lecture15 - The History of Earth and Life Lecture 15 1...

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The History of Earth and Life Lecture 15 1 Lecture 15 - Proterozoic Geology The Proterozoic 2.5 billion to 545 million years ago (nearly 2 billion years) About half the length of the recorded history of the earth Many important events occur during the Proterozoic Normal plate tectonics operates (the bulk of the North American craton accretes) Major changes occur in the composition of the atmosphere: CO 2 content decreases and O 2 content increases (these changes affect both the climate and life) Life changes greatly as metabolism changes, eukaryote cells evolve, and sexual reproduction becomes widespread Three major divisions of Proterozoic time Early Proterozoic (2.5–1.8 billion years ago) Mid Proterozoic (1.8–1 billion years ago) Late Proterozoic (1 billion –545 million years ago) Early Proterozoic (2.5–1.8 billion years ago) The northern part of the American craton was compiled Most banded iron formations formed Climate varied as CO 2 was withdrawn from the atmosphere (more continental crust became available for weathering) Oxygen became a significant component of the atmosphere at the end of the Early Proterozoic A major glaciation occurred Early Proterozoic: Normal Plate Tectonics Established The growth of the North American craton Greenstone Belts are small comparing to Archean Greenstone Belts Plate collisions represent modern large-scale plate activity. Example: Wopmay Orogen Example of "modern" plate tectonics in the Early Proterozoic Sediments on a passive continental margin A rifted passive continental margin developed The ocean basin closed by subduction A microcontinent collided with the Slave Craton A deformed mountain belt formed Atmospheric Change During the Early Proterozoic Atmosphere Changes No oxygen to speak of in the atmosphere until 2.3 billion years ago
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lecture15 - The History of Earth and Life Lecture 15 1...

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