It is beneficial to dig in dirt and the surface formed by rocks sometimes. If you dig deep enough， you will strike out oil or gas， which are used as our main sources of fuel and energy.
Until now， we have only explored the outer layer of the Earth， i.e. the crust. Oil and gas are mined under the earth within about six kilometers. But as these stocks rapidly decrease， people would focus on a deeper depth of the earth. Natural gas whose main make-up methane① could be found deeper within the Earth in the mantle②. In other words， new sources of energy could lie at depth of 100 kilometers 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 breakdown of ancient plants and animals. But， the methane gas can be found in the crust③ where there are no living creatures now.
Researchers from Indiana University， in the US， wondered if this could also happen deeper down in the earth. They did an experiment to simulate④ the effects of extreme heat and pressure in the mantle on the materials found there.
How much methane is there in mantle if it is actually present？ If it is present， it could seep into the crust and escape through the ocean floor.
If it is possible， it is an important clue to how life began on the Earth. This is because some bacteria live on methane. If methane were present in the mantle， it could support populations of microbes⑤， allowed to survive in such an extreme environment. Stores of methane on Mars and other planets could show the possibility of life there too. The reason is that there are a lot of methane.
① methanen. ［化］甲烷，沼气
② mantlen. ［地］地幔
③ crustn. 地壳
④ simulatev. 模仿，模拟，看上去像
⑤ microben. 微生物，(尤指引起疾病的)细菌［C］
人类在地幔中找燃料
有时在泥土和岩石构筑的地表中进行挖掘工作的收益是颇丰的。如果挖得够深，就有可能挖到是人类的主要燃料和能源的石油或者天然气。
迄今为止，人类也就只是探测到地球的表层，即地壳。一般来说，石油、天然气蕴藏在地下6千米之内。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。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100千米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，在没有生物存在的地壳中的某些区域里，也能找到甲烷。
如果地幔中存在甲烷的话，其储量究竟有多少？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。
如果可能的话，生命开始之迷就会有重要线索。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。
