Biology of the Earth 2 - Chapter 11: Part 2 The Proterozoic...

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Chapter 11: Part 2
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The Proterozoic Eon
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The Proterozoic Eon Proterozoic : from the Greek work meaning “first life” The Proterozoic spanned ~2 billion years, from about 2.5 Ga to the beginning of the Cambrian Period 542 Ma The Proterozoic encompasses almost 1/2 of Earth’s history The Proterozoic received its misleading name before fossil organisms were discovered in Archaen rock!
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Proterozoic Eon During this time, Earth’s surface environment changed… From small, fast-moving plates, small continents, and an oxygen-poor atmosphere To a more familiar world of mostly large plates, large continents, and an oxygen-rich atmosphere
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Proterozoic Eon Changes to continents: New continental crust continued to form But at progressively slower rates By the middle of the Proterozoic, > 90% of Earth’s continental crust had formed Collisions between Archaen continents, accretion of new volcanic island arcs and hot spot volcanoes, resulted in the assembly of large continents Successive collisions brought together most of the continental crust on Earth into the first single supercontinent , named Rodinia , by around 1 Ga
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Proterozoic Eon Rodinia : first single supercontinent In this supercontinent construction, future Antarctica and Australia lay somewhere along the western coast of North America Sometime between 800 and 600 Ma, Rodinia broke apart Resulting in possibly a 2 nd , but short-lived, supercontinent called Pannotia
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Proterozoic Eon Atmospheric Changes: Transformation from oxygen- poor volcanic gas mix of Archaen, to oxygen- rich mix like today • However, present 21% O 2 concentration in today’s atmosphere did not occur until Phanerozoic Eon Atmospheric transformation evidence comes from studying Banded Iron Formation (BIF) Special kind of sedimentary rock containing alternating layers of Fe-Oxide minerals and Chert Deposition of BIF may have been triggered by an increase in the dissolved O 2 content of sea water
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Proterozoic Eon Atmospheric Changes: BIF : presence of oxygen in sea water could cause precipitation of Fe that had been soluble in sea water in the absence of abundant oxygen BIFs may have absorbed oxygen and kept atmospheric concentrations of gas low until ~1.8 Ga After then, oxygen concentrations in atmosphere appear to have increased substantially
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BIF: 2.1 Ga, weights 8.5 tons, found in NA
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Proterozoic Eon Oxygen-rich atmosphere permitted great diversification of life and eventual migration over land by living organisms Life could become more complex because aerobic metabolism (oxygen-dependent) is much more efficient than anaerobic metabolism (oxygen-free) Oxygen provided raw material from which ozone (O 3 ) forms Ozone protects the land surface from harmful ultraviolet rays
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Proterozoic Eon Last 1/2-billion years of Proterozoic saw transition from simple organisms into complex ones Prokaryotic organisms : single cells, do not contain a nucleus Eukaryotic cells
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This note was uploaded on 04/01/2012 for the course GEOLOGY 1122 taught by Professor Sethrose during the Fall '10 term at Georgia State University, Atlanta.

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Biology of the Earth 2 - Chapter 11: Part 2 The Proterozoic...

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