There's a long-held belief that life as we know it on Earth wouldn't exist without the moon.
However, new evidence suggests that this is wrong and that we really never needed the moon at all.
After running computer simulations about Earth's habitability without a moon, a team of scientists - Jack Lissauer of NASA Ames Research Center, Jason Barnes of the University of Idaho and John Chambers of the Carnegie Institution for Science - now believe that the moon doesn't affect life on Earth as much as we originally thought.
In the 1990s, a French astronomer named Jacques Laskar ran his own simulations and determined that the moon played an important role in keeping our planet tilted at the same angle. This tilt, called obliquity, is important because if it isn't stable, it creates chaos on the surface of the planet, as well as crazy weather, both of which are not conducive for supporting life.
However, Laskar worked with computers of the 1990s, which, as we know, weren't as fast and couldn't handle as much data as today's modern computers. So it's not much of a surprise that when running similar, but more, data through a computer in the 2000s, we see different results.
After Lissauer, Barnes and Chambers ran their simulations through a modern-day computer of the Earth without the moon, they discovered that Earth's tilt would only wobble about 10 more degrees, which is relatively minor.
"To test our code we began with integrations following the obliquity of Mars and found similar results to other people," says Lissauer. "But when we did the obliquity of Earth we found the variations were much smaller than expected - nowhere near as extreme as previous calculations suggested they would be."
The team also discovered that if Earth spun faster, with a day being 10 hours rather than 12, then it still remained relatively stable, thanks to the gravity of other planets in the solar system, such as Jupiter.
In other words, we don't really need the moon. And neither do other potentially habitable planets. This study shows that planets capable of sustaining life don't necessarily need the influence of a moon.
Other researchers point out that a large moon can actually make a planet that would otherwise be habitable incapable of sustaining life because of how a moon affects a planet's tilt. Planets that sit on the edge of their habitable zones, or that spot that's neither too close or too far from its star, are particularly affected by having a moon. Without a moon, their tilt is greater, meaning that they get more heat from the sun, creating water on their surfaces. However, with a moon, there is less tilt, meaning those planets get less heat and are more likely to have frozen environments, similar to Mars.
The moon possibly played a minor part in Earth's history, though, at least when it comes to life. Scientists believe that the moon helped create tidal pools on Earth, where life probably originated on the planet. However, the sun also affects tides, so it's possible, the moon's part in making Earth so life-friendly wasn't that important.
