The beginning of Earth started out when Gaea "realized" she was lonely. Which was pretty much obvious, but not for long, in another strip, she get kids, really bad kids.
Storyboard Text
Yup, it's me. Gaea, mother Earth, or " Big Mama," I created the Earth, you know, the works.
It's hard work being the creator of Earth, I'm so lonely.
Hey, DON'T LAUGH. You'll get there one day, you little twerps.