What's Living in the World's Highest Lake?
The atmospheric pressure at Licancabur's summit is less than half that at sea level. Because of this thin atmosphere and the volcano's low latitude - Licancabur is only 2500 km (about 1500 mi) south of the equator - the summit is exposed to more intense ultraviolet (UV) radiation than just about any other spot on Earth.
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 volcano's 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.
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 wouldn't 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.
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 NASA's 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
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 she's 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 Licancabur's 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.
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 oC (32 oF).
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. It's 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.
A Stop Along the Way
On their journey to Licancabur's 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.
The refuge lies near a group of three alpine lakes that are also of interest to the scientists. The two larger lakes are Laguna Blanca and Laguna Verde. "And there is this small pool in between the two that is heated," explains Cabrol. "So my theory - and you just look around and you see the paleo [ancient] shoreline - is that this was one lake tens of thousands of years ago during the end of the last glacial age." All three lakes, she speculates, may have been part of a single hydrothermal system. "Now they have been separated by evaporation, but who knows?" Cabrol wonders. "There might be other heat sources in the larger lakes."
The scientists will spend just over a week at the refuge, acclimatizing themselves to the high altitude. But while there, they will also perform many of the experiments in the nearby lakes that they will be performing in the summit lake.
A Link to the Past
Licancabur was a sacred mountain to the Incas. Incan ruins have been found near its summit. "Licancabur, was used by the Incas to communicate between mountains. The Inca would climb up there and set fires" to send messages.
Cabrol sees a link between her expedition and the mountain's historic use. "The Incas were going there to try to communicate and understand better the secrets of nature and whatever god of nature was there, and to understand their place in the universe and the cosmos. And we are doing exactly the same."
Of course, her team will communicate its findings by satellite phone and the Internet, rather than by fire. Still, says Cabrol, "I find it neat to think about it."
This is the first in a series of four articles about the Licancabur expedition. Each Monday for the next three weeks, we will bring you interviews with different scientists who are participating in the expedition.