University Valley, one of Antarctica’s Upper Dry Valleys, where liquid water is a scarce commodity because the ground remains frozen year-round.
Credit: M. Marinova
MARYLAND: All life as we know it needs water. But what organisms can survive when water is all but unavailable? To find out, one scientist is looking at soil from two of the driest places on Earth.
Because the surface of Mars today is bone-dry and frozen all year round, it's difficult to find any place on Earth that is truly Mars-like. But two locations, Antarctica's Upper Dry Valleys and the hyper-arid core of Chile's Atacama Desert, come close. They have become magnets for scientists who want to understand the limits of life on Earth and the prospects for life on Mars.
"What we do in those environments is try to understand who is there, what those organisms might be doing, how they are distributed," said Jocelyne DiRuggiero, associate professor of biology at Johns Hopkins University in Baltimore, Maryland, who studied samples from both locations.
She's also interested in whether the organisms are "really active metabolically", or if instead they're "just sitting there, because they've been brought by the wind".
Investigating extreme deserts
DiRuggiero's been investigating the similarities and differences between the microbial communities that live in these two extreme desert regions.
In both places, very little liquid water is present. In the core of the Atacama, years can go by between one rainfall and the next, but it is warm, so when there is precipitation, a significant amount of liquid water is available for a very short time.
In University Valley, one of Antarctica's Upper Dry Valleys, the availability of liquid water is limited in a different way. University Valley receives more regular precipitation than the Atacama, but it's so cold there that any precipitation falls in the form of snow and remains frozen.
Permanently frozen ground
DiRuggiero's primary tool is DNA sequencing. Working with soil samples that weigh one- to two-tenths of a gram each (about a teaspoonful), she extracts the DNA from any microbes present in each sample. She then sends the DNA off to a lab for sequencing.
Sample preparation is a difficult process because there aren't many microbes in her samples. Each gram of soil contains perhaps one hundred to one thousand, an extremely low number. The same size sample of ordinary soil typically contains ten million to a billion organisms.
Although she has had more time to work with samples from the Atacama, DiRuggiero said the University Valley samples are particularly interesting. Because University Valley is both near the South Pole and more than a mile above sea level, the ground there stays frozen even in summer.
There are few places in the world where this is true. "It's about 40 degrees Celsius colder than the Atacama soil," she said. That's about 70 degrees Fahrenheit colder.
