Time Relative and Absolute Dating of Rock Sequences, and the Importance of Fossils Mark Leckie - Department of Geosciences mleckie@geo.umass.edu
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Understanding the history of life on Earth requires a grasp of the depth of time and breadth of space . Establishing chronologies, both relative and absolute, and geographic change over time are essential for viewing the motion picture that is the history of life on Earth. http://evolution.berkeley.edu/evosite/lines/IIIdistribution.shtml
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• Meteorites and oldest moon rocks are 4.6 billion years old 4,600,000,000 years (i.e., the age of the solar system) • Oldest minerals found so far on Earth are zircon grains from a sandstone in western Australia, dated at 4.4 billion years old! • The oldest known rocks on Earth are 3.96 billion years old, from the Northwest Territories of Canada. Why the difference between age of the solar system & oldest rocks on Earth? How old is the Earth? How do we know? This just in: Oldest rocks recently found near Hudson Bay, Canada: 4.28 billion year old mafic crust!
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The Earth has changed greatly over geologic time: • Nature of the crust • Pace of tectonics • Evolution of life • Composition of our atmosphere
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What processes have helped to shape Earth history? Many natural events: • meteorite impacts • formation & destruction of ocean basins 2 -rich atmosphere
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All of these natural events are still going on today - We see evidence in the rock record that these events have been occurring for a long time. Geologists call this uniformitarianism . The physical laws governing the universe operate uniformly through time. James Hutton (1726-1797): “The results, therefore, of our present inquiry is, that we find no vestige of a beginning – no prospect of an end .”
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Uniformitarianism • slow, gradual, continuous change • vast time (“deep time”) • Hutton’s views were championed by Charles Lyell (“father of modern geology”) published 3-volume “Principles of Geology” in 1833 dismissed the role of “catastrophy” in shaping Earth history • important influence on Charles Darwin
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are not occurring today : • huge meteorite impacts mass extinctions of organisms (well, maybe) abrupt climate change (well, maybe!) ice sheets in the tropics(?) •some types of deposits (e.g., banded iron formations or vast coal deposits) • also, rates of processes have varied through time (e.g., plate tectonics, sea level or climate change, evolution) The geologic record shows us that Earth history is not exclusively driven by slow, gradual, uniform change. Catastrophic and rapid events have been important!
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This note was uploaded on 11/22/2011 for the course BIOLOGY 190a taught by Professor Staff during the Fall '11 term at UMass (Amherst).

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17-Geologic_Time - Geologic Time Relative and Absolute...

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