MadSci Network: Earth Science

Re: Astronomy

Area: Earth Science
Posted By: Sean Sherlock, Grad student Geology
Date: Sun Aug 18 22:59:50 1996
Message ID: 839089820.Es

What would the Earth be like, physically and biologically, if it had one or
two small moons instead of one large one?  A very interesting question.

Physically, the appearance of the Earth would probably not be much
different.  The greatest difference would be in the ocean tides.  Since the
moon or moons would have less mass than our actual Moon, there would be a
smaller range between the elevations of high and low tides (assuming that
the moon or moons are at a distance from the Earth similar to the real
Moon).  The orbital distance of the moons would also be a factor in the
strength of their gravitational attraction, which causes tidal forces.  The
timing of the tides would also be different, and much more complex, if there
were two moons.  Tidal forces act in the Earth's crust as well as in the
oceans.  Some have suggested that these tidal forces may have a role in
triggering earthquakes and other phenomena.  The effects of Earth tides on
geologic processes are not well understood, but their overall influence is
probably minor in comparison to tectonic forces.  The difference in tidal
range would probably have an influence on the sedimentary rock record as

Biologically, the effects would be much greater.  Tidal ecosystems would be
drastically affected.  Any animals whose mating behavior is linked to the
lunar cycle (such as the human menstrual cycle) would be affected.  There
would probably be some effect on the behavior of nocturnal creatures in
general.  Exactly what the differences would be is difficult to guess, but
it would likely alter the course of evolution of many species.

In addition, it is possible that the Moon may have intercepted or
gravitationally deflected some small percentage of asteroids and comets that
otherwise would have hit the Earth.  Having a moon of lower mass might
result in a slightly greater number of impacts on the Earth over the course
of geologic time.  Since these impacts are suspected as causes of mass
extinctions, a change in their frequency and timing could have had a
drastic influence on the evolution of all life on Earth.

There really is no precise answer to your question, since the results of an
alternative evolutionary path are impossible to predict.  It might be fun to
speculate, however.  Good luck.

----  Sean Sherlock

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