Results
from a recent study of the microbes in China's remote deserts could help astrobiologists
refine their maps for uncovering Martian life.
Ongoing
studies of Mars analogs on Earth have
combed the iciest regions and the driest areas. But the new study, published in
the Feb. 15 issue of the Journal of Geophysical Research-Biogeosciences,
is the first comprehensive look at the microbial
life in the extreme deserts of China.
"If you go
to the Dry Valleys in Antarctica, that is arguably the coldest place on Earth,
and certain areas in the Atacama Desert are some of the driest on Earth," said
lead author Kimberley Warren-Rhodes of NASA Ames Research Center.
"What we didn't
have, and which is more similar to Mars, is a combination of those conditions,"
she added, until now.
Harsh
life
Warren-Rhodes
and her colleagues, including her advisor Chris McKay of NASA Ames, examined
the abundance and diversity of blue-green algae called cyanobacteria in several
spots in the extreme deserts of China.
They chose
three locations based on temperatures and amount of rainfall. One site, called
Tokesun, was warm and dry and located about 500 feet (152 meters) below sea
level, making it the lowest point in China. Another site, called Ruoqiang, runs
parallel to the southern edge of the Taklimakan Desert and is hot and wet.
The last
site, Sorkuli, is situated along the Qinghai-Tibetan plateau and lies between
8,200 feet and 9,840 feet (2,500 meters to 3,000 meters) above sea level. This
high-altitude desert included two climates: cold and dry, and cold and wet.
Like green
plants, cyanobacteria capture the sun's energy to carry out photosynthesis and
turn inorganic ingredients into organic material needed for growth. On Earth, water is
the limiting factor for carrying out photosynthesis, and this would be
particularly true on the parched planet of Mars. But ecologists suspect that microbes
can live within rock pores or beneath translucent rocks where moisture is most
likely to remain, possibly on both planets
So the team
also used data recorders at the Chinese sites to measure "micro-climate"
conditions, including the relative humidity, moisture, temperature and light
levels in the soil, beneath rocks and within pore spaces of rocks.
An increase
in rainfall was typically associated with a spike in microbial density, but
there were other factors too. "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," McKay said.
Microbial
hideouts
The
microbes preferred some tiny homes more than others, the scientists found. "When
you start talking about microbiology in a planetary sense, we work at these
larger scales, but it's this microclimate scale that's really important to
these organisms," Warren-Rhodes said.
"We're
finding that there are certain characteristics that make it more probable to
find [microbial life] than not in these really harsh deserts," Warren-Rhodes
said. One feature is rock size, with the larger rocks supporting higher
densities of cyanobacteria, presumably because they can store more water.
"We look at
these rocks, and these are small, just tens of centimeters. But to [microbes],
that's like living on a huge mountain range," Warren-Rhodes told SPACE.com.
"Think of the variations from the top to the bottom of a mountain range and
that's what's important to these microbes."
She added, "So
we have to get into that perspective to understand the conditions that make one
habitat super-accommodating and one centimeter next door not so much."
Once life
takes hold in a hostile environment, it could change its home-base to make it
more conducive for survival. "Many of these organisms exude certain types of
material that may act as sponges in their environment," Warren-Rhodes said. The sticky substances are known as extracellular slime. "When [the substances] get wet, they swell to several times their original volume and may serve as a reservoir for water in extremely dry deserts," Warren-Rhodes explained.
The
scientists plan next to study the spatial distribution of microbes, along with
the associated climate features, in the Atacama Desert and in Antarctica.
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