Seattle - Nov 6, 2001
Even such mythical detectives as Sherlock Holmes or Hercule Poirot would have difficulty trying to find the culprit that killed the mammoths, mastodons and other megafauna that once roamed North America.
Scientists have been picking over the bones and evidence for more than three decades but cannot agree on what caused the extinction of many of the continent's large mammals.
Now, in two new papers, a University of Washington archaeologist disputes the so-called overkill hypothesis that pins the crime on the New World's first humans, calling it a "faith-based credo" that bows to Green politics.
"While the initial presentation of the overkill hypothesis was good and productive science, it has now become something more akin to a faith-based policy statement than to a scientific statement about the past," said Donald Grayson, a UW anthropology professor.
Writing in the current issue of the Journal of World Prehistory and in a paper to be published in a forthcoming issue of the Bulletin of the Florida Museum of Natural History, Grayson said there are dangerous environmental implications of using overkill hypothesis as the basis for introducing exotic mammals into arid western North America."
He looks askance at the idea of introducing modern elephants, camels and other large herbivores into the southwest United States.
"Overkill proponents have argued that these animals would still be around if people hadn't killed them and that ecological niches still exist for them. Those niches do not exist. Otherwise the herbivores would still be there."
If early humans didn't kill North America's megafauna, then what did?
Grayson points to climate shifts, during the late Pleistocene epoch, which ended about 10,000 years ago, and subsequent changes in weather and plants as the likely culprits in the demise of North America's megafauna.
The massive ice sheets that covered much of the Northern Hemisphere began retreating. In North America, this icy mantle prevented Arctic weather systems from extending into the mid-continent.
Seasonal weather swings were less dramatic and didn't reach as far south as they presently do. But with this change, the climate became more similar to today's, marked by cold winters and warm summers.
As a result, an unusual patchwork aggregation of plant communities ceased to exit and there was a massive reorganization of biotic communities. At the same time, new data developed by Russell Graham, a paleontologist with the Denver Museum, shows that small mammals such as shrews and voles were moving about the landscape and becoming locally extinct. And there were the extinctions of some 35 genera of large North American mammals, including horses, camels, bears, giant sloths, saber-toothed cats, mastodons and mammoths.
The overkill hypothesis was proposed by retired University of Arizona ecologist Paul Martin in 1967 and its basic arguments haven't changed since. It claims:
First of all there is no compelling evidence that the majority of the extinctions occurred during Clovis times, said Grayson. Only 15 genera can be shown to have survived beyond 12,000 years ago and into Clovis times.
For 30 years, overkill proponents have assumed that since some genera can be shown to have become extinct around 11,000 years ago, all the big North American mammals became extinct at that time, he said.
"That's an enormous assumption, even though there is no compelling evidence of it in North America," Grayson said.
He also said overkill proponents have consistently ignored the possibility that the Clovis people were not the first humans in the New World. They reject evidence from a site in Monte Verde, Chile, showing human occupation that dates some 12,500 to 12,800 years ago. Monte Verde also has yielded some material that may push human occupation back to 33,000 years before the present.
Well-accepted Clovis sites dating between 10,800 and 11,300 years ago have been found in North America, and distinctive, fluted projectile points mark this culture. Clovis artifacts have been found with mammoth remains in more than a dozen sites across the Great Plains and the southwestern United States.
Grayson said there is no reason to doubt that these people scavenged and hunted large mammals. But he cautioned that while mammoths, mastodons, horses and camels were the most common large mammals in the late Pleistocene -- 10,000 to 20,000 years ago -- only mammoths are found at kill sites associated with Clovis people.
As for the claim that human colonization of the world's islands resulted in widespread vertebrate extinction, Grayson said this did not occur simply because of human hunting.
"No one has ever securely documented the prehistoric extinction of any vertebrate as a result human predation, though it may certainly have happened. In virtually all cases, when people colonize an area many other changes follow -- fire, erosion and the introduction of a wide range of predators and competitors.
"We do know that human colonists caused extinctions in isolated, tightly bound island settings, but islands are fundamentally different from continents," he added.
"The overkill hypothesis attempts to compare the incomparable and there is no evidence of human-caused environmental change in North America. But there is evidence of climate change. Overkill is bad science because it is immune to the empirical record."
University of Washington
Subscribe To SpaceDaily Express
Search For Martian Life Will Need Good Vibrations
Bradford - Oct 10, 2001
University of Bradford PhD student Emma Newton is playing a part in helping NASA's future exploration of Mars which many people hope will lead to discovering life on the planet.
Researchers Find Glass-Eating Microbes at the Rock Bottom on Food Chain
San Diego - Oct 9, 2001
Welcome to the bottom of the deep-sea food chain. The rock bottom, that is. In the current edition of Geochemistry, Geophysics, Geosystems, a team of researchers uncovers and characterizes a process that is commonplace below the ocean bottom. In the upper 300 meters of the earth's oceanic crust, microbes were found to have literally eaten their way through rock.
Scientists Toast the Discovery of Vinyl Alcohol in Interstellar Space
Kitt Peak - October 1, 2001
Astronomers using the National Science Foundation's 12 Meter Telescope at Kitt Peak, AZ, have discovered the complex organic molecule vinyl alcohol in an interstellar cloud of dust and gas near the center of the Milky Way Galaxy. The discovery of this long-sought compound could reveal tantalizing clues to the mysterious origin of complex organic molecules in space.
Bacterial Communities Found to Follow Water - Implications for Mars?
Tempe - Sept. 26, 2001
Miraculous things happen to the desert when it rains - everything changes from brown to green and organisms that have not been seen for months make a brief emergence from underground lairs.
Why Microbes Matter
Houston - Sept. 4, 2001
One of the most frequent questions that I have encountered when talking with people about astrobiology is, "If there are microorganisms on Mars, so what? Why should I be interested in the Martian equivalent of bacteria?" Here is my answer:
Permian Impact Caused Largest Mass Extinction on Earth
Boulder - August 27 2001
What actually ended the Permian Period some 251 million years ago? Most Earth scientists think gradual sea fall, climate change, oceanic anoxia, and volcanism were the causes. But that's not so. A group of geologists working in southern China found evidence that it was an asteroid or a comet that smacked our planet, exploded, and then caused the most severe biotic crisis in the history of life on Earth.
Advancing Our Understanding of Life
Washington - Aug 21, 2001
Over the past two decades, advances in a number of scientific disciplines have helped us better understand the nature and evolution of life on Earth. These scientific developments also have helped lay the foundation for astrobiology, opening up new possibilities for the existence of life in the Solar System and beyond.
|The content herein, unless otherwise known to be public domain, are Copyright 1995-2016 - Space Media Network. All websites are published in Australia and are solely subject to Australian law and governed by Fair Use principals for news reporting and research purposes. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA news reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. Advertising does not imply endorsement, agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement All images and articles appearing on Space Media Network have been edited or digitally altered in some way. Any requests to remove copyright material will be acted upon in a timely and appropriate manner. Any attempt to extort money from Space Media Network will be ignored and reported to Australian Law Enforcement Agencies as a potential case of financial fraud involving the use of a telephonic carriage device or postal service.|