If Earth Had No Moon

What if Earth didn’t have a moon? Well, nearly everything about our home planet would be different—so much, we’d hardly recognize it. Our Moon is a quarter the size of Earth, far bigger than most planets’ moons. Scientists think it formed when a smaller planet crashed into Earth 4 billion years ago, knocking off a chunk that eventually became our Moon. Its large size is key to its dramatic effects on Earth. The gravity of the Moon pulls on the oceans to produce tides. Tidal range would be only a third its size otherwise. Tides define coastal ecosystems and influence what kind of life can live there. Tides also shape ocean currents—like the ocean conveyor we discussed on another EarthDate. Currents moderate global weather and temperature, helping create the stable climate that has allowed human civilization to thrive. Tidal friction has also slowed Earth’s rotation. Billions of years ago, a day on Earth lasted just 10 hours. Without the Moon, it would be even shorter than that! The Moon also stabilizes the tilt of Earth on its axis, which stabilizes our seasons. Planets without moons have much more dramatic seasonal variations. Adapting to erratic seasons and temperatures, and days as short as 6 hours—the plants and animals that could live on Earth would likely be very different. Without the Moon, humans might not be here at all!