And yet, there is a thriving ecosystem in the lake.
How does the lake maintain itself? What lives there? And how have these organisms adapted to the harsh conditions at the volcanos summit?
These are some of the questions that an international team of scientists, headed by Nathalie Cabrol of NASA AMES/SETI Institute in Mountain View, CA, hope to answer. In the coming weeks, they will climb to the summit, camp inside the caldera, set up a variety of scientific experiments and dive into the frigid lake to collect water and sediment samples.
Included in the expedition is a team of biologists, headed by Imre Friedmann. They will examine the organisms in the samples collected by the ascent team, using traditional taxonomic methods that is, by looking at the samples through a microscope.
Friedmann admits that DNA analysis would be "a more elegant, more exciting method of looking at things." But, he points out, "you cannot make an identification of an organism by identifying its genetic structure." Even if researchers found genetic material indicative of organisms that had never been seen before and Friedmann does expect to find such novel organisms they wouldnt know anything about what the organisms looked like or how they behaved. To determine that, Friedmann says, it is necessary to examine the organisms through the microscope, followed by isolating and growing them in the laboratory.
Natural Sunscreen
Cabrol and her colleagues are particularly interested in learning how the organisms that inhabit the lake they are mostly microorganisms survive the damaging effects of UV radiation.
Most of the Earth is covered by a protective ozone layer that screens out higher-energy UV radiation, which is particularly damaging to life. "The best way to get high UV," explains Chris McKay, a planetary scientist at NASAs Ames Research Center in Mountain View, CA, and a member of the Licancabur expedition, "is to go to high elevations. The equatorial regions are particularly interesting because the Sun is higher in the sky," so the radiation is stronger than in regions closer to the poles.
One of the experiments the ascent team will set up is designed specifically to study how the life forms in the lake respond to UV. The scientists will place several plexiglass plates on the lakebed. Some of the plates will screen UV; others will allow it to pass through. These will remain in place until next year, when a second expedition will return to examine the effect of differing amounts of UV exposure on the growth of the organisms.
Early Earth, Early Mars
Learning how the Licancabur organisms protect themselves from UV may help researchers understand how life survived on early Earth and perhaps on early Mars as well.
Most scientists believe that, for perhaps as long as two billion years after life emerged on Earth, its atmosphere contained very little oxygen and therefore little ozone. Somehow, life on Earth got its start "without a protective atmosphere present," says Friedmann. By studying the organisms that live in the Licancabur summit lake, he hopes to find out something about how early life on Earth managed to cope with high UV. "The mechanism they use to survive in this environment may be very ancient."
Cabrol, who can be found poring over images of ancient Martian lakebeds when shes not busy climbing terrestrial volcanoes, sees important similarities between present-day conditions at Licancabur and conditions on early Mars.
Cabrol likens the harsh, isolated environment of Licancabur to what was perhaps the final era of Martian habitability. "High UV, low oxygen, low atmospheric pressure: These must be the conditions that were on Mars 3.5 billion years ago, when the atmosphere was not completely gone, when there was still a little bit there, when local ponds were still possible," says Cabrol.
As Mars became more and more inhospitable, Cabrol adds, life would have survived only in "very isolated ecoystems, basically seeing their world shrinking year after year after year," much as Licancaburs summit lake is believed to be slowly shrinking. Studying Licancabur, Cabrol hopes, will help scientists to understand how life behaves under such conditions and help to focus their search for evidence of ancient Martian life.
High-altitude Hydrothermals
Another area of interest is how the lake maintains itself. No-one knows what water source feeds its lake. Annual precipitation is only a few centimeters per year. For most of the year, the lake is frozen over; even when it thaws, its water temperature never warms to more than a few degrees above 0 C (32 F).
One theory is that there is an underground hydrothermal system feeding the lake. Although Licancabur itself is dormant, the region surrounding it contains a number of active volcanoes. Its possible that there is a source of heat, water or both lying beneath the volcano. Another possibility is that the ice that covers the lake most of the year provides a greenhouse effect, warming the water below.
Its also unclear how life got into the lake in the first place. If there is a hydrothermal system beneath the lake, organisms could have migrated up from lower altitudes. Or airborne microorganisms might have been carried there by the wind, although this is considered unlikely because of the lakes extreme isolation. Perhaps humans either the Incas in the distant past, or recreational mountain climbers more recently - introduced life to the lake. By whatever means the life forms got there, though, they could not have survived for long without evolving a means to minimize the effects of UV.
A Stop Along the Way
On their journey to Licancaburs summit, the researchers will make several stops. One of these will be at a refuge, at 4100 m (13,450 feet) above sea level. The refuge is a downscale version of a hostel, where travelers to the Andean wilderness can find a bed and a hot meal. Migrating flamingos, as well as humans, are frequent visitors there.
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