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Class 9 : The K-T impact (the Alvarez theory)

Class 9 : The K-T impact (the Alvarez theory). Geological anomalies at K-T boundary. The K-T crater. Timeline for devastation. I : Geological anomalies at the K-T boundary. Detailed investigation finds the following in the K-T transition layers… Iridium

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Class 9 : The K-T impact (the Alvarez theory)

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  1. Class 9 : The K-T impact(the Alvarez theory) • Geological anomalies at K-T boundary. • The K-T crater. • Timeline for devastation.

  2. I : Geological anomalies at the K-T boundary

  3. Detailed investigation finds the following in the K-T transition layers… • Iridium • In the K-T boundary everywhere in world! • Higher levels of iridium in North America. • Large impact or volcanism (e.g. Deccan Plateau). • Shocked quartz • Find very strongly shocked quartz. • Such quartz only thought to be found in impact sites. • Find more weakly shocked quartz in obvious volcanic sites. • Soot – and lots of it!

  4. Feldspar spherules • Found spread throughout the KT boundary. • Formed as vaporized minerals started to recondense. • No known volcano can spread such spherules across the whole globe.

  5. II : The K-T crater

  6. Coastline Cenotes

  7. Seismic reflections

  8. Alvarez theory given huge boost by discovery of the Chicxulub crater: • Circular crater revealed through pattern of cenotes (small sinkholes). • Crater confirmed by detection of gravitational anomalies. Also measured by seismic reflections. • Crater is ~150 km diameter. • Exactly the kind of crater predicted by the Alvarezes. • Crater dated at 65 Myr.

  9. Zircon

  10. Zircon dating • Zircon is a mineral (containing mainly zirconium) that contains some uranium. • Uranium decays into lead. • There are two isotopes of uranium (U-235 and U-238) that decay radioactively into two isotopes of lead (Pb-207 and Pb-208). • This gives us two independent “clocks” (both based on radioactivity)… • Gives us enough information to determine the age of zircon crystal despite possibility of partial lead loss due to heating. • See page 117 of textbook.

  11. III : Timeline for devastation

  12. Initial impact of a 10km asteroid or comet • Atmosphere has almost no effect on incoming object… strikes surface at full speed. • Explosive yield of approximately 100 million megaton TNT equivalent. • Impacting asteroid and approx 100 km3 of Earth rock are vaporized and thrown 100 km into the atmosphere. • Intense fireball and blast wave flattens and ignites everything for 1000s of km across. • Molten debris rains down across planet, seeding massive wildfires – 90% of all plant life burns. • Huge earthquakes cause massive Tsunamis… devastate coastlines around the globe.

  13. Next 10-1000 years… • Atmospheric debris and smoke completely blocks the Sun from reaching the surface. • Temperature plummets (like “nuclear winter”). • Photosynthesis stops and most plants die. • Food chain collapses. • Eventually, debris settles out of atmosphere and the Sun starts to shine again… • But then there’s dramatic global warming… • Carbon dioxide from fires causes a greenhouse effect… temperature rises and planet becomes too hot! • This lasts for an unknown length of time… • Few species survive this ordeal…

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