The moon might have played a role in the crucial ocean-to-land evolutionary leap.
Ask Dr. Knowledge
Life presumably started in the oceans, and at a certain point in time it evolved onto dry land. The transition from ocean-based life to land-based life must have been greatly aided by the twice-a-day tides. The bigger the tides the more slopping around of water at the land-ocean boundary and the higher the probability of evolution from ocean life to land life since some initially water-dwelling things will simply find themselves on land when the tide goes out.
On Earth we have two objects responsible for the tides; these are the moon and the sun. Today the moon has a bit more than twice the effect of the sun. A long time ago, when the moon was significantly closer to Earth, the tidal effect of the moon would have swamped that of the sun.
Without tides, it would probably be quite unlikely for life to advance out of the oceans, and it is unclear just how advanced ocean-based life can become. Perhaps fish would represent the most advanced life form (ocean mammals such as dolphins evolved partly on land and returned to the sea). On the other hand, even without the moon, our solar tides would be quite significant and perhaps large enough to aid in the crucial ocean-to-land evolutionary leap.
The real test will come when we study what happened on the planet Mars. Mars has tiny insignificant moons and the solar tidal effects are about 15 percent of those on Earth. There is a growing body of evidence to suggest that Mars once had significant ocean coverage and surely life would have started in those oceans. If that turns out to be true it will be fascinating to see just how advanced it became.
Dr. Knowledge is written by physicists Stephen Reucroft and John Swain, both of Northeastern University. E-mail questions to drknowledge@globe.com or write Dr. Knowledge, c/o The Boston Globe, PO Box 55819, Boston, MA 02205-5819.
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