15: Sea Change

How do we know when the first oceans existed?

Water leaves its' fingerprints over every surface of Earth, even in the oldest, toughest crystals. Today, we'll take an imaginary ride through the earliest oceans, examine how water slowly transforms everything it touches, and how these changes are recorded in the Jack Hills zircons, 4.4 billion years ago.

Extra Credit: Make an underwater rock garden, walk into a muddy beach, or visit a dog park.