An otherworldly landscape
In the Qaidam Basin on the Tibetan Plateau, at an altitude of about 3,200 meters, lies the Dachaidan Salt Lake. This is one of the highest and driest deserts on Earth. The basin itself is vast, covering around 120,000 square kilometers, and is a region of interior drainage, meaning its rivers flow into salt lakes and swamps with no outlet to the sea. The result is a hyper-arid environment where annual evaporation of 3,000-3,200 mm far exceeds the annual rainfall of less than 26 mm.
The lake is a magnesium sulfate subtype hypersaline lake, its chemistry shaped by the surrounding geology and intense evaporation. The brine contains high concentrations of lithium, boron, potassium, and magnesium, making it a target for mineral extraction. The entire base of the Qaidam Basin is covered by hundreds of meters of evaporative salt crust, rich in minerals like gypsum and halite (rock salt). This extreme environment, with its thin atmosphere, low temperatures, and UV radiation, is inhospitable to most life forms, yet it is precisely these conditions that make it a compelling location for scientific study.
Architects of a microbial world
The most fascinating inhabitants of Dachaidan Salt Lake are not visible to the naked eye. They are communities of extremophiles—organisms that thrive in harsh conditions—which form layered structures known as microbial mats. These mats are complex ecosystems dominated by halophilic (salt-loving) archaea and bacteria. Studies of the lake have isolated hundreds of strains of halophilic archaea belonging to the class Halobacteria. The dominant genus found is Halorubrum, but others like Haloarcula, Halobacterium, and Natrinema are also present.
These microorganisms are adapted to survive intense salinity and UV radiation. Many produce carotenoid pigments, which give the brine and salt crusts a distinct pink or red hue, a feature seen in hypersaline lakes around the world. The microbial mats they build are modern analogs of stromatolites, some of the most ancient signs of life on Earth, with a fossil record stretching back 3.5 billion years. The microbes, particularly photosynthetic cyanobacteria in the upper layers, trap and bind sediment and induce the precipitation of minerals from the brine, building the mat layer by layer. This process creates a stratified structure with distinct chemical gradients, where different microbial groups perform different metabolic functions at various depths.
Scientists study these mats as natural laboratories for understanding early life on Earth. The harsh and saline conditions may mirror those of the planet's Precambrian oceans. The structures also serve as a critical analog in the search for extraterrestrial life. The chemical, mineral, and isotopic fingerprints left behind by these microbes are known as biosignatures. By studying how these biosignatures are formed and preserved in Dachaidan's salt and mineral crusts, astrobiologists can refine their strategies for detecting signs of past or present life on Mars, where similar saline lakebeds and sulfate-rich deposits exist.