5 billion years ago oxygen crisis 2 billion years ago

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Photosynthesis – 3.5 billion years ago Oxygen crisis – 2 billion years ago Evolution of eukarya – crucial first step Eukarya evolved by infoldings of membranes that lead to cell nucleus and a large ancestral host cell absorbed smaller prokaryotes with specialized functions (symbiotic relationship ) Mitochondria: cell organs in which oxygen helps produce energy (by making molecules of ATP) Chloroplasts: structures in plant cells that produce energy by photosynthesis Fossil evidence for complex multicellular life – 1.2 billion years ago Phyla: animals are grouped by body plan Cambrian explosion – 545 million years ago and spanned 40 million years Oxygen reached a critical level, evolution of genetic complexity, climate change, and absence of efficient predators Plants were the first large organisms to develop the means to live on land – 475 million years ago Within about 75 million years, amphibians and insects were eating land plants By the beginning of the Carboniferous period (360 billion years ago), vast forests and abundant insects thrived around the world Conclusion: The Cambrian explosion was crucial and plants and animals migrated onto land. Why was the rise of oxygen so important to evolution? Ignited an explosion of eukaryotic diversification Oxidation reactions: chemical reactions that remove oxygen from the atmosphere Oxygen atmosphere came from cyanobacteria (2.7 billion years ago) Oxygen buildup 2.35 billion years ago Cambrian Explosion occurred when earth was 4 billion years old Conclusion: Oxygen leads to explosion of diversification. Did an impact kill the dinosaurs? Cretaceous and Tertiary periods – 65 million years ago Alvarez & Alvarez discovered K-T boundary – rich in iridium Extinction of dinosaurs was caused by impact of an asteroid or comet
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Mass extinction Impact evidence: high abundances of metals, grains of shocked quartz, spherical rock droplets, and soot Shower of red-hot debris ignited fires and killed many living organisms Impact caused chemical reactions in atmosphere that produced large quantities of
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