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Methane-Based Life Possible On Titan
Randym writes: With the simultaneous announcement of a possible nitrogen-based, cell-like structure allowing life outside the "liquid water zone" (but within a methane atmosphere) announced by researchers at Cornell (academic paper) and the mystery of fluctuating methane levels on Mars raising the possibility of methane-respiring life, there now exists the possibility of a whole new branch of the tree of life that does not rely on either carbon or oxygen for respiration. We may find evidence of such life here on Earth down in the mantle where "traditional" life cannot survive, but where bacteria has evolved to live off hydrocarbons like methane and benzene.
Slashdot summaries are confused, when not outright inaccurate - news at 11. If you actually want to know details, you're pretty much required to RTFA.
As for your question, humans (/mammals/animals/multicellular organisms) are a recent addition, not typical of Earth-based life.
Earth life is water-based (well, suspended anyway), with lipid(hydrocarbon)-based cell walls to keep vital chemistry sufficiently concentrated to continue. Eventually blue-green algae evolved their ability to photosynthesize and poisoned the planet with toxic oxygen byproducts, which some of the survivors later managed to harness as a fuel. But that's really an incidental development so far as life itself is concerned. Before that life was all chemovores - likely consuming complex organic molecules from either hydrothermal vents and/or their fellows for both nutrients and energy.
In this case researchers have found some other hydrocarbons that can form "cell walls" with properties very similar to those in our own cells, except that they operate in a liquid methane suspension instead of water, at temperatures that would render our own cell walls solid. One of those hydrocarbons is acrylonitrile, a compound found in Titan's atmosphere, so the building blocks for cell walls at least are already present there.
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