So, today I’m celebrating the Moon. The ancient mythology and modern physics of its stabilizing influence.

Both the Moon’s natural prominence in the earthly sky and its regular cycle of phases as seen from Earth have provided cultural references and influences for human societies and cultures since time immemorial.

After enjoying the full moon for July 4th, today this phys.org article reminded me about the role our Moon has played in Earth’s evolution, perhaps even critical to life as we know it.

Phys.org > “Higher concentration of metal in Moon’s craters provides new insights to its origin” by USC (July 1, 2020).

Life on Earth would not be possible without the Moon; it keeps our planet’s axis of rotation stable, which controls seasons and regulates our climate. However, there has been considerable debate over how the Moon was formed.

So, I searched for additional articles (below) on the claim that life on Earth would not be possible without the Moon. My impression is that life probably would have evolved, but not necessarily as we know it or in the same timeframe.

• Scientific American > “Without the Moon, Would There Be Life on Earth?” by Bruce Dorminey (April 21, 2009).

… four billion years ago a cooling Earth already had an ocean, but remained barren. The moon was perhaps half as distant as it is now, and as a result, the ocean tides were much more extreme.

… the moon is currently receding from Earth at a rate of 1.5 inches (3.8 centimeters) per year. As it does, Earth’s own spin rate is slowing. And, in the process, roughly 1020 joules of gravitational energy is shed into the oceans annually.

Molecular biologist Richard Lathe of Pieta Research, a biotech consultancy in Edinburgh, Scotland, contends that some 3.9 billion years ago, fast tidal cycling caused by the influence of our moon enabled the formation of precursor nucleic acids.

• Phys.org > “Did we need the moon for life?” by Fraser Cain (Nov 23, 2015).

When the moon was closer, the power of its gravity to pull the Earth’s water around was more ferocious. But what impact has this gravity had on our world and its life? Do we need the moon to make the magic happen?

Turns out, we might owe our very existence to it because its pull of gravity might have set our plate tectonics in motion. Without plate tectonics, our planet might be more like Venus, toasty and dead.

It raises the level of the world’s oceans towards the equator. Without this gravity, the oceans would redistribute, raising levels at the poles. It has also slowed Earth’s rotation on its axis. Shortly after its formation, the Earth turned once every 6 hours. Without that moon to slow us down, we’d have much more severe weather.

It stabilizes the Earth’s rotation on its axis. It’s possible that the Earth might have rolled over on its axis on a regular basis, causing a complete redistribution of the Earth’s water. Astronomers think this happened on Mars, because it never had a large moon to stabilize it.

But the biggest impact that the moon has on life is through tides. That regular movement of water that exposes the land at the edge of the ocean, and then covers it again just a few hours later. This could have encouraged life to adapt and move from the oceans to land.

• Space.com > “Moonless Earth Could Potentially Still Support Life, Study Finds” by Nola Taylor Redd (August 9, 2011).

… new simulations show that, even without a moon, the tilt of Earth’s axis — known as its obliquity — would vary only about 10 degrees. The influence of other planets in the solar system could have kept a moonless Earth stable.

The stabilizing effect that our large moon has on Earth’s rotation therefore may not be as crucial for life as previously believed, according to a paper by Jason Barnes of the University of Idaho and colleagues which was presented at a recent meeting of the American Astronomical Society.

The new research also suggests that moons are not needed for other planets in the universe to be potentially habitable.

• NASA > Facts About The Moon.

The Moon’s presence helps stabilize our planet’s wobble, which helps stabilize our climate.

• Inside Science > “What Would Happen If There Were No Moon?” by Marsha Lewis, Contributing Producer (Dec 2, 2015).

Nights would be much, much darker. The next brightest object in the night sky is Venus. But it still wouldn’t be enough to light up the sky. A full moon is nearly two thousand times brighter than Venus is at its brightest.

Without the moon, a day on earth would only last six to twelve hours. There could be more than a thousand days in one year! That’s because the Earth’s rotation slows down over time thanks to the gravitational force — or pull of the moon — and without it, days would go by in a blink.

A moonless earth would also change the size of ocean tides — making them about one-third as high as they are now.

Without a moon the tilt of our earth’s axis would vary over time. This could create some very wild weather. Right now, thanks to our moon, our axis stays tilted at twenty-three point five degrees. But without the moon the earth might tilt too far over or hardly tilt at all leading to no seasons or even extreme seasons.

Without the moon helping to keep the earth on a steady tilt, scientists have even imagined that life on earth may not have evolved the way we know it.