79万年前的多次天体撞击
资料来源——德国海德堡大学主页
翻译——中国陨石网青藏大卫
欢迎转载，转载请注明中国陨石网
资料发表时间2016年2月22日
海德堡的研究人员确定了来自世界各地的玻璃岩石的年龄。
大约79万年前，发生了多次天体撞击地球的全球性事件。通过对来自世界各地的所谓的冲击玻璃（tektites）测年后，来自海德堡大学的地球科学家得出了这个结论。马里奥特里洛夫博士兼教授指导下的研究小组，研究了几种在小行星或彗星撞击下产生的岩石玻璃。海德堡的科学家们采用了一种基于自然发生的同位素的测年方法，使他们能够比以往更准确地测定岩石的年龄。他们的研究表明，来自亚洲，澳大利亚，加拿大和中美洲的样品在年龄上几乎相同，尽管在某些情况下它们的化学性质明显不同。这说明不同的冲击事件一定发生在同一时间。他们的研究得到了Klaus Tschira基金会资助，研究成果发表在《地球化学和天体化学杂志》上。
地球科学研究所和Klaus Tschira宇宙化学实验室的研究小组利用同位素测量来确定由外星岩石撞击引起的陨石坑的年龄。马里奥特里洛夫说：“这就是我们如何知道陨星何时、何地、如何频繁的撞击地球，以及它们有多大”。据特里洛夫教授称，很久以来有迹象表明一次主要的这种类型事件发生在大约一百万年前的地球上。这可以从冲击玻璃中得到证实，这种岩石玻璃在冲击过程中产生，地球物质会融化，被冲击到数百公里之外，然后变硬成为玻璃。
这项研究的主要作者温弗里德-施瓦茨博士解释说：“我们从澳大拉西亚地区已经知道这种冲击玻璃有一段时间了”。这些岩石玻璃形成了从印度支那延伸到澳大利亚最南端的散落地。更小的冲击玻璃，被称为微型冲击玻璃，在马达加斯加海岸和南极洲内部的钻孔岩芯中也被发现。这块岩石玻璃已经散落了一万多公里，其中一些甚至离开了地球的大气层。 使用40Ar-39Ar测年方法，分析自然产生的40K同位素的衰变，海德堡研究人员成功地比以前更准确地测定了这些岩石的年龄。
“我们的数据分析表明，大约79.3万年前一定有一次天体撞击事件，持续了8,000年的时间，”温弗里德-施瓦茨解释道。 海德堡的科学家也研究了来自加拿大和中美洲的样本。 加拿大的岩石玻璃具有与澳大拉西亚冲击玻璃相同的化学成分和年龄，并且可能与南澳大利亚或南极发现的样品具有类似的“飞行路线”。 根据施瓦茨博士的说法，其他发现必须首先确认，样品回收地点确实是样品原始着陆的地方，或者例如是被人携带过去的。
来自中美洲的岩石玻璃也是冲击玻璃 - 第一批标本是在玛雅人的礼拜场所发现的。 同样的，中美洲又有了其它的数百个发现。 “这些岩石的化学成分明显不同，它们的地理分布也表明它们来自不同的冲击事件，”施瓦茨博士解释说。 “令人惊讶的是，我们的年龄估计证明它们起源于77.7万年前，偏离了16,000年。 在误差范围内，这与澳大拉西亚的冲击玻璃的年龄相匹配。“
这些发现导致海德堡研究人员得出结论，大约79万年前有多次天体撞击事件。 除了澳大拉西亚和中美洲地区的事件之外，大约在同一时间发生的较小碰撞创造了塔斯马尼亚的达尔文陨石坑。 “这些冲击熔融玻璃的分布和散落区的大小表明，与地球撞击的星体至少有一公里大小，并且在冲击后几秒内释放出了令人印象深刻的一百万吨TNT能量”，施瓦茨博士解释说。据这些科学家称，后果是可怕的。 在局部地区，冲击地点周围数百公里范围内会发生火灾和地震; 对海洋的撞击会造成数百米高的海啸。在全球范围内，灰尘和气体被喷射到大气的上层，阻挡阳光并降低地表温度。 据科学家说，尽管生物的生长也受到影响，但并没有像大约6500万年前的恐龙一样，发生全球性的大规模生物灭绝。
原文如下：
Multiple Cosmic Impacts 790,000 Years Ago
Press Release No. 25/2016
22 February 2016
Heidelberg researchers determine age of rock glasses from Heidelberg researchers determine age of rock glasses from various parts of the world.
Tektite from Australia with flanged edge. The force of the impact blew the glass body thousands of kilometres and out of the earth's atmosphere. The bulging edge formed when the partially molten tektite re-entered the atmosphere.
Approximately 790,000 years ago there were multiple cosmic impacts on earth with global consequences. Geoscientists from Heidelberg University reached this conclusion after dating so-called tektites from various parts of the world. The research group under the direction of Prof. Dr. Mario Trieloff studied several of such rock glasses, which originated during impacts of asteroids or comets. The Heidelberg scientists employed a dating method based on naturally occurring isotopes that allowed them to date the tektites more accurately than ever. Their studies show that the samples from Asia, Australia, Canada and Central America are virtually identical in age, although in some cases their chemistry differs markedly. This points to separate impacts that must have occurred around the same time. The results of their research funded by the Klaus Tschira Foundation were published in the journal “Geochimica et Cosmochimica Acta”.
The research group at the Institute of Earth Sciences and the Klaus Tschira Laboratory for Cosmochemistry uses isotope measurements to determine the age of craters caused by the impact of extraterrestrial rocks. “That's how we know when, where and how often projectiles struck the earth, and how big they were,” says Mario Trieloff. There have long been signs that a major event of this type took place on earth about a million years ago, according to Prof. Trieloff. This is evidenced by tektites, so-called rock glasses that arise during impact, whereby terrestrial material melts, is hurled up to several hundred kilometres and then hardens into glass.
“We have known about such tektites for some time from the Australasian region,” explains Dr. Winfried Schwarz, the study's primary author. These rock glasses form a strewn field that stretches from Indochina to the southernmost tip of Australia. Smaller tektites, known as microtektites, were also discovered in deep-sea drill cores off the coast of Madagascar and in the Antarctic. The rock glasses had been strewn over 10,000 kilometres, with some of them even leaving the earth's atmosphere. Using the 40Ar-39Ar dating method, which analyses the decay of the naturally occurring 40K isotope, the Heidelberg researchers succeeded in dating these tektites more accurately than ever before.
“Our data analysis indicates that there must have been a cosmic impact about 793,000 years ago, give or take 8,000 years,” explains Winfried Schwarz. The Heidelberg scientists also studied samples from Canada and Central America. The Canadian rock glasses had the same chemical composition and age as the Australasian tektites and could have covered similar “flight routes” as objects found in southern Australia or the Antarctic. Other finds must first confirm whether the recovery sites are really where the tektites originally landed or whether they for example were carried there by people, according to Dr. Schwarz.
The rock glasses from Central America are also tektites – the first specimens were found at Mayan sites of worship. In the meantime, hundreds of other finds have been made in Central America. “These tektites are clearly different in their chemical composition, and their geographical distribution also shows that they come from separate impacts,” explains Dr. Schwarz. “Surprisingly our age estimates prove that they originated 777,000 years ago with a deviation of 16,000 years. Within the error margin, this matches the age of the Australasian tektites.”
These findings led the Heidelberg researchers to conclude that there were multiple cosmic impacts approximately 790,000 years ago. In addition to the events in the Australasian and Central American regions, a smaller collision at around the same time created the Darwin crater in Tasmania. “The distribution of the tektites and the size of the strewn field indicate that the earth-striking body was at least a kilometre in size and released an impressive one million megatons of TNT energy within seconds of impact,” explains Dr. Schwarz.
According to the scientists, the consequences were dire. At the local level, there was fire and earthquakes for hundreds of kilometres surrounding the impact site; an ocean impact would have caused tsunamis hundreds of metres high. At the global level, dust and gases were ejected into the upper levels of the atmosphere, blocking sunlight and lowering surface temperatures. Biomass production was also affected, although according to the scientists it did not result in global mass extinction as in the case of the dinosaurs approximately 65 million years ago.
Editor: Email
Latest Revision: 2016-12-01
来自澳大利亚的带有边缘的熔融石。冲击的力量将玻璃体吹出数千公里到地球大气层之外。 部分熔融的玻璃再次进入大气时形成的凸起边缘。
|
|Archiver|手机版|中陨网✪国陨网
( 冀ICP备10012798号-1 )
发表于 2018-5-10 11:03:43
发表于 2018-5-10 21:39:17
发表于 2018-5-16 16:11:58
