海底巨坑見證史前大撞擊 Giant Craters Give Hints Of Collisions At Epic Scale 蔡繼光譯 馬達加斯加島南端有四個面積龐大的楔形沉積物堆積地形，沉積物都是海床物 質，叫做Ｖ狀堆積。每個楔形面積約120平方公里，沉積深度約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. 這些Ｖ狀堆積內含已與混合金屬融成一體的深海微化石。這種混合金屬通常來 自宇宙撞擊。所有這些證物都指向同一源頭：一個新近發現，位於印度洋中央 ，在水面下四公里，直徑達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. 對一些科學家， 道理很明顯。4,800年前，一個小行星或彗星撞進印度洋，製 造了浪高至少183公尺的大海嘯，約為兩年前淹沒印尼大海嘯的13倍。巨浪把 大量海底沉積物捲上陸地。 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. 大多數天文學家懷疑，過去一萬年間，曾有大體積的彗星或小行星擊中地球。 不過，一個成立兩年，自稱「倒錯幫」的「全新世撞擊工作群」說，面對全球 海岸線和深不可測的海洋，天文學家根本不知道該如何及在何處尋找這種撞擊 的證據。 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. 工作群的科學家說，一萬年前的全新世撞擊證據及天文學家現在的計算顯示， 造成大災難的宇宙撞擊可能每數千年發生一次，而不是50萬到100萬年。 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. 工作群科學家來自美國、澳洲、俄羅斯、法國和愛爾蘭，研究領域遍及地質學、 地球物理學、地形學、海嘯、年輪學、土壤學及考古學。 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，工作群開始運用Google Earth提供的免費衛星影像服務，搜尋他們視同 史上大海嘯爆發證據的Ｖ狀堆積。澳洲、非洲、歐洲和美國找到數十個條件相 符的地點。 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狀堆積都指向同一個開放水域，紐約帕利沙迪斯「拉蒙特－多赫提地球 觀測所」副研究員達拉絲‧阿伯特於是採用一種不同的衛星科技來搜尋海底坑 洞。藉著逐漸升高的頻率，她找到了，包括一個4,800年前的特大號坑洞。 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. 美國航空暨太空總署位於加州山景市艾姆斯研究中心的小行星及彗星權威大衛‧ 莫利森說，天文學家雖然存疑，仍樂於檢視證據。調查顯示，遠古時代，多達 185個大號的小行星或彗星擊中地球，這些坑洞大多在陸地發現。莫利森說，向 來沒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. 拉蒙特觀測所海洋地質學家威廉‧萊恩說：「我們當中很多人認為，達拉絲真 的做了一件了不起的大事。她建構的故事直追華特‧阿弗雷茲。」阿弗雷茲是 柏克萊加大地球與行星學教授，他提出6,500萬年前一顆龐大的小行星導致恐龍 滅絕的理論，花10年工夫才說服懷疑派。 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. 澳洲新南威爾斯臥龍崗大學地形學家泰德‧布萊恩是認出超級大海嘯掌印的第 一人。他說，浪高九公尺或以上的大海嘯，原因不外火山爆發、地震或海底山 崩，其沉積物特徵各異。 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. 布萊恩說，超級大海嘯所形成的沉積物，有內含牡蠣殼的罕見岩石，無法用風 化、巨浪、火山爆發或其他自然演化過程來解釋。 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. 布萊恩說：「我們所談的，不是大家見過的任何海嘯。當今沒有任何海嘯能製 造這些特徵。亞齊的海嘯只算個酒渦。世界末日電影拍不出這種巨浪的氣勢。 海底山崩足以造成大海嘯，但影響是局部的。超級大海嘯捲起的沉積物遍及全 球海岸線。」 “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、蘇格蘭、越南、北韓及北海若干地點找到許多 Ｖ狀堆積。其中以馬達加斯加最符合最近宇宙撞擊的地質特徵。 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. 位於馬達加斯加Ｖ狀堆積東南方約1,450公里的深海底下，就是阿伯特去年發現 的伯克爾坑。 大坑的沉積物迄未直接取樣，但該區核心已被測出含有豐富的鎳，以及和撞擊 噴出物有密切關聯的磁性成分。伯克爾坑形成的年代迄未確定，但阿伯特估計 約在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．萊恩說，如果國家科學基金會能派有聲波探測儀的船隻去伯克爾探勘， 就可幫上大忙。 他說：「如果它確有明顯的撞擊特徵，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 關鍵字句 地質年代（geologictime / epoch）有特殊術語，如太古（eon）、代（era）、 紀（period）、世（epoch）等。本文所指的地質年代在全新世（Holocene epoch）是構成第四紀的兩個世中年代較晚的一個，而且是地球地質史的最後 階段。若是普通的時間術語，則period指與時間長短無關的期間，era指有根 本變化，或重要事件特徵的時代，epoch指era的新興時期，age指具有特色或 由權勢人物所代表的時代。 Sediment是被風吹、水浸或冰河沖刷而沉在下方的物質；deposits指沉底或 堆積的狀態 。Sediment deposits指原本淤積在水底，被沖起後，再度淤積在別處的沉積 物。 作者對海嘯（ tsunamis）做了有趣的區分， 因地震（earthquake）， 火山爆發（volcano eruptions）、海底山崩（submarince landslides）造成 的海 嘯，叫大海嘯（large tsunamis），這在大家理解的範圍，也是所謂世界 末日電影營造得出的場景；但是造成恐龍滅絕（extinction of dinosaur）的 超級大海嘯（mega-tsunami）則迄今人類未曾見過，高度超過183公尺的巨浪， 才是真正的濤天，當然可以把海底的沉積物捲到全球各地，不過，這種浪的可 怕程度，恐怕遠超過我們的想像。 （蔡繼光） 【2006-11-27/聯合報/B6版/UNITED DAILY NEWS】 -- 趙客縵胡纓 吳鉤霜雪明 銀鞍照白馬 颯沓如流星 十步殺一人 千里不留行 事了拂衣去 深藏身與名 閒過信陵飲 脫劍膝前橫 將炙啖朱亥 持觴勸侯贏 三盃吐然諾 五嶽倒為輕 眼花耳熱後 意氣素霓生 救趙揮金槌 邯鄲先震驚 千秋二壯士 烜赫大梁城 縱使俠骨香 不慚世上英 誰能書閤下 白首太玄經 李白 俠客行 --

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