英语听力：自然百科 墨西哥湖泊与生命的启示（在线收听）

 The small town of Cuatro Cienegas in northern Mexico is an oasis (绿洲) in the Chihuahuan desert. It’ s a valley that holds an example of what some believe is the one of the first human footprints in the Americas(美洲大陆以及附近岛屿) along with cave paintings produced by the first people who walked through this valley.

These rock paintings were made with iron oxides(铁的氧化物), some plant extracts and even with some drops of blood. These have their origins in the first settlers of America ten thousand years ago.

Cuatro Cienegas fosters a unique ecosystem from prehistoric times and the research done here has enlightened scientists and historians.

We have tracked only the history of organisms when the sea existed here 200 million years ago, but also the very same environmental conditions as the ones when life began on earth 35 to 38 hundred million years ago. So this is a time machine, and it is the only one we have on earth.

To find the secrets of the valley, scientists carried out experiments in the four large ponds for which the areas named. Samples of fossilized algae(海藻), known as stromatolites(叠层石), are taken back to laboratory so scientists can grow the microorganisms they discovered in the wild.

By extracting DNA from stromatolite, the scientists hope to gain insight into the effects and causes of global warming. Reportedly results have already revealed how marine fish and turtles adapted to live in fresh water.

Each one of these wells has a unique history just as the Galapagos Islands(加拉帕哥斯群岛，位于厄瓜多尔西部，拥有多种独特生物，达尔文在岛上的考察成果成为进化论的重要依据). What we are trying todecode here is the origin of the species that Darwin overlooked--the origin of the small species.

The American space agency NASA also has a special interest in Cuatro Cienegas.

Microbial(微生物的) life here dominates and if we are going to find life on Mars it’ll probably be microbial life, so if we understand life here in this place we might be able to understand how to find it on Mars.

Despite the fact that UNESCO is calling for a Cuatro Cienegas’s conservation, its future is not secure. Irrigation for agriculture and cattle grazing, as well as poorly managed development in tourism, all threaten this important area. This makes responsible ecotourism all the more(更加，加强语气) important to the town’s people. The local government insists it’s trying to strike a balance between the needs of the residents and the need to preserve the region for future generations.