火星首現湖岸線 可能存在生命跡象

US researchers have uncovered traces of an ancient lake on Mars boosting hopes of discovering evidence that billions of years ago the Red planet hosted life.

The lake, which dates back some 3.4 billion years, appears to have covered as much as 80 square miles and was up to 1,500 feet deep, said the team from the University of Colorado.

"This is the first unambiguous evidence of shorelines on the surface of Mars," said Boulder's research associate, Gaetano Di Achille, in a study published in the latest edition of Geophysical Research Letters.

"The identification of the shorelines and accompanying geological evidence allows us to calculate the size and volume of the lake, which appears to have formed about 3.4 billion years ago."

Analysis of the images has shown the water carved out the canyon in which it was found, which then opened out into a valley depositing sediment which formed a delta.

"Finding shorelines is a holy grail of sorts to us," said assistant professor Brian Hynek, adding it showed the lake existed at a time when Mars was thought to have been cold and dry.

Scientists believe the oldest surfaces on Mars formed during the wet and warm era known as the Noachan epoch, about 4.1 billion to 3.7 billion years ago, that featured a bombardment of large meteors and extensive flooding.

The newly discovered lake is believed to date from the Hesperian era and postdates the end of the warm and wet period on Mars by 300 million years, according to the study.

Scientists believe deltas next to the lake may well hold secrets about past life on Mars as such places on Earth have become the natural deposits of organic carbon and other markers of life.

美國研究人員日前在火星上找到了一個古老湖泊的痕跡。這使人們在該紅色星球上發現數十億年前生命跡象的希望大大增強。

美國科羅拉多大學的研究小組稱，科學家發現的湖泊距今已有34億年曆史，佔地80平方英里，深達1500英尺。

科羅拉多大學波爾得分校的研究助理蓋塔諾•迪亞克雷在研究報告中稱：“這是首個證明火星表面有湖岸線的確鑿證據。”這項研究成果在最新一期《地球物理學研究快報》上發表。

“湖岸線以及其它地質證據的發現，使我們可以計算湖泊的大小和容積。這個湖泊距今約有34億年曆史。”

對成像的分析顯示，水流沖刷出了一條溪谷，這條溪谷與一個山谷相連，流水沉積物還形成一個的三角洲。

助理教授布萊恩•海尼克說： “對我們來說，在火星上發現湖岸線是一項重大收穫。”他還補充稱，研究表明湖泊存在於人們所認爲的火星寒冷乾旱期。

科學家認爲，火星最古老的表面是在溫暖溼潤的諾亞坎時期形成的，距今約41億到37億年，這一時期火星表面遍佈巨大的隕石坑和龐大的水系。

該研究表明，最新發現的這一湖泊是在赫斯伯利亞紀時期形成的，比火星溫暖溼潤季的結束還晚3億年。

科學家認爲，湖泊附近的三角洲可能完好地保存有生命存在的祕密，因爲地球上類似的三角洲也是有機碳和其它生命標誌物的天然寄存地。

Vocabulary:

holy grail：(傳說耶穌在最後晚餐中用的)聖盃，聖盤

postdate: to occur later than; follow in time（在……之後到來, 填遲……的日期）