There were also some dusty remains of an old star that had exploded long ago. The gas and dust were floating, swirling and spinning past each other - but they were all quite far apart. But then… a nearby star exploded, in what we call a supernova.

This supernova sent a shockwave of light and energy rippling across space, pushing some of the gas and dust towards each other. This gas and dust soon became a ball, which started to get bigger and bigger because of gravity.

Gravity makes everything in the universe move towards everything else - and when things get really big (like, planet-size big), they start to pull all nearby things towards it.

Then, a huge rock smashed into Earth and made it even bigger. And a little bit of rock flew off and floated into space to make the Moon.

So the Earth was just out there floating in space, near the Sun. But it looked totally different to the Earth we live on today.  There were volcanoes all over the place, with hot lava and gas everywhere.