A report today in the Journal Science (subscription required) argues that comet or metorite impacts may have lead to the demise of the wolly mammoth as well as early human settlers in North America. You can read a BBC article on the research here.
It's pretty widely accepted that impacts can cause mass extinctions. The most famous example is the dinosaurs about 65 million years ago. We have found multiple lines of evidence that an impact caused this extinction including iridium and other unusual elements in sedimentary rocks from this time period and the impact crater off the coast of the Yucatan peninsula (I am not going to try and spell the name of the crater!)
The impact in question would have occurred about 12,900 years ago. They have found iridium in rock layers (called the Younger Dryas or YD Boundary) as well as evidence of large wildfires that can be started by large impacts. They also found nanodiamonds at various sites around North America. Nanodiamonds don't form naturally on Earth's surface, but can form in impacts (if you want go get really technical, they found both cubic diamonds and what are called n-diamonds which have unusal indicies of refraction. n-diamonds are known to occur in metorites but not form naturally on Earth's surface).
But what about the crater? One idea is that the impactor never hit the ground but instead gave rise to an air burst. This would not produce a crater. The Tunguska impact in 1908 was an airburs and leveled quite a large area of forest in Siberia.
This would be an exciting discovery if they could prove an impactor caused this extinction. The more we learn about impacts, their frequency and effects on Earth, the better prepared we will be to handle potential future events.
Reprinted with permission from the Half-Astrophysicist Blog.
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5 comments:
I recently saw on TV where a meteorite hit earth in the Cancun area (a LARGE one) at the same time a volcano erupted in Sibera which could have each demolished vegatation around 1/2 the earth. There was a theory that if a major occurance happened at one point it would cause an occurance at the opposite point. Pretty deep thinking here.
A new theory-I was under the impression that the the combined forces of climate change and mankind led to the extinction of many prehistoric mammals. But this is regional(North America). I wonder what impact did this metorite have globally.
I haven't heard that one anon...if you can cite a source, I would be interested to see it. I have seen some stuff on nearby volcanoes erupting near the same time, possibly due to seismic influences. Haven't heard of any that far apart being linked, but not going to rule it out either.
Yes, drew. They do discuss the possibilities of over hunting and climate change leading to the extinctions as well, but argue that the climate change was too slow to cause the extinctions. Piecing together what happened ~13,000 years ago can be tricky.
How large does an object have to be in order to be detected far enough in advance to do something about it? According to this source (via Wikipedia), a meteor "50-100 meters in diameter" caused the Tunguska event. That wasn't climate changing.
Well, orbs, there has only been ONE meteor that was detected before it hit and that was just this fall. It did an airburst over Sudan and was about 2 meters (7 feet roughly) across. We only saw it about one day before it hit, so didn't have much warning (good thing it was small).
So we can pretty much detect anything that would be a threat in terms of size...it's just a matter of getting some really wide field telescopes built that can scan the whole sky often enough to find these things!
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