Many folks have claimed to find Earth's oldest fossils in the Greenland rocks, 3.7 billion years old. Before we meet and judge these contenders, we need to learn what counts as a fossil. This early in Earth history, nothing has any bones or teeth or shells, so researchers need to search for other clues. Today, I'll show you four ways to look for fossils in Earth's oldest rocks, including my personal field of study: fossilized bacteria.

Extra Credit: Find different types of organic carbon in your day, or eat a burger.

What is the hardest rock to make?

Today's rock is very common in Earth's ancient past, and it should be everywhere today. However, it's nearly impossible to form in nature or the laboratory. Some experiments have tried for 32 years with no success! This rock is dolomite. Today, we address The Dolomite Problem, one of geology's longest-running mysteries. Along the way, we'll meet some smelly but helpful bacteria, sort a fruit stand, and learn about the cutting edge of geology research.

Extra Credit: Eat some citrus, and check your home for natural gas leaks.

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Today is a tale of two sisters: limestone and dolomite. Limestone is far more popular and well-behaved, one of the most common stones in nature and in architecture. Dolomite, though similar in many ways, is one of the most difficult rocks to make on Earth. Even dolomite’s name is a bone of contention. Today, we introduce both siblings to the show as we move forward in time, 3.75 billion years ago. Along the way, I’ll give you a real experiment to try in the kitchen and we’ll smash some stones together.

Extra Credit: Try today’s kitchen experiment, find some limestone around you, or get some calcium in your diet (dairy, leafy greens, or tofu).

What types of volcanoes were erupting 3.8 billion years ago?

Today, we meet a new type of rock and a new type of volcano, far more powerful and dangerous than those we've met so far. The old volcano is long dead, but the scars it left behind can still be seen across the Greenland landscape. Along the way, we'll learn how different types of lavas are made, why a few rocks can float in water, and learn about a field trip Dylan took to Iceland in 2010.

Extra Credit: Eat a grilled cheese sandwich, blow a bubble in gum, or make campfire.

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.

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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.

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In 1971, two geologists traveled to the edge of Greenland's ice sheet. What they found were the oldest rocks known at the time, 3.8-3.7 billion years old.

Shockingly, they were in decent condition, sparking a half-century of geology stories. Today we'll begin our tour of Isua, the final destination of Season 2. Along the way, we'll meet a Holocaust survivor who landed on top of the world, visit an iron mine surrounded by glaciers, and start to meet the highest-quality rocks of this season.

Extra Credit: Eat some candy, some shrimp, or some Indian food.

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Two months ago, I made an audience survey focusing on one topic: how would you like to support the show?

Many folks answered, and here's what you said about donations, Patreon, ads, and merch.

If you want to give your own opinion, take the survey here, put a comment below, or send a message to [email protected].

If you'd like to give a donation, you can click here- any amount is appreciated!

Nearly 30 years ago, one paper claimed to find the oldest evidence for life on Earth. How does that evidence hold up in 2025? Are these fossils or duds? Don’t panic, we’ll answer these questions to life, the universe, and everything in due time. Along the way, we’ll meet the most abundant mineral in the human body, an important fertilizer, and finish a trilogy of intense debates over a small Greenland isle.

Extra Credit: Read The Hitchhiker’s Guide to the Galaxy, eat cake with sprinkles, and make sure to floss afterwards.

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Click here for the audience survey!

Click here to read Dylan's Nature paper!

In 1991, a mysterious, striped red and gray rock was discovered on a cold Greenland isle. Years later, this rock would rock the scientific world with multiple debates about the early oceans and life. What exactly is this rock, and why do we care? Stay tuned, and on the way, we’ll learn how scientists can officially argue with each other.

Extra Credit: Eat something with peanut butter and chocolate, pet a large and a small dog, or make sure your vaccines are up to date!

Donate to support the show- anything is appreciated!

Click here for the audience survey!

Click here to read Dylan's Nature paper!