Magazine article Americas (English Edition) , Vol. 62, No. 4
The high mountain desert of Coahuila, Northern Mexico is a seemingly lifeless environment that, like any extreme environment, is brutally honest. Temperatures typically exceed 115[degrees]F with precipitation averaging less than eight inches annually. Yet, lying within this harsh confine is a truly unique ecosystem of freshwater biodiversity and geological oddity. It is one of the few places left on earth where you can still find traces to early life, surviving strangely enough in what appear to be ordinary rocks.
The Cuatro Cienegas valley is a scenic marvel of white gypsum dunes and desert gardens in the heart of the Chihuahuan Desert. Surrounded by mountains rising over 9,000 feet above sea level, this 200,000-acre valley contains hundreds of freshwater springs that rival any ocean lagoon in contrasting beauty, truly epitomizing the "oasis in the desert." Spanish settlers named the valley's town Cuatro Cienegas, meaning "four marshes," due to its proximity to these natural springs, and today the region is gaining international recognition for its unique ecosystem.
Cuatro Cienegas has been described as one of North America's rarest environments. Paradoxically labeled a desertwetland, the region contains a system of subterranean water channels that feed a series of springs, streams, and pools in one of North America's driest--if defined by precipitation--climates. These waters possess a diversity of qualities, from clear to turbid, thermal to cool, and freshwater to water with high concentrations of minerals. And, the region is the only place in Mexico with gypsum dunes, which are created as high winds deposit the precipitate from a neighboring lake. It is a geological rarity to find gypsum in sand form, since it dissolves easily in water and usually finds a path to the ocean.
Species unique to a particular geographic location--known as endemic species--are prevalent on islands due to their physical isolation. Yet, the Cuatro Cienegas valley has its own set of "islands" in the form of spring-fed pools called pozas. For millennia, the geographical isolation and water variation has created distinct habitats. The result? The valley boasts the highest level of endemic biodiversity in all of North America, with over 70 endemic species of aquatic invertebrates and vertebrates. This is a crowning achievement considering its desert climate, inland location, and low overall level of biodiversity. Nearly all of the fish species are endemic with some sharing a lineage with either Neotropical or Nearctic fish. Interestingly, investigations into the invisible world of microbes show unique bacterial and viral communities that are only distantly related to marine microbes, reflecting an ancient marine origin. The high incidence of endemism includes a majority of the freshwater invertebrates anti also extends to several other plant and animal species.
One of the most unique features found in the freshwater habitat of Cuatro Cienegas are living, rock-like structures called microbialites. Depending on hydrological influences, their size and shape can vary from wide expanses of soft mats, to colossal size mounds, to relatively diminutive round bails called oncolites that quietly roll down the river. In some instances, these structures are reminiscent of coral reefs with impressive wall formations that fringe along the passage of a poza, surrounded by passing fish and emerald waters. Microbialites are essentially living rocks formed by a complex community of microorganisms. Each microbialite structure is an organic deposit of sediment, trapped and bound by the mineral accretion of microbes that live within.
These peculiar objects were the keystone in making Earth hospitable for life by playing a central role in the developmerit of oxygen in the planet's atmosphere three billion years ago. Prior to that time, the atmosphere was dominated by carbon dioxide, and simple-celled organisms thrived in the anaerobic environment. …