DIGGING in dirt and rock is big business. If you dig deep enough, with luck, you will strike oil or gas, which are used as our main sources of fuel and energy.

　　Until now, we have only explored the Earth's outer layer, the crust. Oil and gas wells normally go no deeper than about six kilometres. But as these stocks rapidly decrease a new study has shown that natural gas, mainly methane¹, could be found deeper, within the Earth in the mantle². This means that new sources of energy could lie at depths of 100 kilometres or more.

　　Oil and gas found near the earth's surface are often described as fossil fuels. Most scientists believe that these fuels were formed by the breakdown³ of ancient plants and animals. But, the recent research shows that methane gas can form in the crust where there are no living creatures.

　　Researchers from Indiana University, in the US, wondered if this could also happen deeper down in the earth. They did an experiment to simulate the effects of extreme heat and pressure in the mantle on the materials found there.

　　The experiment produced tiny bubbles of methane gas, the scientists reported. But, no one knows yet how much methane, if any, is actually present in the mantle. If it is present, it could seep⁴ into the crust and escape through the ocean floor.

　　The research could provide important clues as to how life began on the Earth. Some bacteria feed on methane. If methane were present in the mantle, it could support populations of microbes, allowing them to survive in such an extreme environment. Stores of methane on Mars and other planets could show the possibility of life there too.

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　　在泥土和岩石构筑的地表中进行挖掘工作，有时是收益颇丰的。如果你挖得够深，就可能挖到石油或者天然气。这些东西都是人类的主要燃料和能源。

　　迄今为止，人类的探测范围也只是局限在地球的表层，也就是地壳。一般来说，石油、天然气蕴藏在地下六千米之内。随着这些能源的储量迅速地枯竭，人们开始把目光投向地球更深处。一项研究表明，天然气（主要成分是甲烷）有可能存在于地球深处的地幔之中。换句话说，地下100公里的地方有可能存在天然气。

　　在地表附近获取的油气资源通常被称为化石燃料。大多数科学家认为，化石燃料是大量远古动植物遗体被分解而形成的。不过，最近的研究成果表明，在没有生物存在的地壳中的某些区域里，也能找到甲烷。

　　美国印第安娜大学的研究者推测，能否可以在地球更深处找到甲烷。为了验证其推测，他们做了一个实验，模拟了一个极端高温高压的类地幔环境。

　　结果出来了，科学家们说，在实验中产生了甲烷小气泡。然而，无人知晓，如果地幔中存在甲烷的话，究竟其储量有多少。如果真的存在的话，那么，甲烷就可能渗出地壳，通过海底逸出。

　　这项研究可能为解开生命开始之迷提供重要线索。因为，一些细菌就是以甲烷卫生。如果地幔中真的存在甲烷的话，那儿说不定生活着无数的微生物。而且，火星和其它星球上也具有了生命存在的可能性。因为，这些星球上存在着大量的甲烷。