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Add to table of contents:. Review Pg. 50 Evidence of Impact Pg. 51. Hypothesis: Meteor Impact-. It is widely agreed that a meteor-- 10 kilometers across - struck just off the coast of the Yucatan peninsula 65 million years ago.

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  1. Add to table of contents: Review Pg. 50 Evidence of Impact Pg. 51

  2. Hypothesis: Meteor Impact- • It is widely agreed that a meteor-- 10 kilometers across - struck just off the coast of the Yucatan peninsula 65 million years ago. • Caused dense clouds of dust to block the sun's rays, darkening and chilling Earth to deadly levels for most plants and, in turn, many animals. Then, when the dust finally settled, greenhouse gases created by the impact caused temperatures to skyrocket above pre-impact levels. • In just a few years, according to this hypothesis, these frigid and sweltering climatic extremes caused the extinction of not just the dinosaurs, but of up to 70 percent of all plants and animals living at the time.

  3. Evidence for the Asteroid Impact Hypothesis • 1. Impact CraterMeteor traveling 30 kilometers per second -- 150 times faster than a jet airliner. Scientists have concluded that the impact that created this crater occurred 65 million years ago. The datecorresponds perfectly to the date of the dinosaur extinction.

  4. Evidence for the Asteroid Impact Hypothesis • 2. Rare MetalThe metal iridium, which is similar to platinum, is very rare on Earth's surface but is more common in asteroids and in molten rock deep within the planet. Scientists have discovered levels of iridium30 times greater than average in the Cretaceous/Tertiary (KT) boundary, the layer of sedimentary rock laid down at the time of the dinosaur extinction. The piece of clay, held by Walter Alvarez, that sparked research into the impact theory. The greenish-brown band in the center is extremely rich in iridium.

  5. Evidence for the Asteroid Impact Hypothesis • 3. Impact Ejecta Pieces of once-molten rock, called impact ejecta, are evidence of an explosion powerful enough to instantly melt bedrock and propel it more than a hundred miles from its origin. Ranging in size from chunks to tiny beads, impact ejecta are common at the Cretaceous/Tertiary (KT) boundary, the geological layer that defines the dinosaur extinction. Form a layer half a meter a thick at K/T boundary in Haiti.

  6. Evidence for the Asteroid Impact Hypothesis • 4. Fractured CrystalsCrystals, often called "shocked quartz," show a distinctive pattern of fracturing caused by high-energy impacts or explosions. Scientists maintain that the fracture pattern in these quartz crystals could only have been caused by a massive meteor impact. The high-energy impact pattern is prevalent in quartz found at or near the Cretaceous/Tertiary (KT) boundary, the geological layer deposited at the time of the extinction.

  7. 5. Fossil RecordPaleontologists see evidence in the fossil record that dinosaurs were doing quite well prior to the end of the Cretaceous -- that they were in no way declining in abundance when the impact occurred. • A sudden "now you see them, now you don't" end to the dinosaurs implies a catastrophic cause. Depending on location and interpretation, the fossil record seems to say different things.

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