chapter17 - 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 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 -rock, metal, ice -most < 3 km diameter -velocity: 20 km/s -ice , rock -most < 15 km -velocity: 60-70 km/s
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Asteroid belt: the source of asteroids NASA/Goddard Space Flight Center chunks of rock that did not coalesce into planet when solar system formed Some are pulled out of orbit by 1) collision with another asteroid or 2) gravitational influence from sun/planets
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The Oort Cloud: the source of comets http://solarsystem.nasa.gov/planets/images/inset- oortcloud-large.gif Oort cloud – vast spherical region extending more than 100,000 times Earth’s distance from sun, containing billions of comets
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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? As bolides enter atmosphere, friction causes heating Emits heat, visible light ( fireball, shooting star ) Small bolides (“meteoroids”) burn up in upper atmosphere or are slowed down enough to free fall to Earth Larger bolides (>10 tons) are not completely slowed down and retain
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This note was uploaded on 09/11/2011 for the course GEO 107 taught by Professor Stidham during the Spring '08 term at SUNY Stony Brook.

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chapter17 - Ch. 17 Outline-Impacts and Mass Extinctions...

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