Tibetan Microbe Mats

The Taklimakan Desert in northwest China is a vast region of sand desert sitting in a depression between two high, rugged mountain ranges.
Credit: NASA

Searching for clues to the potential for life on Mars, NASA scientists recently explored microbial communities in some of the world’s oldest, driest and most remote deserts in China’s northwest region, and found evidence suggesting that conditions there may be similar to those in certain regions of Mars.

This is the first comprehensive study of microbial ecosystems in the extreme deserts of China. Scientists looked for microbial life and tried to determine climate’s effect on the distribution, diversity and abundance of that life in extreme conditions. Results of this study were published recently in the Journal of Geophysical Research.

"Our findings showed that numerous sources of water, such as rainfall and snowmelt, characterized how microbial life existed in its environment," said Chris McKay, the principal investigator at NASA Ames Research Center, Moffett Field, Calif. "Rainfall amounts primarily dictated the type of microbial ecosystems we found across sites, but the effects of temperature, humidity and light created a gradient of soil water conditions suitable for life as well," added McKay.

NASA photographs recently revealed bright new deposits seen in two martian gullies, like this one in a crater in the Centauri Montes Region. The images suggest that water carried sediment through them sometime during the past seven years.
Credit: NASA/JPL-Caltech/Malin Space Science Systems

In December 2006, NASA published satellite images from the Mars Global Surveyor mission that showed periodically changing gullies on the surface of Mars. Although no one knows for sure how the martian gullies were formed, some scientists hypothesize that they may be the result of surfacing groundwater or melting of ice in the martian subsurface.

According to McKay, single-celled organisms can exist only if there is enough water, which determines life’s limits. To study the possibilities of microbial life on Mars, scientists went to the most arid, Mars-like environments they could find on Earth – the dry valleys of Antarctica, the Atacama Desert of Chile, and now northwestern China.

Scientists who are interested in Mars and its environmental conditions have been studying microbial ecosystems in the deserts of Earth for years, focusing on blue-green algae, or cyanobacteria. The bacteria’s green color indicates they are capable of photosynthesis, the principal process by which organisms produce organic matter from inorganic matter.

According to scientists, microbial photosynthesis can occur within and under rocks in the desert. If the rock is porous, like sandstone, then cyanobacteria can live within its pores or crevices, where water can be held. More commonly, cyanobacteria are found under translucent rocks, such as quartzite, where light can penetrate, allowing photosynthesis to occur.

To broaden understanding of the dynamic physical environments that allow for microbial survival, McKay’s research team traveled to China’s extreme northwest region in the spring of 2006 for data collecting and analyses. Field locations — including Tokesun, Ruoqiang and Sorkuli – were selected based on contrasting temperatures and amounts of regional rainfall.

The Atacama desert in Chile, one of Chris McKay’s research sites, is the driest environment recorded on Earth.
Credit: Aaron Gronstal

Tokesun contains the lowest point in China, approximately 500 feet (152 m.) below sea level. It was selected because it is hot and dry. Ruoqiang runs parallel to the southern edge of the Taklimakan Desert and is hot and wet.

Sorkuli is a high-altitude desert, ranging between 8,200 feet and 9,840 feet (2500 m. to 3000 m.) that is situated along the Qinghai-Tibetan plateau. Climate conditions there vary due to changes in altitude and landscape. It has two types of environments: cold and dry, and cold and wet.

"Through a comparison of similar available climate data for other deserts, we conclude that from a microbial physiological standpoint, although the Atacama Desert represents the driest environment recorded, and the Dry Valleys in Antarctica represent the coldest desert conditions, the high-altitude deserts in the Qinghai-Tibetan Plateau represent the coldest and driest conditions recorded on Earth," said McKay.

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