海底巨坑见证史前大撞击 Giant Craters Give Hints Of Collisions At Epic Scale 蔡继光译 马达加斯加岛南端有四个面积庞大的楔形沉积物堆积地形，沉积物都是海床物 质，叫做Ｖ状堆积。每个楔形面积约120平方公里，沉积深度约320公尺。 At the southern end of Madagascar lie four enormous wedge-shaped sediment deposits, called chevrons, composed of material from the ocean floor. Each covers an area of about 120 square kilometers, with sediment about 320 meters deep. 这些Ｖ状堆积内含已与混合金属融成一体的深海微化石。这种混合金属通常来 自宇宙撞击。所有这些证物都指向同一源头：一个新近发现，位於印度洋中央 ，在水面下四公里，直径达29公里的大坑。 The chevron deposits contain deep ocean microfossils that are fused with a medley of metals typically formed by cosmic impacts. And all of them point in the same direction － toward the middle of the Indian Ocean, where a newly discovered crater, 29 kilometers in diameter, lies four kilometers below the surface. 对一些科学家， 道理很明显。4,800年前，一个小行星或彗星撞进印度洋，制 造了浪高至少183公尺的大海啸，约为两年前淹没印尼大海啸的13倍。巨浪把 大量海底沉积物卷上陆地。 The explanation is obvious to some scientists. An asteroid or comet smashed into the Indian Ocean 4,800 years ago, creating a tsunami at least 183 meters high, about 13 times as big as the one that inundated Indonesia two years ago. The wave carried the huge deposits of sediment to land. 大多数天文学家怀疑，过去一万年间，曾有大体积的彗星或小行星击中地球。 不过，一个成立两年，自称「倒错帮」的「全新世撞击工作群」说，面对全球 海岸线和深不可测的海洋，天文学家根本不知道该如何及在何处寻找这种撞击 的证据。 Most astronomers doubt that large comets or asteroids have crashed into the Earth in the last 10,000 years. But the self-described “band of misfits” of the two-year-old Holocene Impact Working Group say that astronomers simply have not known how or where to look for evidence of such impacts along the world’s shorelines and in the deep ocean. 工作群的科学家说，一万年前的全新世撞击证据及天文学家现在的计算显示， 造成大灾难的宇宙撞击可能每数千年发生一次，而不是50万到100万年。 Scientists in the working group say the evidence for such impacts during the last 10,000 years, known as the Holocene epoch, shows that, instead of once in 500,000 to one million years, as astronomers now calculate, catastrophic impacts could happen every thousand years. 工作群科学家来自美国、澳洲、俄罗斯、法国和爱尔兰，研究领域遍及地质学、 地球物理学、地形学、海啸、年轮学、土壤学及考古学。 The researchers are based in the United States, Australia, Russia, France and Ireland. They are experts in geology, geophysics, geomorphology, tsunamis, tree rings, soil science and archaeology. 今年，工作群开始运用Google Earth提供的免费卫星影像服务，搜寻他们视同 史上大海啸爆发证据的Ｖ状堆积。澳洲、非洲、欧洲和美国找到数十个条件相 符的地点。 This year the group started using Google Earth, a free source of satellite Images, to search for chevrons, which they interpret as evidence of past giant tsunamis. Scores of such sites have turned up in Australia, Africa, Europe and the United States. 所有V状堆积都指向同一个开放水域，纽约帕利沙迪斯「拉蒙特－多赫提地球 观测所」副研究员达拉丝‧阿伯特於是采用一种不同的卫星科技来搜寻海底坑 洞。藉着逐渐升高的频率，她找到了，包括一个4,800年前的特大号坑洞。 When the chevrons all point in the same direction to open water, Dallas Abbott, an adjunct research scientist at Lamont-Doherty Earth Observatory in Palisades, New York, uses a different satellite technology to look for oceanic craters. With increasing frequency, she finds them, including an especially large one dating back 4,800 years. 美国航空暨太空总署位於加州山景市艾姆斯研究中心的小行星及彗星权威大卫‧ 莫利森说，天文学家虽然存疑，仍乐於检视证据。调查显示，远古时代，多达 185个大号的小行星或彗星击中地球，这些坑洞大多在陆地发现。莫利森说，向 来没有人多花工夫在深海找坑洞。 Astronomers are skeptical but are willing to look at the evidence, said David Morrison, a leading authority on asteroids and comets at the NASA Ames Research Center in Mountain View, California. Surveys show that as many as 185 large asteroids or comets hit the Earth in the far distant past, although most of the craters are on land. 拉蒙特观测所海洋地质学家威廉‧莱恩说：「我们当中很多人认为，达拉丝真 的做了一件了不起的大事。她建构的故事直追华特‧阿弗雷兹。」阿弗雷兹是 柏克莱加大地球与行星学教授，他提出6,500万年前一颗庞大的小行星导致恐龙 灭绝的理论，花10年工夫才说服怀疑派。 No one has spent much time looking for craters in the deep ocean, Dr. Morrison said. “Many of us think Dallas is really onto something,” said William Ryan, a marine geologist at the Lament Observatory. “She is building a story just like Walter Alvarez did.” Dr. Alvarez, a professor of earth and planetary sciences at the University of California, Berkeley, spent a decade persuading skeptics that a giant asteroid wiped out the dinosaurs 65 million years ago. 澳洲新南威尔斯卧龙岗大学地形学家泰德‧布莱恩是认出超级大海啸掌印的第 一人。他说，浪高九公尺或以上的大海啸，原因不外火山爆发、地震或海底山 崩，其沉积物特徵各异。 Ted Bryant, a geomorphologist at the University of Wollongong in New South Wales, Australia, was the first person to recognize the palm prints of mega-tsunamis. Large tsunamis of nine meters or more are caused by volcanoes, earthquakes and submarine landslides, he said, and their deposits have different features. 布莱恩说，超级大海啸所形成的沉积物，有内含牡蛎壳的罕见岩石，无法用风 化、巨浪、火山爆发或其他自然演化过程来解释。 Deposits from mega-tsunamis contain unusual rocks with marine oyster shells, which cannot be explained by wind erosion, storm waves, volcanoes or other natural processes, Dr. Bryant said. 布莱恩说：「我们所谈的，不是大家见过的任何海啸。当今没有任何海啸能制 造这些特徵。亚齐的海啸只算个酒涡。世界末日电影拍不出这种巨浪的气势。 海底山崩足以造成大海啸，但影响是局部的。超级大海啸卷起的沉积物遍及全 球海岸线。」 “We’re not talking about any tsunami you’ve ever seen,” Dr. Bryant said. “Aceh was a dimple. No tsunami in the modern world could have made these features. End-of-the-world movies do not capture the size of these waves. Submarine landslides can cause major tsunamis, but they are localized. These are deposited along whole coastlines.” 阿伯特和她的同仁在加勒比海、苏格兰、越南、北韩及北海若干地点找到许多 Ｖ状堆积。其中以马达加斯加最符合最近宇宙撞击的地质特徵。 Dr. Abbott and her colleagues have located chevrons in the Caribbean, Scotland, Vietnam and North Korea, and several in the North Sea. But Madagascar makes the best case for geologically recent impacts. 位於马达加斯加Ｖ状堆积东南方约1,450公里的深海底下，就是阿伯特去年发现 的伯克尔坑。 大坑的沉积物迄未直接取样，但该区核心已被测出含有丰富的镍，以及和撞击 喷出物有密切关联的磁性成分。伯克尔坑形成的年代迄未确定，但阿伯特估计 约在4,500至5,000年左右。 About 1,450 kilometers southeast from the Madagascar chevrons, in deep ocean, is Burckle crater, which Dr. Abbott discovered last year. Although its sediments have not been directly sampled, cores from the area contain high levels of nickel and magnetic components associated with impact ejecta. Burckle crater has not been dated, but Dr. Abbott estimates that it is 4,500 to 5,000 years old. 威廉．莱恩说，如果国家科学基金会能派有声波探测仪的船只去伯克尔探勘， 就可帮上大忙。 他说：「如果它确有明显的撞击特徵，不信的人就不得不信了。」 It would be a great help if the National Science Foundation sent a ship with acoustic equipment to take a closer look at Burckl e, Dr. Ryan said. “If it had clear impact features, the nonbelievers would believe,” he said. Ocean Secrets Scientists are scouring coastlines and oceans for signs of ancient asteroids and comets that made sea landings. Large ocean impacts could cause tsunamis, which may be responsible for chevrons, large wedge-shaped sediment deposits. Finding the crater Chevrons are angled in the direction from which they came. Once scientists know where to look, they use satellites to determine the geography of the ocean floor and find the crater. By SANDRA BLAKESLEE 关键字句 地质年代（geologictime / epoch）有特殊术语，如太古（eon）、代（era）、 纪（period）、世（epoch）等。本文所指的地质年代在全新世（Holocene epoch）是构成第四纪的两个世中年代较晚的一个，而且是地球地质史的最後 阶段。若是普通的时间术语，则period指与时间长短无关的期间，era指有根 本变化，或重要事件特徵的时代，epoch指era的新兴时期，age指具有特色或 由权势人物所代表的时代。 Sediment是被风吹、水浸或冰河冲刷而沉在下方的物质；deposits指沉底或 堆积的状态 。Sediment deposits指原本淤积在水底，被冲起後，再度淤积在别处的沉积 物。 作者对海啸（ tsunamis）做了有趣的区分， 因地震（earthquake）， 火山爆发（volcano eruptions）、海底山崩（submarince landslides）造成 的海 啸，叫大海啸（large tsunamis），这在大家理解的范围，也是所谓世界 末日电影营造得出的场景；但是造成恐龙灭绝（extinction of dinosaur）的 超级大海啸（mega-tsunami）则迄今人类未曾见过，高度超过183公尺的巨浪， 才是真正的涛天，当然可以把海底的沉积物卷到全球各地，不过，这种浪的可 怕程度，恐怕远超过我们的想像。 （蔡继光） 【2006-11-27/联合报/B6版/UNITED DAILY NEWS】 -- 赵客缦胡缨 吴钩霜雪明 银鞍照白马 飒沓如流星 十步杀一人 千里不留行 事了拂衣去 深藏身与名 闲过信陵饮 脱剑膝前横 将炙啖朱亥 持觞劝侯赢 三盃吐然诺 五岳倒为轻 眼花耳热後 意气素霓生 救赵挥金槌 邯郸先震惊 千秋二壮士 烜赫大梁城 纵使侠骨香 不惭世上英 谁能书合下 白首太玄经 李白 侠客行 --

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