英语听力：自然百科 探索世界奥秘之Life On Mars(火星生命)Unit09

The ground here is permafrost, a mixture of soil and ice frozen together. A group of Russian scientists have teamed up with NASA to drill down into it in search of microorganisms. It's work that's been done in Russia for years.

People found the microorganisms in permafrost in the end of 19th century. It was done especially in Russia when people found mammoths.

Back then it was the mammoths they were after. But David Gilichinsky's team have now drilled so deep that they've reached permafrost that was laid down millions of years ago. The frozen cores were taken back to their laboratory. Samples were taken from the centre of the core. Then they looked for signs of life. They discovered that bacteria can survive in the permafrost for far longer than anyone had thought possible. They found bacteria which may turn out to have been at minus twenty degrees for more than ten million years.

We have some data, but we are not sure 100%. But probably we have now isolated¹ bacteria from Antarctic permafrost. It's between 8 and 15 million years old.

Bacteria have been buried alive here in frozen ground since before the beginning of human evolution. If life can survive in Antarctica for 15 million years, then something could be waiting to be revived on Mars.

These discoveries put new urgency in the quest to find water on Mars. There was now a real possibility that they might find something alive. So authorisation came from the very top: send more missions to Mars. NASA launched several probes with the express purpose of mapping the composition of the Martian surface.

permafrost: Perennially² frozen earth, with a temperature below 32 °F (0 °C) continuously for two years or more. Permafrost is estimated to underlie³ 20% of the Earth's land surface and reaches depths of 5,000 ft (1,500 m) in northern Siberia. It occurs in 85% of Alaska, more than half of Russia and Canada, and probably all of Antarctica. Permafrost has a significant effect on plant and animal life, and it presents special problems in engineering projects. All land use in permafrost environments must take into account the terrain's special sensitivity; if the delicate natural balance is not maintained, extensive degradation and ecological damage may result

human revolution:Evolution of modern human beings from nonhuman and extinct hominid forms

1 isolated   

adj.与世隔绝的

参考例句：

• His bad behaviour was just an isolated incident. 他的不良行为只是个别事件。
• Patients with the disease should be isolated. 这种病的患者应予以隔离。

2 perennially   

adv.经常出现地；长期地；持久地；永久地

参考例句：

• He perennially does business abroad. 他常年在国外做生意。 来自辞典例句
• We want to know what is perennially new about the world. 我们想知道世上什么东西永远是新的。 来自互联网

3 underlie   

v.位于...之下，成为...的基础

参考例句：

• Technology improvements underlie these trends.科技进步将成为此发展趋势的基础。
• Many facts underlie my decision.我的决定是以许多事实为依据的。