Geoscience Reference
In-Depth Information
The abundant life we find at the Guaymas Basin and many other deep-
ocean hydrothermal systems around the world is fueled by sulfide from
the vents, but critically, oxygen is also required. These sulide-oxidizing
bacteria live by combining the sulfide with oxygen. Take away the oxy-
gen, and what do we have left? The animals would disappear, the sulfide-
oxidizing bacteria couldn't survive, and indeed, almost every sign of life
that dominates our view through
Alvin
's portholes would be absent.
How about on a planetary scale? From the last chapter we saw that on
today's Earth, over 99% of the energy fueling the biosphere comes from
the Sun as channeled through oxygen-producing photosynthesizers.
Take away the oxygen producers and all of the food they produce, and
the great food chains of Earth would collapse leaving, well, what? This
question becomes relevant when we seek to understand the nature of
life on ancient Earth, before the evolution of oxygen production.
To answer this, we return to the Guaymas Basin (or nearly any other
spreading center with hydrothermal emissions). Take away oxygen, and
life would be greatly diminished, but there would still be some to find.
Let's think about what the hydrothermal fluids supply. As noted above,
in the oxygen-free depths of the oceans, sulfide would be of little use
to life, but hydrothermal fluids also contain lots of other compounds,
some of which are quite interesting to organisms. We start with hydro-
gen gas and CO
2
, both of which can reach quite high concentrations
in hydrothermal vent fluids. Remember the cows from the last chapter?
The same type of (autotrophic
5
) methanogens we find in their digestive
systems can also combine H
2
(hydrogen) and CO
2
to produce methane
in hydrothermal vent systems.
6
Indeed, many methanogens are adapted
to very high temperatures of over 100°C and are found associated with
modern hydrothermal vents.
Even without oxygen, these methanogens would grow and divide
and some would die. The population would reach a steady state of sorts,
where growth matched death, and the dead organisms would be food
for other microbes. Today, fermenting bacteria play a major role in the
decomposition of the organic compounds produced by organisms. They
gain energy and grow through the fermentation process whereby they
produce simple organic molecules that can be used by other microbes.
Indeed, methanogens of a different type (heterotrophic
7
) can use these
simple organic compounds and produce methane and CO
2
. Therefore,
