Reply to post: Re: Suggestive, but nothing more

NASA finds more stuff suggesting Mars could have hosted life, maybe

handleoclast Silver badge

Re: Suggestive, but nothing more

@boltar

1) A planet with an enviroment for suitable chemical reactions to occur

2) Somehow the chemical reactions lead to a self reproducing system

There are over 100,000,000,000 galaxies, each of which has an average of 100,000,000,000 stars (those are old figures, the newer ones are bigger but the old ones are easy to remember). Life has to be astronomically improbable not to occur more than once in this universe.

As it happens, life on this planet happened within around 300,000,000 years of it cooling enough for life to survive. Maybe we were much faster than average, maybe much slower, but the chances are we were somewhere in the middle. The odds look good.

3) Single celled life became multicell

That may be the hard step. It required (for our form of life, that may not be universally true) the formation of the eukaryotic cell by the symbiosis of two bacteria (one became the dominant partner, the other became mitochondria or chloroplasts, depending whether animal or plant). Then again, we have other examples of symbioses like these forming, mainly in protozoa which have cilia that are bacteria. So maybe not so hard.

4) Life had to make it out of water onto land (not much chance of fish building a spaceship) which was possibly helped by a large moon causing tides

Electronics would be hard. Try making vacuum tubes (valves) or zone-refining semiconductors underwater.

However, our tides have two components: one from the moon and one from the sun. When they act together the result is a larger "spring tide." The sun alone would still produce tides.

In any case, tides would result in life ending up in rock pools that either evaporate long before any evolution could happen, or are swept back out to sea by a later tide. Not much opportunity to get to a land form there. Large rivers, however, produce a salinity gradient at their mouths, allowing a transition from salt water to fresh water. From there, a transition to land may be easier.

So probably not a major problem either.

5) Humans had to evolve - not a given especially if that asteroid had missed 65 million years ago

Intelligent life has to evolve. That, again, seems hard. Then again, both elephants and whales are pretty intelligent. As are chimps. So without that asteroid maybe we'd have ended up with intelligent dinosaurs. Or not.

6) The industrial revolution had to occur. Again not a given - if there had been no coal deposits we'd still be riding around on horses with the most advanced machines being windmills.

Probably true. Although the limiting factor would probably be refining metal ores without coal or oil.

7) The computer revolution had to occur.

We had radio before we had computers. We were pumping out detectable signals without computers. Los Alamos managed to design the atomic bomb with nothing more than a lot of people and mechanical calculators, so I think we could have managed to calculate enough to get to the moon without computers (if we really wanted to).

I'm sure there are plenty of other important points in history that could have led to a very different outcome, but the point is - life evolving may or may not be rare, but a technological civilisation IMO is.

Yes, technological civilizations are going to be rarer than single-celled life. More importantly, those civilizations would have to arise within a narrow time/distance window for us to spot them by radio. And it's possible advanced technological civilizations don't survive long after developing nuclear weapons.

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