Earth 125 1st Edition Lecture 21 Outline of Last Lecture I. Human Evolutiona. Causes of ExtinctionOutline of Current Lecture II. Human EvolutionCurrent LectureI. The K/T event1. Meteorite Impact at K/Ti. Evidence:1. Iridium anomaly2. High temperatures3. Shocked Quartz4. Tektites2. Crater in Arizona – 1 mile across, 550 feet deepi. Is this the “smoking gun” of K/T?1. Unfortunately not. It’s too small2. Impact was from 50,000 years agoa. We need evidence from much before this3. Size of meteor that produced the crater: about 150 feetii. The chance of finding a crater from 65 MY ago are very slimiii. Yucatan, Mexico: Chicxulub1. Hidden by erosion2. 65 million years agoa. Hole must be into rocks that are older than 65 myab. Cross-section of crater reveals a sequence of layered rocks of Cretaceous age and youngeri. Shows exactly what one would expect from a “hole” punched in by an impact and filled in by the debris falling back into the crater3. Distribution of tektites are largest near Yucatan4. Evidence of impact is non-controversialiv. Good analogy between Nuclear War and what happened at K/T3. Effect of K/T impacti. Instantaneousii. Locally: terrible destruction1. Earthquake, fires, etc. 2. comets and asteroids move at high speeds3. shockwave (1000km/s winds)4. fireball – wildfires a. Evidence: charcoal layer in many parts of N. America5. Magnitude 10+ earthquake & tsunamisa. evidence: tsunami deposits throughout Caribbean and Gulf of Mexicoiii. Dust from the impact, and smoke from fires, blanketed the Earth and blocked the sunlight1. Evidence of dust: drilling ship can send a drill string to the ocean floor and recover core2. Effects on time scale of months to years: “Nuclear Winter”a. ejecta chokes atmosphere (“dust-loading” b. blocks sunlight and photosynthesis (damages/kills food-chain)c. coolingd. Calcium carbonate/limestone created carbon dioxide (greenhouse gas)3. Long term effects 10s-1000s years: global warming4. If the K/T extinction was caused by a “large rock” from the sky, is it plausible that other extinctions may have had similar causes?i. Are impacts common?1. The moona. Impacts are quite common, but most are small. Only few are large.b. Age of moon: approximately 4 billion
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