West Lafayette, IN (02/09/04)- The
question of whether there has ever been life on Mars is still not answered,
but the
fact
some
microbial organisms on Earth thrive in highly inhospitable conditions is
one of the things that spurs on the search for life on other planets. These
organisms, which for the most part are either bacteria, or bacteria-like,
are commonly referred to as extremophiles because of the extreme conditions
in which they thrive.
Take
Deinococcus radiodurans
as an example. This bacterium is found in soil but can survive exposure to
3 million rads (100
rads equals 1 Gray) of ionizing radiation. It is able to repair chromosomal
damage caused by heat, dehydration and radiation within 12 to 24 hours,
which contributes to its survival.
In contrast, humans are killed by exposure to less than 500 rads. With organisms
like this on Earth thriving in these sorts of levels one wonders whether
equally tolerant organisms elsewhere, such as Mars.
Bacterial
mat grows at underwater vent, 160C. NOAA
“What Mars is like seems pretty bizarre to us humans. The conditions
there, temperature, atmosphere and more, are very different from what we
have here on Earth. On the other hand, we know there are places on Earth
that are quite far from normal yet life thrives there,” said Allan
Konopka, PhD, Professor and Interim Head of the department of biological
sciences at Purdue University.
Thermotoga is
an Archaea
organism, which is bacteria-like, and is another example of a so-called
extremophile. It has adapted to conditions in hot springs
and hydrothermal vents, thriving at temperatures up to 90C. As well, there
are mats of bacterial organisms that live in 160C temperatures around hydrothermal
vents
more than 1000m beneath the ocean surface. The organisms were discovered in
1999 by researchers from the National Oceanic and Atmospheric Administration
(NOAA)
at an underwater volcano site near Hawaii.
Methanopyrus
another Archaea organism that lives near submarine hydrothermal
vents and grows in temperatures as high as 110C. Interestingly, it gains
energy
from hydrogen gas and makes methane gas as a metabolic end-product. One thing
extremophile life-forms on Earth have in common is a need for liquid water, and
this is why there has been such a stir about the existence of frozen water on
Mars. If, at any point in the planet’s long history there had been water
in a fluid state, the chances there may have been living organisms at some
time increase.
"Even though the conditions on Mars seem so inhospitable to us that
doesn’t
preclude the idea there were microbes there at some point that were able to
grow there," Dr. Konopka said.
Yet life on Earth demonstrates that organisms can live in water that
is very hot, or very cold, as long as it is in a liquid state. “As
long as water isn’t boiling, there are microbes growing,” he
said. But the temperature of boiling water
differs, according to elevation and pressure. At deep-sea hot vents, far
higher temperatures are required to make water boil
than it would at sea level or other higher elevations. Indeed, there are microbes
living in the Yellowstone hot springs, but because of the high elevation there
water comes to a boil at only 80C to 90C, not 100C.
"Hydrothermal vents on the bottom of the ocean are interesting, because
of all the hydrostatic pressure of a thousand meters of water above it. There,
water
doesn’t boil at 100C, but at 150C. Yet at those temperatures bacteria
are growing and active," Dr. Konopka said. Some vents have water that
is as high as 300C, but so far microbes have been found at temperatures no
higher than
160C.
Dr. Konopka points out that the Dead Sea isn’t so dead either.
Both the Dead Sea and Great Salt Lake have thriving communities of microscopic
salt-loving
life called Halobacteria.
The bacteria typically live in water with extremely high salt concentrations
of 4 to 5 M NaCl. The high salt concentrations are needed for the stability
of the organisms' membrane and they will die in seawater,
which is too dilute. Yet other organisms prefer conditions of either low
or high
pH,
and can’t
survive in a neutral environment.
There are also organisms that prefer cold temperatures, such as Polaromonas
vacuolata
which live in the ice in the Antarctica at temperatures that are either at,
or
just below, freezing. Organisms such as this, and Deinococcus radiodurans are inspiring researchers at NASA’s Astrobiology Institute to speculate
there may once have been microbial life not only on Mars, but possibly on
icy Europa,
one of Jupiter’s moons.
In a universe with an estimated ten-billion trillion stars, along with
all their orbiting planets, odds are life of some sort exists elsewhere.
end
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