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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