He wears gloves and cleans his tools with alcohol to avoid contaminating the ancient salt samples with modern microorganisms.

"The salt round about us was crystallized out 260 million years ago, and 260 million years ago, organisms in this salt lake contributed towards the crystallization. And they became incorporated in the salt. We've taken samples of the salt back to a laboratory, and we carefully dissolve away the mineral part of the material and we feed the sample with nutrients that we know encourage the growth of these special bacteria. And indeed from some of the samples, we were able to hatch out viable bacteria that might be 260 million years old.

If ancient bacteria can be revived on earth, this may also be possible on Mars.

"Mars, many millions of years ago, had water, lakes, rivers and presumably salt lakes. And perhaps, on Mars, the salt lakes harbored populations of creatures like the ones on earth. So if one is going to look for life on Mars and our earthly experience down here is anything to go by, where better to look for life than salt deposits on Mars.

The more examples of life surviving in a dormant state in harsh earthly environments, the better chance of finding it on Mars. Life has a way of hanging on, from the heat of an ancient salt deposit to the freezing cold of Antarctica. A lone scientist stalks the vast plains of the southern continent. Professor E. Imre Friedmann is looking for rocks, rocks that hold some of the hardiest microbes on earth. It's not as cold as Mars here, but almost. In his giant freezer at the Florida State University in Tallahassee, Professor Friedmann keeps over 300 samples of bacteria found in rocks around the world. The bacteria are removed from rock in his laboratory.

"and we collected this rock in the Antarctic desert and this is a rock which is colonized by microorganisms. The surface is lifeless, but under the surface, here, microorganisms exist which can be seen in this black zone and the leached white zone. The surface of that rock is also to isolate the microorganisms in this laboratory and grow them. We'll transfer pieces into the sterile medium.

One day, we may isolate sleeping Martians in a similar way.

"I m putting this enrichment culture here in the light because these microorganisms like plants need sunlight. This is a rock which has been placed here about two months ago.

Here are the bacteria that have thrived in some of the toughest cold conditions that...

words in this passage

crystallize: If a liquid crystallizes, it turns into crystals.结晶

stalk:昂首阔步；大步走

leach:to remove a substance from a material, especially from earth, by the process of water moving through the material, or to remove parts of a material using water:滤去

sterile:completely clean and free from dirt and bacteria:无细菌的；消毒的