My OperaWho or What was the North American Mammoth-Killer ?
Tuesday, November 24, 2009 3:46:17 PM
Did an exploding comet wreak havoc on man and beast 13,000 years ago across North America. This question was much debated a year or two ago (including one of my posts). The conclusion of a new study published in the latest issue of Science is - NO !
As the blog cryology and co. nicely puts it in a post titled “Extinctions & Excrements” the study used ‘an unusual data source - fossil excrements and the inhabitants of this "biotope"’.
Twenty thousand years ago, North America had a very impressive range of big mammals. By 10,000 years ago, 34 genera of these mammals were gone, including the 10 species that weighed more than a ton. Many other drastic changes occurred in this interval, all of which have been advocated as possible causes of megafaunal extinction. The climate flipped from cold to warm, then back to cold in a 1000-year chill (the Younger Dryas), before rapidly rewarming. There were more, larger fires, and the structure and species composition of vegetation changed drastically. People arrived, and the Clovis culture—with a characteristic style of beautifully crafted stone spear points—flourished for less than 1000 years.
The new study used a tiny organism to reconstruct the decline of the very biggest animals. Sporormiella is a fungus that produces spores in the dung of large plant eating animals. Lots of dung means lots of spores, so Sporormiella gives an index of the biomass of large plant eaters. The spores accumulate in sediments along with pollen and charcoal, allowing changes in biomass of large plant eaters to be matched exactly to sediment records of vegetation and fire, which can in turn be dated and aligned with other archaeological and environmental records.
The authors found that the decline of the big animals began around 14,800 years ago and took more than a thousand years. Large vegetation changes and an increase in fire followed this decline. It is important to notice that all this happened long before the proposed extraterrestrial impact. Climate change as a cause also looks implausible: Climate would most likely have affected the big animals by changing vegetation, but vegetation changes followed the animal decline. The animal decline began more than a thousand years before the Clovis period, so we cannot blame them either. Earlier human communities may, however, have been responsible for the initial decline.
Before 14,800 years ago, the environment around the site studied by Gill et al. was an open savanna or parkland, probably with scattered spruce and rare broad-leaved trees growing over a short grass-dominated pasture, and almost no fire. As the megafauna declined, woody biomass increased, mainly by growth of broad-leaved trees that had presumably been suppressed by the large plant eating animals. The result was a transitory spruce/broadleaf woodland, the like of which does not exist today. Big fires broke out around 14,000 years ago, and for the next few thousand years, major fires returned every few centuries. These changes were widespread. Fire increased throughout North America around 14,000 years ago.
The study seems to rule out several hypothesized causes and effects of the megafaunal extinction but does not conclusively resolve the debate over climatic versus human causation (or both) of the North American megafaunal extinctions.
Reference:
Pleistocene Megafaunal Collapse, Novel Plant Communities, and Enhanced Fire Regimes in North America
By Gill et al.
Science 20 November 2009:
Vol. 326. no. 5956, pp. 1100 - 1103
DOI: 10.1126/science.1179504
As the blog cryology and co. nicely puts it in a post titled “Extinctions & Excrements” the study used ‘an unusual data source - fossil excrements and the inhabitants of this "biotope"’.
Twenty thousand years ago, North America had a very impressive range of big mammals. By 10,000 years ago, 34 genera of these mammals were gone, including the 10 species that weighed more than a ton. Many other drastic changes occurred in this interval, all of which have been advocated as possible causes of megafaunal extinction. The climate flipped from cold to warm, then back to cold in a 1000-year chill (the Younger Dryas), before rapidly rewarming. There were more, larger fires, and the structure and species composition of vegetation changed drastically. People arrived, and the Clovis culture—with a characteristic style of beautifully crafted stone spear points—flourished for less than 1000 years.
The new study used a tiny organism to reconstruct the decline of the very biggest animals. Sporormiella is a fungus that produces spores in the dung of large plant eating animals. Lots of dung means lots of spores, so Sporormiella gives an index of the biomass of large plant eaters. The spores accumulate in sediments along with pollen and charcoal, allowing changes in biomass of large plant eaters to be matched exactly to sediment records of vegetation and fire, which can in turn be dated and aligned with other archaeological and environmental records.
The authors found that the decline of the big animals began around 14,800 years ago and took more than a thousand years. Large vegetation changes and an increase in fire followed this decline. It is important to notice that all this happened long before the proposed extraterrestrial impact. Climate change as a cause also looks implausible: Climate would most likely have affected the big animals by changing vegetation, but vegetation changes followed the animal decline. The animal decline began more than a thousand years before the Clovis period, so we cannot blame them either. Earlier human communities may, however, have been responsible for the initial decline.
Before 14,800 years ago, the environment around the site studied by Gill et al. was an open savanna or parkland, probably with scattered spruce and rare broad-leaved trees growing over a short grass-dominated pasture, and almost no fire. As the megafauna declined, woody biomass increased, mainly by growth of broad-leaved trees that had presumably been suppressed by the large plant eating animals. The result was a transitory spruce/broadleaf woodland, the like of which does not exist today. Big fires broke out around 14,000 years ago, and for the next few thousand years, major fires returned every few centuries. These changes were widespread. Fire increased throughout North America around 14,000 years ago.
The study seems to rule out several hypothesized causes and effects of the megafaunal extinction but does not conclusively resolve the debate over climatic versus human causation (or both) of the North American megafaunal extinctions.
Reference:
Pleistocene Megafaunal Collapse, Novel Plant Communities, and Enhanced Fire Regimes in North America
By Gill et al.
Science 20 November 2009:
Vol. 326. no. 5956, pp. 1100 - 1103
DOI: 10.1126/science.1179504
- http://www.sciencemag.org/cgi/content/short/326/5956/1072
- http://www.sciencemag.org/cgi/content/abstract/sci;326/5956/1100
- http://rockglacier.blogspot.com/2009/11/extinctions-excrements.html
- http://my.opera.com/nielsol/blog/2007/06/11/belgium-iridum-and-clovis
- http://www.huliq.com/22756/researchers-involved-in-new-clovis-age-impact-theory
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