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chapter17_post - Ch 17 Outline-Impacts and Mass Extinctions...

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Ch. 17 Outline--Impacts and Mass Extinctions Projectiles from space Large: “Bolides” (Asteroids and Comets) Small: Meteroids What happens when bolides reach Earth and impact a rocky surface (the impact process) Evidence of impacts on Earth • Crater • Shattercones • Shocked minerals (such as quartz) • Glass beads of impact melt • Layers of soot, from fires • Iridium Impact sites on Earth Effects of impacts on Earth Fires and shockwave Earthquakes and volcanism Global atmospheric effects induce climate change and mass extinctions Example: the Chicxulub impact and extinction of dinosaurs Tracking bolides Defensive strategies
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Projectiles from Space 1. Asteroids 2. Comets
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Asteroid belt NASA/Goddard Space Flight Center
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Comets and the Oort Cloud http://solarsystem.nasa.gov/planets/images/inset- oortcloud-large.gif http://www.st- andrews.ac.uk/~bds2/ltsn/ljm/JAVA /COMETORB/COMET.HTM
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Asteroids and Comets (“bolides”) • Asteroids are chunks of rock that did not coalesce into planet when solar system formed • Some asteroids are pulled out of normal orbits by asteroid collisions or gravitational influence of sun and planets • Comets consist of ice and some rock • Comets come from the Oort cloud and have highly elliptical orbits • Comets spray off water and dust to form glowing tails w hen hit by solar wind • Comets eventually lose all their water and become rocky • Asteroids and comets occasionally cross paths with Earth
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What happens when bolides reach Earth?
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chapter17_post - Ch 17 Outline-Impacts and Mass Extinctions...

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