Sunday, May 1, 2016

Eukaryotes and the Drake Equation

I bet a lot of the people reading this blog have heard of the Drake Equation but, as a recap, the idea is that given some assumptions you should be able to calculate how many alien civilizations there ought to be in the Milky Way.  There are a few problem with the way the equation is put together but in general it's hard make make assumptions strict enough that the galaxy shouldn't have lots of other civilizations.  And now that it's looking like most stars have planets that leads to the scary conclusion that maybe civilizations just don't last very long.

But thankfully I read a book recently that makes me a bit more hopeful.  A while ago I read Power, Sex, Suicide: Mitochondria and the Meaning of Life by Nick Lane which I really ought to have reviewed here because it was an excellent book.  It discusses how mitochondria allowed eukaryotic cells to become much larger than their forebears, the roll they plan in apoptosis or cell suicide, and how they effect how long various animals live.  But the important park in this blog post is how they were first created with one cell swallowing another and the two forming a symbiosis.

Without going into details (they're in the book!) it was sort of crazy that something like that could happen and result in a creature that was fit enough to survive.  I was recently looking at the timeline of life on Earth on Wikipedia and you can see that there.  The first simple cells appeared 4.1 billion years ago, just 400 million years after Earth got it's seas.  But it wasn't until 1.9 billion years ago, 2.2 billion years after life first appeared that we got eukaryotic cells.  So it looks like it took over 5 times as long for for complex cells to arise as it did for cells to in the first place.

If it had taken twice as long for simple cells to get going and the whole timeline of life on Earth was pushed back a half billion years then that wouldn't have been a big deal.  But if eukaryotes had taken twice as long to get going then the extra 2 billion years would push the arrival of complex life like us out to 6.5 billion years after the Earth formed by which point the sun will be hotter and there won't be liquid water on the surface any more.

So judging just by Earth's timeline we might go out into the wider universe to find that there are lots of bacteria out there but nothing big and complex enough to need a nucleus.  But of course all of this is still the thinnest speculation until we explore much more of the universe.

2 comments:

  1. The search for extraterrestrial intelligence stands upon some assumptions, I believe, which deserve scrutiny.

    The principal method of search, so far as I know, is for radio signals such as we transmit from radio stations. But we humans did not start emitting such signals until what, 100 years ago? And we might get smart enough to stop emitting such signals in another 50 years. So the people searching for intelligence are in fact looking for our peers, others in our present narrow band of stupidity.

    Another assumption is that we could recognize the intelligence of another set of life. But one of the lessons of cryptography is that a well encrypted signal looks like white noise to all who lack the key for decryption. So it could be that we just lack the key to see vastly greater intelligence in the white light all around us.

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  2. I agree that the lack of non-deliberate radio broadcasts doesn't mean much. But I would expect some fraction to be sending out deliberate radio signals or Bracewell probes if it were safe to do so. And I would expect some fraction to start expanding over the galaxy and showing up that way.

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