Date: Wed, 01 May 2002
Blue Planet: Seas of Life
Thomas M. Miovas, Jr.
I've been watching the new Discovery Channel series "Blue Planet -- Seas of
Life" with some fascination. Recent discoveries presented in the series
shows the amazing resilience of life on earth (and by extension the
possibility of life on other planets).
Prior to the 1970's expeditions to the bottom of the ocean (the
mid-Atlantic ridge), it was thought that all life on earth was dependent
upon the sun, for photosynthesis. The idea was that the more complex
animals feed off lower life forms, and that the bottom of the food chain
were plants, which got their energy needed for living directly from the sun.
Bacteria were also believed to be dependent upon photosynthesis, because
the bacteria needed something to eat, and there wouldn't be anything for
them to eat if it wasn't for photosynthesis.
Discoveries made at the bottom of the ocean indicate there are two entirely
independent ecosystems that thrive without sunlight. One thrives because
the bacteria in the area get their energy by chemically fixing hydrogen
sulfide solution gushing up from black smoker vents; the other thrives
because bacteria in the area get their energy by chemically fixing methane
gas oozing from the mud. Prior to these discoveries, it was thought that
both hydrogen sulfide and methane were deadly to almost all forms of life
on earth.
In both ecosystems, higher forms of life -- including tube worms and
muscles -- have a symbiotic relationship with these bacteria, which live in
their tissues and provide them with the energy necessary to live their
lives, while the higher forms of life provide certain other gases extracted
from the ocean water more efficiently than the bacteria can do on their
own. The higher forms of life in these ecosystems do not eat -- they have
no stomach and no digestive system -- so they are directly dependent upon
the bacteria, which can survive on their own. [How the higher forms of life
develop their body tissues without eating anything is a mystery that wasn't
explored. I mean, they would have to incorporate raw materials somehow.]
With these two discoveries, it's no longer a puzzle as to how life began on
earth when the early atmosphere of earth was so thick with the gases of
methane and hydrogen sulfide that no sunlight could reach the surface:
photosynthesis wasn't needed! There was enough hydrogen sulfide and
methane covering the entire planet for bacteria to thrive.
As these chemicals were used up by the bacteria, the atmosphere slowly
became transparent, leading to the evolutionary track of photosynthesis.
While this series made no projections of the possibility of life on other
planets, it is interesting to note that our solar system has several gas
giant planets -- with atmospheres comprising primarily of methane and
hydrogen sulfide, along with many amino acids thought to be necessary for
the building blocks of life.
