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GLG102 Summary Test 2

GLG102 Summary Test 2 - Chapter 9 The crust-forming...

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Chapter 9 The crust-forming processes that yielded Archaen granite-gneiss complexes and greenstone belts continued into the Proterozoic but at a considerably reduced rate. Paleoproterozoic collisions between Archean cratons formed larger cratons that served as nuclei, around which crust accreted. One large landmass so formed was Laurentia, consisting mostly of North America and Greenland. Paleoproterozoic amalgamation of cratons, followed by Mesoproterozoic igneous activity, the Grenville orogeny and the Midcontinent rift, were important events in the evolution of Laurentia. Ophiolite sequences marking convergent plate boundaries are first well documented from the Neoarchean and Paleoproterozoic, indicating that a plate tectonic style similar to that operating now had become established. Sandstone-carbonate-shale assemblages deposited on passive continental margins were very common by Proterozoic time. The supercontinent Rodinia assembled between 1.3 and 1.0 billion years ago, fragmented and then reassembled to form Pannotia about 650 million years ago, which began fragmenting about 550 million years ago. Glaciers were widespread during both the Paleoproterozoic and the Neoproterozoic through the Proterozoic. Photosynthesis continued to release free oxygen into the atmosphere, which became increasingly rich in oxygen through the Proterozoic. Fully 92% of Earth’s Iron ore deposits in the form of banded iron formations were deposited between 2.5 and 2.0 billion years ago. Widespread continental red beds dating from 1.8 billion years ago indicate that Earth’s atmosphere had free oxygen for oxidation of iron compounds. Most of the known Proterozoic organisms are single-celled prokaryotes (bacteria). When eukaryotic cells first appeared is uncertain, but they were probably present by 1.2 billion years ago. Endosymbiosis is a widely accepted theory for their origin. The oldest known multi-celled organisms are probably algae, some of which might date back to the Paleoproterozoic. Well-documented multi-celled animals are found in several Neoproterozoic localities. Animals were widespread at this time, but because all lacked durable skeletons their fossils are not common. Most of the world’s iron ore production is from Proterozoic banded iron formations. Other important resources include nickel and platinum. Chapter 10 Most continents consist of two major components: a relatively stable craton over which epeiric seas transgressed and regressed, surrounded by mobile belts in which mountain building took place. Six major continents and numerous microcontinents and island arcs existed at the beginning of the Paleozoic Era; all of these were dispersed around the globe at low latitudes during the Cambrian.
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