Does a Clam Know it’s Alive?

The late Carl Sagan guessed there might be 1 million civilizations in our galaxy, the Milky Way.  He based this guess on the Drake Equation–a formula that takes the number of stars in the galaxy and multiplies it by fractions of: sun-like stars, sun-like stars with planets, planets in inhabitable zones, planets where life evolved, planets with intelligent beings, and the percentage in the lifetime of a planet with a civilization.  However, the Rare Earth Hypothesis proposed by Peter Ward and Don Lee in 2000 posits microbial life may be widespread in the universe, but complex life must be extremely rare.  Since the Rare Earth Hypothesis was proposed, astronomers have discovered 3600 exoplanets in solar systems outside our own.  The evidence so far indicates the Rare Earth Hypothesis might be the more accurate guess.  Of the 3600 exoplanets discovered just 1 is a rocky earth-like planet that orbits in an inhabitable zone.  It is known as Proxima b. All other planets found in habitable zones are gas giants with no surface, similar to Jupiter and Saturn.  Though Proxima b is located in an habitable zone, it probably does not support life because it is tidally locked, meaning 1 side of the planet always faces its sun.  Half of the planet is too hot, and the other half is too cold.

Complex life evolved on earth thanks to numerous unique characteristics that apparently are extremely rare elsewhere in the galaxy and probably the universe.  Earth is just the right distance from the sun, and the sun is just the right kind of star.  Our sun is bigger than 95% of other stars.  The habitable zones of planets orbiting smaller stars would have to be much closer, but this would make the planets tidally locked like Proxima b or Mercury.  Moreover, most other solar systems are binary.  Solar systems with 2 or more suns force planets to have wild perturbations in their orbits, causing a great frequency of cosmic impacts that extinguish complex life.  Earth is the only known planet with abundant tectonic activity which helps control CO2 buildup.  Without tectonic activity CO2 concentrations in the atmosphere amplify heat and scorch complex life into extinction.  Venus is an example of this kind of uninhabitable world.  And earth is lucky to have a large moon that stabilizes earth’s tilt.  The earth’s tilt varies between 23.5-25 degrees, but planets without a large moon may vary in their tilt by up to 90 degrees.  The resulting climate instability would cause the complete extinction of complex life.

Microbial life first evolved on earth about 4 billion years ago, but complex plants and animals don’t appear in the fossil record until about 700 million years ago–a colossal gap in time.  Most earth-like planets in the universe probably resemble the early earth of 2.5 billion years ago.  The earth of that time was mostly ocean with a few volcanic islands.  The ocean was brown from cosmic-impacted debris, and the sky was red in an atmosphere of little free oxygen.  Eventually, plate tectonics formed continents, and shallow water environments supported greater populations of photo-synthesizing bacteria that produced enough oxygen to support complex life.

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Illustration of early earth’s atmosphere.  Land was restricted to a few volcanic islands and the sky was red in an atmosphere with little free oxygen.

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Early microbial life on earth resembled these primitive thermophilic Archaea.  They can survive in temperatures exceeding the boiling point.  This suggests microbial life may be widespread in the galaxy, though complex life is much more rare.  It took over 3 billion years for microbial life to evolve into complex life on earth.

Though complex life must be rare, there are between 1-2 billion galaxies in the universe, each with up to 1 billion stars that in turn have close to 10 planets in their systems.  The universe is so vast complex life likely evolved elsewhere besides earth.  But why?

I think the universe would not exist without complex life aware of its existence.  Suppose complex life never evolved anywhere.  Sure, there could be billions of galaxies, but if there was nothing aware of all that matter, it might as well not exist.  No sentient being would know it was there, so it would not be there.  This is why I think the universe produces worlds where complex life evolved.  It is an attempt by the universe to exist.  It becomes self aware through the minds of many individual sentient beings.  This complex life can’t be just a tree or a clam or a thermophilic micro-organism.  I doubt those living things are aware of their own existence let alone the existence of the universe.  Dogs and cats are aware of their existence, but I doubt they contemplate the existence of the universe.  Give them a smelly piece of meat and a caress and that’s as far as their in depth thought of the universe goes.  I believe the universe strives to produce life that recognizes it exists.  Otherwise, it will cease to exist or it may as well not exist because no sentient being would know of its existence.  Without complex life equivalent or above the intelligence of humans, the universe would have no knowledge of its existence, so it would not exist.

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I doubt a clam knows it is alive.  I believe the universe depends on life more complex than this for its existence.  The existence of complex life and the universe is an interdependent relationship.


Ward, Peter; and Donald Brownlee

Rare Earth: Why Complex Life is Uncommon in the Universe

Copernicus 2000


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3 Responses to “Does a Clam Know it’s Alive?”

  1. m Says:

    Sounds like a chicken egg thingie?? The universe was here before us.

  2. markgelbart Says:

    But if intelligent life didn’t evolve, it wouldn’t exist.

  3. m Says:

    Debatable but interesting.

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