What is the world's oldest slice of mantle, and how did it reach the surface?
Today, we'll meet the first tangible piece of the world below the crust, a world humans still have not visited. Along the way, we'll meet an old mineral friend from Season 1, a researcher named Friend, and learn how diamonds can be a geologist's best friend when looking for slices of the mantle.
Extra Credit: Clean your bathtub, or call an old friend.
