For a long time, explorers thought the earth was flat. We know it's not, but why is it round? Roger Joyner from the Greensboro Science Center says it all has to deal with gravity. WFMY

GREENSBORO, NC -- The early explorers thought the earth was flat and you could sail right off the edge.

We know that is not true, but Phinally asks a great question, "Why is the planet round?"

In getting an answer to this question, we found the earth's circumference, right at the equator, is 24,901 miles. So, why is the earth round? Roger Joyner from the Greensboro Science Center explains.

"It all has to do with gravity. Everything has gravity. You have gravity, I have gravity. The earth has gravity."

Anything bigger than 600 miles across has enough gravity that it pulls itself together. Roger used play-doh to help illustrate the point. "If an object has enough gravity it would pull all towards the center. It all pulls towards the middle and eventually it will make that object, whatever it is, more or less round. Its big enough, it's gravity is strong enough to pull itself into this round shape."

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