Chapter 6 Book Notes

Impact evidence high abundances of metals grains of

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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 harmful compounds Conclusion: With dinosaurs gone, mammals became new animal kings of planet and evolved. Did impacts cause other mass extinctions? Impacts like the K-T should happen every 100 million years or so Most impacts occur in oceans Mutation rate might spike upward during magnetic reversal time due to the absence of normal protection from high-energy particles Supernova – explosion of massive stars. When one occurs near earth, we might expect a big upward spike in the number of cosmic rays reaching Earth and causing mutations. Gamma rays – destroy Earth’s ozone layer Conclusion: Magnetic reversal, supernovas, and gamma rays are the hypotheses. Is there a continuing impact threat? Meteors – burns up and heats the surrounding air Conclusion: Many known asteroids have orbits around the Sun that cross Earth’s orbit or pass near enough to Earth’s orbit that they may someday be gravitationally perturbed into an Earth-crossing orbit and hit us. How did we evolve? Hominids (human ancestors) 6 and 7 million years ago Neandertals disappeared 30,000 years ago Homo floresiensis – lived on an Indonesian island 12,000 years ago Conclusion: The fact that modern gorillas, chimps, and humans all evolved from the same ancestor shows that relatively small genetic differences can make a big difference in species success and that evolution of intelligence is a complicated process. Are we still evolving? Cultural evolution: changes that arise from the transmission of knowledge accumulated over generations Technological revolution Conclusion: Advanced civilizations can alter the course of evolution through their choosing, rather than remaining subject to the random processes of natural selection. How might we create artificial life? Top-down approach: rearrange bits and pieces of existing organisms OR try to build an extremely simple living cell in the lab (RNA) Conclusion: Top-down and bottom-up approaches.
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