Dear Penny,

Blue oceans, green forests, a cozy blanket of oxygen. Our planet is a super comfy home. It’s hard to imagine there was ever a time it didn’t exist.

I asked my friend Julie Ménard how Earth formed. She’s a planetary scientist at Washington State University.

She told me it started with the Big Bang. That was nearly 14 billion years ago.

“The Big Bang is not an explosion,” Ménard said. “It’s an expansion. Everything in our universe today was in a tiny spot—smaller than the eye can see. Eventually, the pressure and density got so high that it started to expand.”

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