The Grand Prismatic thermal spring in Yellowstone National Park reaches around 87˚C but is teeming with microbes.
Credit: NPS Photo
SYDNEY: "We have an example of 'one'," says Jill Tarter, research director at the SETI Institute in California, referring to life on Earth.
"We cannot know from tracing the detailed history of that single experiment what the branching ratio might be for the experiment of life; how many other ways things might have gone but didn't, at what rate, with what result?"
But even on Earth, the boundary conditions for life have continued to be expanded over the past few years.
Pushing the boundaries
Scientists now think that there may be as much as 10 times as much biomass deep in the Earth's crust compared to the surface biomass, with which we are already familiar.
Life is no longer confined between the boiling and freezing points of water. The metabolism of an archean microbial Strain 121 still functions at 121˚C and at the other extreme, in Point Barrow, Alaska, the bacterium Psychromonas ingrahamii survives and reproduces at -12˚C.
Life is also no longer constrained to a neutral pH. The red alga Cyanidium caldarium and the green algae Dunaliella acidophila can live in the environments similar to that of the acid in a car battery, a pH level below 1.
Microbes have also been found thriving in environments more basic than ammonia, with a pH of 12.8.
Life in the dark
Sunlight, once argued to be the energy source for all live, is completely absent at the deep hydrothermal vents where a diverse community of organisms thrive.
But perhaps even more spectacular is Deinococcus radiodurans, which can withstand hard radiation because of its DNA repair mechanism.
When we think of the planets in our Solar System, in addition to the terrestrial planets Venus, Mars and Earth (which were all biologically connected during an earlier epoch of planet building and bombardment), we should consider the large icy satellites of Jupiter and Saturn, namely Europa, Ganymede, Callisto, and Enceladus where liquid, briny, water oceans are thought to exist beneath their icy outer crusts.
"All of these are intriguing possibilities. I would have been locked up in a looney bin when I was a graduate student if I'd even thought to mention this sort of thing," says Tarter.
Find out more in the latest issue of Cosmos magazine, with a 39-page special on SETI!
