阅读资料：火星首现湖岸线 可能存在生命迹象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...
