wade davis, anthropologist, speaks of the varied world of ethnodiversity and how varied culture is so important to the human race.
Sunday, July 24, 2011
Thursday, July 21, 2011
THE LAST EXTINCTION
in 11,900 bc (now called. "bce" for "before common era") the large beasts of north america became extinct and no knows for certain why they suddenly became extinct. these large beasts included several species of wooly mammoth, the mastodon, the giant sloth, the saber-tooth cat ("saber-tooth tiger"), the glyptodon, (a giant version of today's armadillo), as well as others. also, why is it that some animal species survived and others did not? time, in the geological sense, is measured in layers of dirt, lake mud and ice. every year the earth deposits dust and snow upon its surface. dirt layers can be measured for millions of years and ice to about 400,000 years, as ice did not exist on earth for its entire 4.5 billion year history. going "back in time" in the geological record, to the time of the extinction of these large beasts, 11,900 bce, a layer known as the "black matt" is visible. this "black matt" is a layer of soil quite different from the layers above and below it, previous in time and beyond it in time. the soil is black and contains different elements than other layers and holds some of the evidence necessary to explain this extinction.
the theories:
early humans crossed the land bridge in 15,000 bce and hunted the large beasts into extinction, but the amount of early humans in north america at the time and the ability to systematically hunt and eliminate every last beast is highly unlikely with the technology available at the time and not plausible at all.
or was it just climate change, from some unknown reason, that warmed the earth, ending the last ice age and creating an environment unsuitable for large beasts? there is evidence of previous climate change, but these large beasts survived it, so why did they not survive this past change in 11,900 bce? could early human hunter-gatherers combined with climate change have been the cause?
or could it have been a large scale extraterrestrial object, such as a comet or an asteroid impacting earth, causing large amounts of atmospheric dust, longer winters and disrupting the global food supply, making it most difficult for large beasts to survive? this scenario is similar to the extinction of the dinosaurs, but is there sufficient evidence to support this? where is the impact crater? if there was no ground impact, an atmospheric explosion of a comet or asteroid is possible, but would have generated large surface plasma fires, destroying vast amounts of plant life, and changing the landscape into something quite different than what we have today.
there are even more possible scenarios that could have taken place as well, but all with devastating effects to all life, not just to large beasts.
the evidence, amassed so far:
evidence in this "black matt" geological layer points to astronomical causes, like the discovery of iridium, found only in rare amounts on earth, but replete in space objects, such as asteroids and comets.
evidence in the greenland ice sheet, the geological record for earth, as well as evidenced in the "black matt" layer, shows hex-shaped nanoscale diamonds, not the typical earth-bound cubic-shaped nanoscale diamonds. these hex-shaped nanoscale diamonds are quite common in asteroids and comets and are extremely rare as naturally occurring on earth.
these, and other discoveries, currently point to the conclusion that an asteroid or a comet impacted the earth at the time of the "black matt" extinction, in 11,900 bce. so where is the impact crater? if a large extraterrestrial object hit the earth's crust in such recent history, the impact crater would be almost perfectly preserved, as erosion and geological intervention can take millions of years to obscure the original shape and structure of such an impact crater. there is no such impact crater in north america. maybe this extraterrestrial object did not impact land directly. if such an object exploded into fragments in mid atmosphere, and then impacted the surface of the earth, it would have created small impact craters, which could have easily been erased over the last 13,000 years due to erosion and the like. or if such an object hit the ice sheet of the last ice age, or, more likely, split into fragments in mid atmosphere before impacting the ice sheet, there would be no impact crater, and this would account for the iridium and the hex-shaped nanoscale diamonds.
there are still unanswered question surrounding this hypothesis, for instance, why was a frozen mammoth discovered recently in antarctica found with undigested daisies in it's stomach (suggesting an almost instant freezing of the creature)?
the comet fragment impact is the best guess so far, and will be the current accepted explanation for the extinction of the large prehistoric beasts until future discovered evidence proves otherwise.
the theories:
early humans crossed the land bridge in 15,000 bce and hunted the large beasts into extinction, but the amount of early humans in north america at the time and the ability to systematically hunt and eliminate every last beast is highly unlikely with the technology available at the time and not plausible at all.
or was it just climate change, from some unknown reason, that warmed the earth, ending the last ice age and creating an environment unsuitable for large beasts? there is evidence of previous climate change, but these large beasts survived it, so why did they not survive this past change in 11,900 bce? could early human hunter-gatherers combined with climate change have been the cause?
or could it have been a large scale extraterrestrial object, such as a comet or an asteroid impacting earth, causing large amounts of atmospheric dust, longer winters and disrupting the global food supply, making it most difficult for large beasts to survive? this scenario is similar to the extinction of the dinosaurs, but is there sufficient evidence to support this? where is the impact crater? if there was no ground impact, an atmospheric explosion of a comet or asteroid is possible, but would have generated large surface plasma fires, destroying vast amounts of plant life, and changing the landscape into something quite different than what we have today.
there are even more possible scenarios that could have taken place as well, but all with devastating effects to all life, not just to large beasts.
the evidence, amassed so far:
evidence in this "black matt" geological layer points to astronomical causes, like the discovery of iridium, found only in rare amounts on earth, but replete in space objects, such as asteroids and comets.
evidence in the greenland ice sheet, the geological record for earth, as well as evidenced in the "black matt" layer, shows hex-shaped nanoscale diamonds, not the typical earth-bound cubic-shaped nanoscale diamonds. these hex-shaped nanoscale diamonds are quite common in asteroids and comets and are extremely rare as naturally occurring on earth.
these, and other discoveries, currently point to the conclusion that an asteroid or a comet impacted the earth at the time of the "black matt" extinction, in 11,900 bce. so where is the impact crater? if a large extraterrestrial object hit the earth's crust in such recent history, the impact crater would be almost perfectly preserved, as erosion and geological intervention can take millions of years to obscure the original shape and structure of such an impact crater. there is no such impact crater in north america. maybe this extraterrestrial object did not impact land directly. if such an object exploded into fragments in mid atmosphere, and then impacted the surface of the earth, it would have created small impact craters, which could have easily been erased over the last 13,000 years due to erosion and the like. or if such an object hit the ice sheet of the last ice age, or, more likely, split into fragments in mid atmosphere before impacting the ice sheet, there would be no impact crater, and this would account for the iridium and the hex-shaped nanoscale diamonds.
there are still unanswered question surrounding this hypothesis, for instance, why was a frozen mammoth discovered recently in antarctica found with undigested daisies in it's stomach (suggesting an almost instant freezing of the creature)?
the comet fragment impact is the best guess so far, and will be the current accepted explanation for the extinction of the large prehistoric beasts until future discovered evidence proves otherwise.
Subscribe to:
Posts (Atom)