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When a barren planet is in the process
of being terraformed, there will come a point where the first life
forms can be introduced into the natural environment.
The implantation of this pioneering
biosphere is often referred to as ecopoiesis. Initially, and perhaps
well before plants and animals can be introduced, such a world is
going to be suitable only for bacteria hardened to environmental
extremes - the so called extremophiles. Here, we review some of the
ecopoiesis candidates nominated by various authors.
It's possible that one of the
microscopic creatures described below could be the first terrestrial
life form to truly colonize an alien world.
Mars
Ecopoiesis is conventionally regarded as being possible on Mars once
its CO2 atmosphere has been thickened and its greenhouse
effect increased such as to raise the surface temperature above
freezing.
Mars would thus be tepid rather than
frozen, but still relatively dry and anaerobic. (It is expected that
generating breathable quantities of oxygen and mobilizing the
planet's reserves of water will take still further time and effort.)
Here are some of Earth's extremophiles
that might prosper under such conditions.
Chroococcidiopsis sp
A primitive type of cyanobacterium,
capable of surviving in a large variety of extreme conditions:
exceptional aridity, salinity, high and low temperature. In the
most hostile of these environments, Chroococcidiopsis can be the
sole surviving organism.
It is particularly common in regions
with desert pavement morphology, living beneath translucent
pebbles which act both as a moisture trap and UV shield.
E.I. Friedmann, and R.
Ocampo-Friedmann, "A Primitive Cyanobacterium as Pioneer
Microorganism for Terraforming Mars," Adv. Space Res., 15(3),
243-246 (1995).
Matteia sp
The only known desiccation-resistant
cyanobacterium that can dissolve and bore through carbonate
rock.
Matteia is filamentous in shape and
has the ability to fix nitrogen when nitrogen compounds are
unavailable from the surrounding medium. It has been suggested
that this organism might be used to liberate carbon dioxide on
Mars and as part of a biogeochemical carbon cycle.
E.I. Friedmann, M. Hua,
and R. Ocampo-Friedmann, "Terraforming Mars: Dissolution of
Carbonate Rocks by Cyanobacteria," JBIS, 46, 291-292, (1993).
Deinococcus radiodurans
A heterotrophic bacterium with
impressive resistance to UV and ionizing radiation, due to a
multilayered cell wall, carotenoid pigments and super-efficient
DNA repair mechanisms.
D. radiodurans is sometimes found
living in the cooling waters of nuclear reactors.
Genetic study of this organism might
reveal how to protect future Martian life forms from solar
ultraviolet radiation, before an effective ozone layer is in
place.
J.A. Hiscox and D.J.
Thomas, "Genetic Modification and Selection of Microorganisms
for Growth on Mars," JBIS, 48, 419-426 (1995).
Venus
There are a variety of scenarios for terraforming Venus, all with
their merits and flaws. In some of these, ecopoiesis could occur on
Venus in scalding hot and acidic oceans, precipitating from a global
"Big Rain" as the planet cools.
Due to the steep thermal gradient in the
crust, hydrothermal activity would be strong and ubiquitous - hot
springs would be everywhere.
Pyrodictium occultum
A hyperthermophilic bacterium with a
metabolic optimum of 105 celsius, P. occultum is found living
within submarine volcanic vents where it attaches itself to
underlying rocks with a network of proteinaceous fibres.
It is lithoautotrophic, obtaining
energy by oxidising hydrogen with sulphur, and gaining biomass
by fixing carbon dioxide. Venus after the "Big Rain" would be
paradise for such an organism.
M.J. Fogg, Terraforming:
Engineering Planetary Environments, SAE International,
Warrendale, PA (1995).
Halobacterium salinarum
According to the model of Stephen
Gillett, oceans on a terraformed Venus are likely to be shallow
and hypersaline and hence more similar in composition to the
Great Salt Lake or the Dead Sea than the oceans of earth.
H. salinarum is one organism that
might thrive under such conditions: it can live in concentrated
salt solution and, although heterotrophic, pigments in its cell
wall can absorb light energy to augment its metabolism.
S.L. Gillett, "The
Postdiluvian World," Analog, CV(11), 40-58 (1985).
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