The Earth and Moon: A Love Story

A non-scientist's take on what makes the Moon so great.

A long, long time ago (roughly 4.5 billion years ago, actually), in a galaxy not so far away (our Milky Way) the Earth was a boiling ocean of hot magma, spinning in space, minding its own business. Not long after that, (about 30 million years later, which, in the lifetime of the universe, isn't very long at all) a big bully of an asteroid about the size of Mars struck the magma-ocean Earth a glancing blow. This blow knocked the hot rock out of the proto-planet, broke the asteroid into pieces and also splashed a huge glob of the magma ocean out into space. Eventually, the two magma globs cooled to form the Earth and the Moon.

Or, maybe the boiling magma ocean began spinning too fast and eventually broke apart to form two separate celestial bodies: the Earth and the Moon.

Or perhaps, after the Earth was formed, she caught the eye of a large passing asteroid and pulled him onto the galactic dance floor. Why, hello there, Moon. I haven't seen you 'round these parts before. Care to dance?

Well, no matter how it happened, the end result is a love story for the ages.

If you are like most people I know, you would probably shrug if I asked if you looked at the Moon last night. This really is a shame; our Moon is not only beautiful, it's also our closest celestial neighbor. Beyond the obvious importance of our Sun, it's also pretty essential to the continued existence of life on this planet. Since the Moon affects liquid on the Earth, some scientists have postulated that as the Earth's magma ocean cooled into layers during the creation of the planet, the pull of the Moon's gravity may have triggered the formation of the Earth's separate plates and influenced the start of the tectonic cycle. I bet you know this already, but the Earth's ocean has regular tides because of the Moon, and because I know you also paid attention in science class in middle school, you know that water is essential to the existence of life on Earth (which is why we're all so curious whether there's any on Mars). The Moon effects not only the tides, but also the currents in the ocean, helping to maintain the oceans' temperature and moving nutrients around the globe. Beyond that though, the Moon also helps keep the Earth's rotation stable as we move around the Sun, giving us four distinct and lovely seasons.

But what would happen if the Moon were to inexplicably disappear?

With the exception of the Earth's continued rotation and the slight influence of the Sun's gravity on our oceans, the tides would slow dramatically; maybe even stop entirely! Despite the size of the Sun (and its larger gravitational pull compared to the Moon), its larger distance from the Earth means its effect on Earth's oceans is weaker than the Moon's. The tide itself is actually a bulge in the water as the gravity of the Moon pulls it. Inertia creates a matching bulge of water on the opposite side of the Earth, and because the Earth rotates the tides are cyclical. You know the tides help recirculate nutrients; they also help fish breed, stabilize the ocean temperature allowing life to thrive, and also maintain global temperatures. Without the tides actively swirling the water in the oceans, pollutants in the water would stay in place rather than dissipating naturally, the food supply in the ocean would diminish, and hot and cold pockets in the ocean would cause problems with the Earth's climate. This is bad, but it isn't even the worst possibility!

What could possibly be worse? Let me tell you!

A slight wobble is inherent in the Earth's rotation; her axis isn't perfectly upright, it's slightly tilted (between 22° and 24°, depending on a lot of math)! The Earth is pulled on by both the Sun and the Moon, and since our beautiful Moon helps stabilize Earth's axis, losing the Moon could possibly disrupt it! Without the balancing pull of the Moon, the axis could become unstable, causing the planet to wobble wildly. Since the seasons on Earth depend on the gradual change in angle and direction of the axis during orbit in relation to the Sun (this is called precession and obliquity, respectively), this wobble would be disastrous. The Earth would no longer have four distinct seasons, which could eventually lead to the death of life as we know it.

It all sounds so dire, right? Luckily, we do have that big, beautiful, smiling man in the Moon up there, and if it weren't for the creation (or seduction) of the Moon billions of years ago, there's a huge possibility that life on Earth would never have evolved. Without the Moon sticking around, our planet would slowly wither away. See what I mean about a love story? The Moon gives the Earth rotational stability, influenced the tectonic-cycle and the movement of the tides, the circulation of ocean nutrients and temperature regulation, and makes this beautiful blue marble we call Earth into a place that can sustain life. So, the next time you're out on a moonlit walk with your love, take a minute to admire the Moon.

Carynn Weber, Dynetics


7. and earth's orbit


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