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Catastrophes and Prehistory


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Author Topic: Catastrophes and Prehistory  (Read 6321 times)
Troy Exeter
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« Reply #15 on: March 18, 2007, 10:20:23 pm »

Asteroid/Comet Impact Craters and Mass Extinctions
and Shiva Hypothesis of Periodic Mass Extinctions.
 
by Michael Paine


[Craters by age] [Volcano and climate change links] [Updates] [Chicxulub debate][More on extinctions] [Falklands] [Impacts and vulcanism] [Shiva Hypothesis - periodic extinctions]

Craters by age
Since writing my Space.com/Explorezone article  "How an asteroid impact causes extinction" in 1999, I have gathered some  more information about the possible links between asteroid impacts and mass extinctions. There also appears to be a link between large impacts and volcanic eruptions.
The following graph shows impact craters on Earth by age and diameter. Also shown are the main geologic boundaries involving mass extinctions (tall, bold lines), minor boundaries (thin, short lines - fewer extinctions) and the approximate timing of "flood basalt eruptions". Originally the graph only showed craters which aligned with major extinction events but it was considered better to show all craters 20km diameter or more to avoid "counting the hits and ignoring the misses". Those which appear to align with a geologic boundary are shown as dark blue diamonds. The most notable is Chicxulub at the Cretaceous/Tertiary boundary - the event that saw the extinction of the dinosaurs.

Since multiple impacts appear to be very common throughout the solar system it is expected that some of the smaller craters are associated with other major impacts, evidence of which has not been discovered or has vanished over time. For example, the Triassic/Jurassic and Jurassic/Cretaceous boundaries appear to involve multiple impacts. Craters 40km diameter or more are likely to be caused by 2km diameter asteorids or comets. Such impacts would probably result in severe global climate disruption but it takes an asteroid/comet 10km or larger to cause mass extinctions. It is estimated that such impacts occur, on average, once every 50 to 100 million years.



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