Finally, 3.7 billion years ago, we reach some of the strongest evidence for life on Earth yet. It takes a while to find, and it only looks like a few dark crystals, but it's better than anything else we've seen so far. Along the way, we'll meet three scientists who helped define the quest for Earth's oldest fossils, including one of my old bosses.

Extra Credit: Sharpen your pencils, spackle some cracks, or thank a mentor in your life.

This episode, we focus on just one special boulder from the Greenland tundra, a rock that might have Earth's oldest fossils. Over the past 10 years, scientists from around the world have used the latest technology to reveal this rock's secrets, including research published this year. What have they found?

Extra Credit: Make a time capsule or play a record.

Until now, all the clues for ancient life have been microscopic, beyond the realm of sight. Today, that begins to change. Ten years ago, a team of scientists showed the world a weird, lumpy rock that they claimed was the oldest microbial colony. Like a sci-fi movie, this specimen was found under melting ice in the high Arctic, unveiled from 3.7 billion years ago. But is it actually a fossil? Welcome to the debate that has defined my corner of geology.

Extra Credit: Check your house for hard water damage, or watch The Thing (1982).