EARTH 7 Lecture 13: Earth 7 Lecture 13
Impact hypothesis
- 1980 walter and luis alvarez (ucb) proposed that 10km diameter asteroid struck the earth
causing the mass extinction
Evidence for impact
1. Worldwide iridium spike
a. Iridium: rare on Earth, more abundant in meteorites and cosmic dust
b. Iridium at 30x normal rate of accumulation
2. Tektites
a. Glassy globules of earth’s crust that melted in the blast and quickly hardened as
they rained down over large areas of Earth
3. Shocked quartz in Caribbean
a. Quartz that has been subjected to the sudden application of extreme pressure
4. Tsunami deposits and evidence of huge landslides around caribbean
Still, as late as 1988, more than half of all American paleontologists contacted in a survey
continued to believe that the extinction of the dinosaurs was in no way related to an impact
→ uniformitarianism (look at processes occurring today, use simple gradual processes to explain
big things on earth) and catastrophism
5. The smoking gun (1991)
- Chicxulub crater, mexico ~ 200-300km diameter crater dated to 66Ma
- Impactor must have been 10km
- Today, crater buried under >1km of cenozoic sedimentary rock
- Complicated discovery history (1st evidence was geophysical data from all
researchers) but lots of shocked quartz and presence of K-Pg boundary was the
clincher (reported in 1991)
Shoemaker Levy 9 Hits Jupiter in 1994
- Even after Chicxulub crater is found in 1991 many scientists still doubt that it would be
devastating enough to cause a mass extinction
- Soon after, a natural test arises:
- Comet headed for jupiter
- Impact began on july 16 1994 and lasted for a week
- Just one of the many fragments struck with a force about 100x greater than all the
nuclear weaponry in existence, and created impact scar larger than earth
Immediate effects of impact
- Immense earthquakes >11 magnitude
- Widespread tsunami
- Worldwide ejecta (thick curtain in many places)
- Combo of asteroid material, melted rocks, and hot air
- Worldwide pulse of intense thermal energy
find more resources at oneclass.com
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Document Summary
1980 walter and luis alvarez (ucb) proposed that 10km diameter asteroid struck the earth causing the mass extinction. Still, as late as 1988, more than half of all american paleontologists contacted in a survey continued to believe that the extinction of the dinosaurs was in no way related to an impact. Uniformitarianism (look at processes occurring today, use simple gradual processes to explain big things on earth) and catastrophism: the smoking gun (1991) Chicxulub crater, mexico ~ 200-300km diameter crater dated to 66ma. Today, crater buried under >1km of cenozoic sedimentary rock. Complicated discovery history (1st evidence was geophysical data from all researchers) but lots of shocked quartz and presence of k-pg boundary was the clincher (reported in 1991) Even after chicxulub crater is found in 1991 many scientists still doubt that it would be devastating enough to cause a mass extinction. Impact began on july 16 1994 and lasted for a week.
