If you've been keeping up, you've no doubt noticed that the debate over what led to the extinction of the North American megafauna some 13,000 years ago is almost as heated as teh debate over what became of the dinosaurs 65 million years earlier. Another entry....What we know is that shortly after the end of the last ice age, the glaciers that covered much of North America began to melt and retreat toward the pole. However, a sudden cooling period known to geologists as the Younger Dryas reverse the retreat for a period of over 1,000 years. During that time, something dramatic happened to the great mammals of North America - the mammoths and mastodons, the sloths and sabertooths, almost all of them, vanished. What we don't know is - why?
The prevailing hypothesis for some time has been that of human hunting overkill - the idea that sophisticated hunters of the developing Clovis culture took advantage of a naive fauna and hunted them to extinction. This is supported by the many Clovis sites that have been uncovered that provide evidence of hunting activity. One of the best studied is the Murray Springs site in southeastern Arizona, where a Clovis hunting camp is in close proximity to a mammoth and bison kill. The overkill hypothesis has been challenged recently by a group claiming that evidence points toward an extraterrestrial impact (that's a comet or an asteroid, not a spaceship), with the resultant climatic changes that entails. This, of course, is similar to the impact theory that currently holds sway regarding the disappearance of the dinosaurs at the K-Pg boundary 65.5 million years ago.
In a new paper appearing in the Proceedings of the National Academy of Sciences, a group from the University of Arizona takes a look at the evidence suggested to support the extraterrestrial impact theory. That evidence takes three main forms: spherical magnetic particles (thought to be formed by impacts) found in soil at the Murray Springs site, high concentrations of iridium (a component of asteroids) in soils dating to the time of the extinctions, and high charcoal content (an indication of the fires that would have resulted from an impact). The group concludes that there is nothing in these three lines of evidence that cannot be explained by terrestrial answers. In other words, they can't rule out an asteroid impact, but the evidence doesn't require one. I suppose this leaves the overhunting hypothesis as the default explanation.
It's worth mentioning the the man most associated with notion of a Clovis megafaunal wipeout is Paul Martin, who first proposed the possibility of Pleistocene overkill in the 1960s and has published extensively on the topic. Paul Martin is now professor emeritus at - the University of Arizona.
Excellent summary here at Science Daily.
In a new paper appearing in the Proceedings of the National Academy of Sciences, a group from the University of Arizona takes a look at the evidence suggested to support the extraterrestrial impact theory. That evidence takes three main forms: spherical magnetic particles (thought to be formed by impacts) found in soil at the Murray Springs site, high concentrations of iridium (a component of asteroids) in soils dating to the time of the extinctions, and high charcoal content (an indication of the fires that would have resulted from an impact). The group concludes that there is nothing in these three lines of evidence that cannot be explained by terrestrial answers. In other words, they can't rule out an asteroid impact, but the evidence doesn't require one. I suppose this leaves the overhunting hypothesis as the default explanation.
It's worth mentioning the the man most associated with notion of a Clovis megafaunal wipeout is Paul Martin, who first proposed the possibility of Pleistocene overkill in the 1960s and has published extensively on the topic. Paul Martin is now professor emeritus at - the University of Arizona.
Excellent summary here at Science Daily.
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