Re: [新聞] 奈米金剛鑽 長毛象滅絕證據
看板EarthScience作者ALPHONSE2501 (ALPHONSE2501)時間17年前 (2009/01/07 04:19)推噓0(0推 0噓 0→)留言0則, 0人參與討論串2/2 (看更多)
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: ※ [本文轉錄自 sky 看板]
: 發信人: SSR2000.bbs@bbs.cs.nctu.edu.tw (在家大修中), 看板: sky
: 標 題: [新聞] 奈米金剛鑽 長毛象滅絕證據
: http://udn.com/NEWS/WORLD/WOR3/4670501.shtml
: 【聯合報╱編譯林沿瑜╱報導】
: 2009.01.03 03:08 am
: 科學家相信，6500萬年前恐龍因為彗星撞地球造成的大火，以及濃霧遮天的
: 氣溫驟降而滅絕。
: 2日出刊的美國「科學」（Science）期刊更進一步指出，1萬2900年前消
: 失的長毛象和乳齒象也是因為彗星撞地球而絕種，而關鍵證據就是數十億
: 顆肉眼無法看見的「奈米金剛鑽」。
: 科學家認為，1萬2900年前，一顆直徑約4000公尺的慧星撞擊了現今北美
: 大陸，導致地殼變動，大火、洪水四處蔓延，草原、森林燃燒殆盡，天空
: 出現了濃濃的黑色霧團。
: 此時，北美東北部勞倫泰德冰河的部分地區開始融化，融化後的河水則向
: 南流到了現在的密西西比州、進入墨西哥灣，這又進一步引起了大西洋洋
: 流的變化。
: 地球環境的急遽變化揭開了此後1300年的「新仙女木」冰河期（Younger
: Dryas），當時有多達35種哺乳類動物不是立即消失，就是因為數目驟減
: ，而在人類獵捕後滅絕，其中包括長毛象、乳齒象、美洲駱駝、短面熊、
: 巨水獺、恐狼、古美洲獅。
: 除了哺乳類動物之外，當時建立克洛維斯（Clovis）文化的古印地安土著
: 人數大減，其建立的文化也因此中斷。
: 其實，發表這篇論文的奧勒岡大學教授肯尼特早在去年就表示，他們已經
: 在北美洲的10個考古地點發現了「黑土層」，而且利用「碳14年代測定法
: 」得知形成於1萬2900年前。
: 由於「黑色層」中含有地球少見的銥元素、碳粒子，以及含有氦-3的富勒
: 烯（Fullerene），凡此都呈現出受到外太空影響的特徵。
: 不過更令科學家振奮的是，他們又在「黑土層」的底部發現了數十億顆連
: 電子顯微鏡都很難看到的「奈米金剛鑽」。
: 因為「奈米金剛鑽」只在極高溫、高壓的環境下形成，更加證實了「新仙
: 女木」冰河期與彗星撞地球的關連性。
: 另外，「奈米金剛鑽」也曾在區隔恐龍世代的土壤層中被發現，顯示恐龍
: 滅絕與長毛象絕跡都受到外太空隕石撞擊地球的影響。
: 【2009/01/03 聯合報】
http://www.latimes.com/news/science/la-sci-extinction2-2009jan02,0,896970.story
Diamonds show comet struck North America, scientists say
The impact caused an ice age that killed some mammal species and many humans
12,900 years ago, researchers report. They say the discovery of tiny
heat-formed diamonds is proof of the catastrophe.
By Thomas H. Maugh II
January 2, 2009
A discovery of microscopic diamonds a few feet beneath the surface of North
America reveals that a comet caused a cataclysm of fire, flood and
devastation nearly 13,000 years ago that extinguished mammoths and mastodons
and dealt a blow to early civilization, scientists said Friday.
The nanodiamonds, so small that they are barely visible in an electron
microscope, are thought to be remnants of that comet, which would have hit
about 65 million years after the much larger collision that wiped out the
dinosaurs.
According to the theory -- which has its critics -- as the comet broke apart,
it rained fire over the entire continent, igniting the plains and the forests
and creating choking clouds of smoke.
Heat from the explosions and the massive fires melted substantial portions of
the Laurentide glacier in Canada, sending waves of water down the Mississippi
and into the Gulf of Mexico. That triggered changes in Atlantic Ocean
currents, which ushered in a 1,300-year ice age known as the Younger Dryas.
Battered by fire and ice, as many as 35 species of mammals, including
American camels, the short-faced bear, the giant beaver, the dire wolf and
the American lion, either immediately vanished or were so depleted in number
that humans hunted them to extinction.
The humans, a Paleo-Indian grouping known as the Clovis culture for the
distinctive spear points they employed, suffered a major population drop,
disappearing in many areas for hundreds of years.
The researchers -- including James P. Kennett of UC Santa Barbara and Douglas
J. Kennett of the University of Oregon -- had earlier discovered the thin
layer of black soil containing iridium and other debris that they thought
indicated a massive comet or meteor impact. But critics suggested a variety
of less dire explanations.
The discovery of the nanodiamonds, however, reported Friday in the journal
Science, provides the most powerful support for the comet theory because the
gems can only be created under the extreme temperatures and pressures of a
massive explosion, such as a comet striking the Earth's surface.
"There's no other way we can interpret the presence of these diamonds other
than an extraterrestrial impact," said James Kennett, a paleooceanographer.
Such an impact would be the most likely source of nanodiamonds, critics
agreed. But many argued that the one-page paper in Science did not provide
enough evidence to support the authors' claim.
"Nanodiamonds could be a good indicator of an impact event . . . but after
reading the paper, I wasn't convinced they found diamonds," said physicist
Tyrone Daulton of Washington University in St. Louis. "Maybe they found
diamonds and maybe they didn't."
Spectroscopist Peter Buseck of Arizona State University said that he
"wouldn't question that they saw nanodiamonds," but added that for such a
potentially important discovery, he "would like to have it well supported."
Archaeologist Douglas Kennett, lead author of the report and James Kennett's
son, conceded that the restrictive format of the rapid publication limited
the amount of data the team could incorporate into their paper.
But he said the presence of nanodiamonds had been confirmed in three separate
laboratories. "There are going to be a lot of follow-up papers that will
clearly demonstrate that these are diamonds," he said.
The findings may tie together a variety of hitherto mysterious events in
North America that all occurred beginning about 12,900 years ago, the
beginning of the Younger Dryas -- also known as the Big Freeze.
The Kennetts and their colleagues reported last year that they had found the
black layer, radiocarbon-dated to 12,900 years ago, at 10 archaeological
sites scattered around the continent.
In addition to charred remains from forests and other flora, the black mat
contains iridium, carbon spherules and fullerenes containing helium-3, all
characteristic of an extraterrestrial impact.
But critics said the evidence was insufficient to prove an impact,
particularly in the absence of a demonstrable crater.
James Kennett and his colleagues went back to the mats they had collected and
performed what he termed the "extremely labor-intensive" process of looking
for the nanodiamonds. That involved using acids to dissolve everything else
in the samples, then using a variety of techniques to identify the diamond
residue.
They found a family of at least five different forms of diamonds, including
some that are formed only by impacts, they reported in the Science paper.
Moreover, the nanodiamonds were found only at the bottom of the black mat --
not in the soil either below or above it.
Such diamonds have previously been found in the thin layer of soil that marks
the boundary between the Cretaceous and Tertiary eras of Earth's history 65
million years ago, when the dinosaurs disappeared in the aftermath of what is
widely believed to have been a meteorite impact.
In a series of papers presented last month at a meeting of the American
Geophysical Union in San Francisco, the team also reported that at least 15
of the 35 species that became extinct during the Younger Dryas disappeared
within 100 years of the event.
Their fossils appear "right up to the base of the black mat and never go
above it," James Kennett said.
The other species may have been hunted to extinction by humans, as has often
been speculated, but only after their numbers were greatly reduced by the
fires and climate change.
There was also a "major population crash" of humans, he added: In the Great
Plains, all traces of humans disappeared for about 200 years. Southern
California was even more severely affected, with evidence of human occupation
disappearing for most of the Younger Dryas.
James Kennett is convinced there was a cometary impact.
"I've counted up 15 major things that occurred at 12,900 years ago," he said.
"I'd like somebody to explain that to me in some other way."
thomas.maugh@latimes.com
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