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Old 02-01-2017, 02:47 PM
Mark Johnston Mark Johnston is offline
PAS Member
Join Date: Dec 2015
Location: Scottsdale AZ
Posts: 6

Here's my view:
First of all, we have only direct access to one world with water, so clearly with a sample size of 1 it's hard to extrapolate. But I believe the likelihood is high that simple life will arise (has arisen) on 'wet' worlds.
I would cite the Miller experiment, first performed in 1952, where the gases present in Earth's early pre-life atmosphere were mixed together with water, sparks added (to simulate electrical discharge of lightning) and dozens of amino acids, fatty acids and urea were spontaneously created. This experiment has been repeated dozens of times with the same results. These molecules and sugars are also routinely found in meteorites, which suggests they form naturally and easily.
Further tests have shown that given time, when such organic molecules are left alone with an energy source, they begin to link together to form more complex structures. Certain molecules can self assemble into orderly structures - hollow spheres similar to the membranes of cells, and long chains that are suggestive in structure to DNA. (look up "chemical evolution")
In 2016 fossils were found in Greenland that were 3.7B years old, suggesting life arose immediately on Earth as soon as it was formed and the heavy bombardment phase was over.
Neil de Grasse Tyson has an excellent video on how the eye evolved from a crude mass of cells that could not differentiate bright from dark to the complex and elegant structures that are now common.
I would be willing to bet we'll find evidence of microbial life in our own solar system (e.g. Europa) or detect molecular oxygen in an exoplanet's atmosphere (indicating life) within 20 years. Sadly, I doubt we'll spot alien space ships, or even fat creatures doing the backstroke in Titan's seas, but do think simple life is common and will soon be discovered.
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