The simulations were a big undertaking, but the results are in: Without our moon, we would, indeed, suffer larger swings in Earth’s tilt. But here’s the good news: Even over the course of hundreds of millions of years, these swings are not fast and traumatic. Lissauer’s team reckons that the tilt of a moonless Earth would be stable enough, for long enough, to allow complex life to gain a claw-hold, or at least to adapt to new environmental circumstances when the poles moved.