The Earth and the Moon: A Match Made in the Heavens

The Moon’s a pretty darn awesome thing to have.  Look at all it gives us.  A way to track the days, the majesty of the tides, crackpot prognostication in the daily newspaper … and eclipses!  How cool are eclipses?!  Life would be a lot more boring if it weren’t for the Moon.  The thing that’s not immediately recognizable, though, is that life might not be at all if it weren’t for the Moon.

The Earth’s moon seems to have formed in a similar fashion as the satellites belonging to the other planets in our solar system, but with a key difference.  Recent studies suggest that moons form when material within ring systems, like Saturn’s, coalesce to form the rocky companions.  It’s thought that ring systems of the outer planets were comprised of leftover material from the accretion of each protoplanetary disk, but the debris that encircled the Earth and condensed to create our Moon probably had a different source.  Namely Theia, the postulated, Mars-sized planetoid that smashed into the early Earth and launched a large chunk of it into orbit.

It might sound like a crazy idea, but there’s a decent amount of evidence for it.  There are still kinks to be worked out, like why the Moon’s oxygen isotopic ratios are almost identical to those of the Earth instead of a hodgepodge of ours and the impactor’s, but other similarities in composition actually bolster the hypothesis.  Then you’ve got all the lunar evidence of its impactful origin.  The crystal structure of many of the Moon’s minerals point to a molten beginning, which is hard to come by for a small body without the injection of large amounts of energy, e.g. being blasted off of somewhere else.  Zinc isotopes in particular seem to have been fractionated and volatilized, processes that don’t occur during run-of-the-mill geologic conditions.

And thank goodness it happened.  If the Earth had cooled without disturbance, most of the useful and precious (heavy) metals should have drifted down into the core.  The fact that we have significant amounts of iron, silver and gold so close to the surface is more evidence that something annihilated itself against Earth, leaving its core materials down below, allowing us to make things like cars, computer chips and keychains that make fart noises.  All of which would be useless if life hadn’t come together in the first place, which some think, amazingly, can also be attributed to the Moon.  Shorter, stronger tidal cycles 4 billion years ago may have provided the right changing environments to teach the first “protonucleic acids” how to replicate, leading to the formation of DNA and RNA, the building blocks of us all.

“I just wanted to say … thanks for being there, man.”  Image credit to

But the Moon didn’t stop exerting its beneficial influence there.  Once life got chugging along, the tides may have continued to force adaptations by hurling the fledgling organisms into unfamiliar territory.  Those strong early tides also squeezed and stretched the Earth itself, causing surface displacements up to a kilometer a day, kinetic energy that would slow the planet’s cooling and keep plate tectonics — and thus the carbon cycle — moving.  The Moon’s gravity also helped stabilize our axial tilt, which may have varied wildly without it.  An irregular wobble could have prevented the normal seasons we’re used to and hence made it difficult for complex organisms, that can’t adapt rapidly, to develop.


While it may not mystically control your personality, the Moon has gone a long way into making you who you are.  With all the mentions of it here, have you figured out why the tides were more frequent and stronger in the ancient past?  The Earth was rotating faster, only to be slowed gravitationally by that big hunk of cheese.  So you can also thank the Moon for a weekend that’s twice as long.  The tides were stronger because the Moon was actually closer to us back then.  Its orbit expands as time goes on.  We live at the exact right time for eclipses to occur!  Pretty darn awesome.

Much of the information here was taken from the very informative “How Earth and the Moon interact” from Astronomy Today.

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