Extremophiles And Now Shrimps Boosting The potential For Life On Other Planets
May 6, 2010 11 Comments
When considering the presence of life under adversity, we shouldn’t be too quick to rule out environments based solely on extreme properties. The underwater hydrothermal vents are very hostile places as judged by life on or near Earth’s surface, yet life manages to thrive around them under conditions quite unlike anything at the surface. Undersea volcanic activity spills forth scalding-hot water rich in sulfur and poor in oxygen that manages to feed “extremeophilic” life by a process known as chemosynthesis—an analog of photosynthesis, yet one that operates in total darkness. Here, teeming colonies of organisms survive and prosper at temperatures close to, and sometimes even exceeding, the usual boiling point of water on a diet of H, CO2, and elemental sulfur (S), while exhaling toxic (to surface creatures) hydrogen sulfide (H2S). A variety of deep-sea animals resembling clams and worms form symbiotic partnerships with bacteria that get their energy from sulfides rather than light. Despite the decidedly odd conditions and even odder metabolisms, all known extremophiles inhabiting vent environments are still based on the element carbon, just like the rest of us living in the more traditional biosphere in or around Earth’s surface.
The volcanically heated springs of Yellowstone National Park are another good example of an exotic site where a wealth of life flourishes under extreme conditions inhospitable by human standards. There, the rich microbial diversity hardly includes garden-variety types, yet, surprisingly, many of the microorganisms’ genes approximate many of ours. At the molecular level, these hot little creatures resemble eukaryotes more than bacteria, in fact they differ from conventional bacteria more than do humans from a crab. Though in the public eye microbes are often seen in the context of disease and rot, these heat-loving bugs might be telling us something important about how the earliest life forms employed inorganic nutrition (in the absence of carbon) and geothermal heat (without the Sun’s radiation). Carbon-centered metabolism and solar-driven photosynthesis arose comparatively later.
Underground hot springs and the extremophilic life thriving near them raise the possibility of life forms with even greater diversity amid even wilder conditions than those known to us on Earth. This is especially true if we broaden our perspective yet more to consider life at the other extreme—cold. Household refrigerators (or at least their freezers) surely retard the growth of bacteria—that’s the job of those machines—but life can sometimes still eek out a living there. In fact, the bottoms of perennially frozen lakes in Antarctica harbor entire communities of microbes, despite temperatures nearly equaling the freezing point of water. These aren’t merely bacteria, but also microscopic plants and animals. In a few places, microbial life holds on and avoids death even within the thick, hardened ice itself, surviving in a kind of suspended animation, apparently indefinitely. The frigid, dry, Antarctic climate resembles that of Mars today, bolstering the idea that frozen tundra on the red planet could support life under Spartan conditions. Other inhospitable places on Earth where simple, yet active life has been found include subterranean rock, salt deposits, and even oil fields, all >1 km below Earth’s surface.
Discoveries during the past decade have brought much wider appreciation for life on our own planet, revealing bacteria in places where biologists once thought nothing could possibly live. Adaptation is the key, as so often the case, and the simplest forms of life seem to be surprisingly adaptive to all sorts of environmental extremes. Marine microbes alone, living in the unpromising milieu of seafloor sediment, are now thought to comprise nearly 1/3 of all living organisms on Earth, yet very little is known about them. Perhaps fully half of Earth’s total biomass is made of microbes, many of them extending as much 1 km into the crust. This is a whole new “deep biosphere” that geologists are only now beginning to explore by underwater drilling. Even in the more accessible (upper) parts of the ocean, bacteria are known to be much more numerous and diverse than previously thought—roughly several billion microbes infuse every teaspoon of water. All told, the oceans are brimming with an estimated 1027 bacteria, or roughly a million times more cells in the sea than stars in the visible Universe. And if many of these microbial life forms within and under the sea are sucking up carbon, they may collectively comprise a huge sink that absorbs carbon pollution produced by today’s civilization and thus mediates climate warming on a global scale. How many more species are yet to be found in the depths of this, the largest habitat on Earth? And if life is so robust in unlikely places on Earth, to what extent does that raise the prospects for extraterrestrial life, even if it’s only simple, creepy-crawly life?
Consider two candidates for alien life: Jupiter’s moon Europa has a metallic core, rocky mantle, and probably more water locked in and beneath ice near its surface than in all the seas on Earth. Though the evidence for water is only conjectural, its likelihood opens up many interesting avenues for speculation about life. The Galileo mission to Jupiter recently returned direct imagery showing Europa totally ice-bound, yet those pictures also show a smooth yet tangled surface resembling the huge ice flows that cover Earth’s polar regions. Something, most probably the tidal effects of Jupiter, is causing this moon (which is comparable in size to our own Moon) to be active and thus to allow water to be energized independent of the Sun. But a caveat is in order: Where there’s water doesn’t necessarily mean there’s life.
Likewise, Saturn’s big moon Titan is a place where odd life forms, or at least the prebiological ingredients that comprise life, could be present. Titan has twice the mass of our Moon and an atmosphere thicker than Earth’s. Nearly 90% of Titan’s gas is nitrogen, much like Earth’s air, laced with hydrocarbons (which are molecules made solely of H and C, such as methane, CH4). Titan’s environment must resemble a gigantic biochemical factory powered by the energy of sunlight—and where there’s energy and organic matter, well, who knows? It’s mighty chilly there, though; direct measurements prove that Titan’s surface temperature is a frigid ~75 K (-200oC)—so cold that ordinary ice would be as hard as steel and even methane lakes frozen. If life forms do exist, or have existed, on alien worlds, they will probably be quite unlike those populating the sea ice on Earth today.
Life on Titan is even more Probable than ever
Microbial life has been found in Pitch Lake of asphalt. Pitch Lake is a poisonous, foul smelling, hell hole on the Caribbean island of Trinidad and Tobago. The lake is filled with hot asphalt and bubbling with noxious hydrocarbon gases and carbon dioxide. Water is scarce here and certainly below the levels normally thought of as a threshold for life. An active microbiota, reaching up to 10 E+7 cells/g, was found to inhabit a naturally occurring asphalt lake characterized by low water activity and elevated temperature. Geochemical and molecular taxonomic approaches revealed novel and deeply branching microbial assemblages mediating anaerobic hydrocarbon degradation, metal respiration and C1 utilization pathways. These results open a window into the origin and adaptive evolution of microbial life within recalcitrant hydrocarbon matrices, and establish the site as a useful analog for the liquid hydrocarbon environments on Saturn’s moon Titan.
These alien conditions have made Pitch Lake a place of more than passing interest to astrobiologists. Various scientists have suggested that it is the closest thing on Earth to the kind of hydrocarbon lakes that we can see on Saturn’s moon Titan. Naturally, these scientists would very much like to answer the question of what kind of life these places can support.[Download PDF version of research paper]
Here I would also like to mention new extremophile found lurking 600 feet beneath ice. as you can see this critter is a three-inch long Lyssianasid amphipod found beneath the Ross Ice Shelf, about 12.5 miles away from open water.
NASA scientists were using a borehole camera to look back up towards the ice surface when they spotted this pinkish-orange creature swimming beneath the ice. Though we have found other extrmophiles under very harsh conditions but they were only microbes, single cell creatures, but this discovery has given a new leap to the definition of life. Of course this is a multi-cellular creature. Watch this video
[ref:arxiv.org/abs/1004.2047: Microbial Life in a Liquid Asphalt Desert]