Geoscience Reference
In-Depth Information
hydrothermal ecosystems, which means water-containing terrestrial, subterranean, and
submarine high-temperature environments which are the sites of investigations for
many paleobiologists and biologists looking for primitive forms of life. It is strongly
believed that the roots of life on earth can be found in hydrothermal ecosystems.
These ecosystems may also serve as an analogue for the possible origin of life on
Mars, where a similar environment might have existed or still exist.
The conditions at the hydrothermal ecosystems mimic, to some extent, the con-
ditions on early earth because of the presence of both heat and water. These condi-
tions were abundant at around 3.5 Ga, when there was much greater vulcanism and
a higher ambient temperature on earth. Dick Henley
[86]
describes the geochemical
activity of the hydrothermal ecosystems as a biotic factory. According to Everett
Shock
[87]
, life thrives in submarine hydrothermal conditions because they have a
(geologically supplied) source of chemical disequilibrium which brings in redox
reactions. Further, he states that life originated at warmer temperatures. This was
also supported by simple experiments on organic synthesis under hydrothermal
conditions. These higher temperatures would mix various elements and supply the
energy for the formation of simple compounds. Abundant mineral deposits at
hydrothermal ecosystems imply that they provide a fossil record of their biological
inheritance. Often the minerals deposited are precious metals such as gold, silver,
copper, and zinc. These are common outpourings from hydrothermal vents.
Thermal waters usually contain high concentrations of dissolved components which
are deposited when the hot spring discharge gases are released and the temperatures
fall, leading to the deposition of mostly calcium carbonate, silica, iron oxides, and
manganese oxides. Thus, any living organism that once existed in the vents become
fossilized at the very site it lived in. All these theories proposed that the life existed
some 3.5 billion years ago.
The spectacular nature of the submarine hydrothermal ecosystem with features
such as black smokers, white smokers, and peculiar ecosystems, that are indepen-
dent of sunlight as a source of reducing power, has focused much interest on hydro-
thermal processes for the explanation of an array of geochemical processes and
phenomena
[88]
. The submarine hydrothermal systems reveal that most primitive
organisms found in modern environments are thermophiles (e.g., archea). Many
scientists believe in a “redox neutral” in the primitive atmosphere. The most impor-
tant aspect is the possibility that the iron vapor and reduced carbon liberated from
impacting objects like meteorites would leave the ocean, reducing for a long
period. In addition, those submarine hydrothermal systems are the only environ-
ments where primitive life would have been protected against postulated meteoritic
impacts and partial vaporization of the ocean. Supercritical fluids, like H
2
O, CO
2
,
or CH
4
, are the main constituents of any hydrothermal system. They serve as excel-
lent solvents of organic compounds and would probably be of great potential for
several of the chemical reactions eventually leading to the origin of life. Further,
the pressure and the temperature gradients existing in natural hydrothermal systems
have a dramatic effect on the properties of the hydrothermal fluids. This is known
from the current experimental data on many electrolytic solutions and some non-
aqueous solutions
[89]
.
