Why Does The Earth Have Levels?

...or why do we live on an onion made of magma? Viewers like you help make PBS (Thank you 😃) . Support your local PBS Member Station here: https://to.pbs.org/PBSDSDonate Subscribe to It's Okay To Be Smart: http://bit.ly/iotbs_sub Thanks to Miles Traer and Mike Osborne for geophysics help on this one! Why does Earth have a liquid core, and how do we know? http://scienceblogs.com/startswithabang/2011/09/28/why-does-the-earth-have-a-liqu/ How many pennies would you have to stack to melt the one on the bottom? http://www.reddit.com/r/askscience/comments/2g8jj9/how_many_pennies_need_to_be_stacked_before_the/ Why are the inner planets rocky and the outer ones are gas giants? http://www.quora.com/Why-are-the-inner-planets-rocky-and-the-middle-planets-large-gas-giants Produced for PBS Digital Studios Joe Hanson - Host and writer Joe Nicolosi - Director Amanda Fox - Producer, Spotzen IncKate Eads - Associate Producer Katie Graham - Director of Photography Andrew Matthews - Editing/Motion Graphics John Knudsen - Gaffer Dalton Allen - Post-production Intern Theme music: "Ouroboros" by Kevin MacLeod Stock images via Shutterstock ----------- Join us on Patreon! https://patreon.com/itsokaytobesmart Twitter http://www.twitter.com/DrJoeHanson http://www.twitter.com/okaytobesmart Instagram http://www.instagram.com/DrJoeHanson http://www.instagram.com/okaytobesmart Merch https://store.dftba.com/collections/its-okay-to-be-smart Facebook https://www.facebook.com/itsokaytobesmartpbs/​ Learn more about your ad choices. Visit megaphone.fm/adchoices