Geology 1003 notes (4)

Geology 1003 notes (4) - Geology Notes(3 I Proterozoic A...

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Geology Notes (3) I. Proterozoic (3-11-08) A. Building of Laurentia 1. Rodinia is a supercontinent by 1 billion years 2. Grenville Orogeny 3. second supercontinent by 550 million years a. significant because it was situated right over the south pole, making the largest global glaciation before this time period B. Precambrian Life: 1. Archean: 3.8 billion years: there are carbon spheres in Greenland in sediment a. enriched in carbon 12 2. 3.5-3.2 billion years: the first body fossils of organisms in Australia are found 3. 3.5 billion years: the first stromatolites are found a. Structures produced by bacterial masses; shallow marine structures produced by cyanobacteria (photosynthesizes) b. Live today in hypersaline seawater environments and areas where there’s a large tidal range 4. Archean, there are only prokaryotes, but in the Proterozoic, things change a. 2.7 billion years: biomarkers which represent the existence of eukaryotes are found b. Sterane: chemical produced by eukaryotes 5. first real fossil of a eukaryote belonged to a protest a. was the fossil of a single cell green algae (producer) called Acritarchs b. it is not clear how they are related to present day green algae 6. stromatolites become very diverse, but they also become almost extinct at the end of the Proterozoic a. Why? Because animals (consumers) appeared on the scene in the last 30 million years of the Proterozoic b. Ediacara Fauna: soft bodies whose fossil records are generally trace fossils:
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c. jellyfish, worms, arthropods, mollusks (clams), and sponges also appear 7. the first fossil skeleton is of a calcium carbonate tube C. Precambrian Climate: 1. 2.9 billion years: first glacial deposits of tillite in the late Archean 2. early Proterozoic marks the first global glaciation 3. the late Paleozoic (900-600 million years) is the most extreme superglaciation we’ve known in Earth’s history a. The entire earth was covered in ice (?) i. hypothesis is called “snowball earth” ii. ice has a high albedo, so light is reflected into space and isn’t turned into heat, so the Earth’s temperature drops 4. warming from volcanic release of carbon dioxide in the atmosphere begins to warm up the earth 5. atmosphere in the Precambrian: a. high levels of CO2, low levels of oxygen (produced by photosynthesizes) b. there’s 3 forms of iron: Fe metal, Fe 2+, and Fe 3+ i. early oceans contained lots of Fe 2+, but if it sees oxygen if forms Fe 3+ oxides (iron oxides) ii. iron precipitated out of sea floor vents and oxygen accumulates in the atmosphere c. BIF: banded iron formations
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Geology 1003 notes (4) - Geology Notes(3 I Proterozoic A...

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