That's because there is often water under the rock.

那是因为岩石下面经常有水。

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However, if the planet is in a good position, astronomers look for three key things: water, air and rock.

然而如果这颗行星处于很好的位置，天文学家会寻找三样关键的东西：水、空气和岩石。

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Part of the limestone rock layer is permeated by water from below.

下面的水渗入了部分石灰岩岩层。

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They drill down to the shale, then go sideways and inject high-pressure water, sand or other material into the rock.

VOA: special.2009.10.23

The action of wind and water can form cave openings like natural rooms within the rock.

VOA: special.2009.07.20

It takes centuries for water dripping through the rock to make these beautiful formations.

VOA: special.2009.07.20

"These are microbes that can survive on the energy from the natural water-rock interactions, " he told BBC News.

BBC: Deep Canadian mine yields ancient water

Getting at the oil can be tricky, and not just because it lies under as much as 9, 000 meters of water and rock.

FORBES: Going deep

To do so they're pushing the frontiers of imaging technology to peer beneath miles of water, rock and salt layers thousands of feet thick--all in the hopes of finding billions of barrels of oil trapped below.

FORBES: Magazine Article