Life in the Universe
I. Requirements to be considered Life
-- must have cell structure and metabolize energy, responding to
and interacting with its
environment in some way
-- must die, so must first be able to reproduce, using a genetic code.
The code in effects "saves" the information that we have a viable
organism that can survive in its environment, and modifications to the
code from generation to generation causes gradual changes in the organism.
Natural selection then culls out the ones that survive best, causing a kind
of environmentally guided natural process called "evolution".
II. Environmental Needs
-- a heat source, typically either the Sun or geothermal heating in deep
ocean vents
-- a way to metabolize energy and carry out the other necessary chemical
processes, and the only molecules known to have the required complexity
are "organic" molecules that contain carbon
-- water in the liquid phase, which is the most difficult to find in the
solar system, because it requires a significant pressure combined with
medium temperature
III. Possible locations
-- Mars may have had oceans in the past, requiring it to have a thick atmosphere and a significant greenhouse effect. That could have made it conducive
to life on the surface
-- Europa and Enceladus are moons of gas giants that have geothermal
heating due to tidal friction caused by the planets they orbit. Below the iice there may be liquid water, and deep ocean vents as on Earth.
IV. Intelligent life
-- the "Drake equation", estimates the likelihood of our galaxy containing other
intelligent life we might receive a communication from (SETI)
-- the major uncertainly is how long an intelligent species can survive.
Is intelligence enough of an advantage to help such a species survive
even longer than the roughly 50 million years most animal often species get,
or it is a disadvantage to "know too much" that limits the species to a few thousand years after becoming intelligent?