A snowball Earth. Scientists believe this happened at least twice in Earth's history. But what caused these extreme ice ages? | The Brain Maze

Tunguska, 1908 — a cosmic explosion 5 miles above Earth. It never touched the ground… Yet it flattened 820 square miles of forest. The force? Equivalent to a 15 megaton hydrogen bomb — nearly as powerful as the largest the U.S. ever tested. And unlike a crater-causing impact (like Arizona’s Meteor Crater), this one vaporized midair—snowball vs. cast iron. This is what a space rock can do... without even landing. Still think we’re safe? | The Randall Carlson