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.

What was Earth's mantle like 3.8 billion years ago, and how do we know?

The mantle is a realm that humans have never visited, and examining it is only harder in the ancient past. Fortunately, the mantle sometimes gifts us with beautiful green rocks from the deep, souvenirs of an unknown underworld. Today, we learn how the mantle has changed over time, and its surprising connections to outer space. On the way, we'll meet the father of geochemistry, revisit old asteroid friends, and learn why you should always flour your berries before making a cake.

Extra Credit: Bake some blueberry muffins.