Is this what people mean when they say “Many moons ago . . ?”
This is a really interesting thought experiment. And like most interesting thoughtsperiments (a word I just invented), we have to make a whole mess of rules right off the bat.
- We’re going to limit ourselves to one new moon, for a grand total of two, count ‘em, two moons.
- Did the new moon show up recently? Or was it there before life formed? We’ll look at both scenarios.
- We’ll assume that the new moon is about the size of our current moon.
One thing to remember about our current moon is that it’s pretty big. Sure, not as big as Jupiter’s moons, but relative to Earth? Huge. It’s 1/81th of the Earth’s mass, which is a big ratio for a moon. This means that our moon exerts a ton of gravitational force on Earth, and vice versa.
If we had a second moon show up, things would change in a hurry. Our tides would go haywire and cause massive storms, volcanoes and earthquakes to pop up from the added forces put on the Earth’s crust . Unfortunately for most things alive on Earth at the time, this would mean chaos, death and possible extinction. That includes us, but maybe not the bacteria or cockroaches. The second moon would also cause chaos on our first moon, causing similar geologic changes, although not as severe since Moon #1 is a lot more dormant on the inside.
If the second moon happened to show up before life on Earth began, then it would be a different story. We’re nearly 100% certain that life as we know it started as pretty basic single-celled organisms. And since they, and all life, would have evolved on an Earth with two moons, everything would adapt to that environment instead of the Earth we know today. That means that fish would respond to different tides, if they became fish at all, nocturnal animals would have more moonlight to hunt by, and almost nothing could live within a few hundred feet of shore … unless they liked to swim in tides hundreds of feet high!!
I honestly can’t find it in my pea-brain to decipher if the time to orbit the Sun would be different (anyone know the answer?), but our days and months would change. Eventually, after thousands of millions of years, the pull of two moons would force the Earth to stop rotating due to the friction of gravity on the tides. Of course, this will happen with one moon, too. We just have to wait longer.
So if life on Earth evolved to survive with two moons, we’d do what we do in the two-moon world we were doing it in. If it showed up tomorrow? Well, nice to know ya.
By the way, there’s a whole book about this. You know, if you need more :)
EDIT: Check out Jim Brown’s additional tidbits in the comment section below this post. Thanks for the extra info!