From a Mexican swamp to life on Mars

How 170 lagoons in the Chihuahua desert of Mexico may tell us about life on other planets. Tim Gaynor and Andrew Gumbel report

The Chihuahua desert, in northern Mexico, may not sound like the obvious place for scientists to hunt down the origins of life, but that's because most people have never heard of the archipelago of strange, soupy lakes known as the Cuatro Cienegas.

The Chihuahua desert, in northern Mexico, may not sound like the obvious place for scientists to hunt down the origins of life, but that's because most people have never heard of the archipelago of strange, soupy lakes known as the Cuatro Cienegas.

To a handful of dedicated scientists who have been making the journey for years across Coahuila province's barren landscape of mesquite-strewn sand and rock, the place is a Holy Grail. Many of them describe the 170-odd cactus-ringed pozas (ponds) and lagunas as a kind of upside-down Galapagos Islands - a teeming ecosystem of plant and animal life whose uniqueness is protected not by the raging Pacific Ocean but by hundreds of miles of arid desert.

More recently, Nasa has taken an interest too, and for an intriguing reason: the space agency believes the geological formations at Cuatro Cienegas bear a strong resemblance to the general pattern of the Earth's development in the age before the dinosaurs and might therefore be a clue to the development of living organisms - on this planet or on any other. In other words, if Nasa's Astrobiology Institute can learn to recognise the life-promoting patterns in the rocks and gases of Cuatro Cienegas, it might well be able to find the same patterns on other planets and in other galaxies.

Its researchers aren't expecting to meet Star Trek-style alien civilisations any time soon, but a few micro-organisms somewhere out there in the inky blackness of space would give them enough excitement to last a lifetime.

"They [the micro-organisms] may be our best example of what to look for on other planets," said Brad Bebout of Nasa's Ames Research Centre, as he prepared to harvest methane belched out of a shallow blue-green pool. He added: "Most of the time that life has been on Earth, this is what it looked like, not like the plants and animals that you see around you now."

The lakes are a residue left behind after the seas retreated from the area 100 million years ago. As explained by Carol Tang of the California Academy of Sciences, who has worked with Nasa on its research, Cuatro Cienegas developed in ways similar to Death Valley in California and other spots where life thrives against the climatic odds. Essentially, the water comes from heated underground springs where it has acquired unusual salts, minerals and trace elements.

That, in turn, promotes the rare forms of algae, snails and fish, many of which cannot be found anywhere else on the planet. Some are rare enough to exist in a single pool, and die if transferred to another.

What's more, Dr Tang and other scientists believe the hot aquatic habitats of Cuatro Cienegas are remarkably close to the conditions that existed on planet Earth for the first three billion or so years of its existence, when tectonic plates shifted more frequently, creating surges of molten magma and prompting proteins and amino acids to interact with each other in ways that may have promoted the first flowering of living organisms.

"Could these heat-loving microbes be similar to the ancestors of all life on Earth?" Dr Tang asked in a recent paper. "And if so, would this kind of environment also be a nursery for life on other planets?"

Of particular interest to the Astrobiology Institute are a kind of fossilised mat of algae known as stromatolites - essentially, calcified clumps of primitive bacteria that act as mini-laboratories of incipient life. Stromatolites have already been the subject of searches on Mars and other planets in our solar system.

At Cuatro Cienegas, they have been scrutinised in extraordinary detail by different groups of researchers. Dr Tang, for example, has worked with a colleague from the California Academy of Sciences called Peter Roopnarine to study indigenous snails from the genus Mexipyrgus. By studying how the snails' shells vary from one stromatolite location to another, they hope to develop theories on how their environment affects their development.

Dr Bebout has been engaged in taking a range of gas readings, cell and chemical samples from the stromatolite bacteria clusters, which looked like a strange, desert form of coral.

Nasa's plan is to use information from the samples to perfect complex computer models of atmospheric conditions suitable to life on a range of "virtual" planets. The models will be used by astronomers armed with a powerful space-based telescope - due to be launched in the next decade - to search for the unique signs of life in atmospheres surrounding far-off planets.

"We believe, and it is only a belief at this point, that there is probably a lot of life out in the universe, but it may only be at the microbial stage," Victoria Meadows, the institute's virtual planetary laboratory chief said as she watched scuba divers entering the Poza Azul lake. "Not people flying UFOs, but nevertheless life elsewhere in the universe."

Astronomers have found 145 planets beyond our solar system in the past decade. Most are lifeless giants like Jupiter and Saturn, although they say that some planetary systems might also contain smaller, terrestrial planets like Mars and Earth. Armed with a target list of about 200 stars within 45 light years of Earth that Nasa plans to study in detail, they have now begun honing their search for potentially life- bearing worlds.

Too far to visit with a space probe, astronomers plan to explore them using a space observatory dubbed the Terrestrial Planet Finder.

To be launched in 2014 and with an imaging power 100 times greater than the current Hubble Space Telescope, it is expected to send back telling snapshots of never before seen planets circling far-off stars. Astronomers plan to analyse them using a spectrometer, a machine which uses light to determine what gases are present in the planets' atmospheres, and check it against Nasa's list of characteristics for a life-bearing world.

"We won't be able to break the planet up into continents and oceans or waterfront real estate, but what we will see is a dot of light containing a lot of information about the atmosphere and surface," Dr Meadows said. "What we are learning here at Cuatro Cienegas may help us understand it."

Cuatro Cienegas lies about 150 miles south of the Texas border and attracts a steady stream of hardy tourists who don't mind bringing in their own food and camping gear. But it could hardly be described as a magnet for tourism.

Ten years ago, the Mexican government placed the area under special protection but did nothing to alter the pattern of land ownership, causing concern among environmentalists who fear that its unique features are now under threat.

The pure gypsum dunes that surround the archipelago have been steadily mined to the point where they have shrunk from 50ft down to around 20ft. Farmers have also built irrigation canals that are having an effect on water levels in the pozas.

Mexican environmental scientists say that this process needs to be reversed if Cuatro Cienegas is to be preserved. Ecotourism is the obvious answer - except that in a region deprived of government resources it is hard to see where the seed capital for the necessary hotels, roads and other infrastructure would come from.

"We risk losing one of Mexico's most precious ecosystems," the Mexican biologist Salvador Contreras Banderas said recently. Nasa may be needed in more ways than one.