When did life arise on planet Earth?

Today, we look at the search for biological remains in the oldest minerals on Earth, the Jack Hills zircons of Western Australia, 4.4-4.0 billion years ago. We learn why carbon is an excellent building block for life, how to turn that carbon into diamonds and graphite, and why it's very hard to find conclusive fossils in very old rocks.

Extra credit: Try to find all the things in your house that have carbon in them. Bonus points if you can find graphite or diamonds.

My guest today is Dr. Joti Rouillard, a research fellow at the University of Science and Technology in Hefei, China. Dr. Rouillard talks about his research on the earliest fossils on Earth, microscopic bacteria 3.5 billion years old. It turns out, identifying a fossil bacteria is extremely difficult since they resemble other tiny non-living objects. We also talk about working in the Australian Outback, kangaroo encounters, and what happens when you mix alcohol and rocks.

Dr. Rouillard's email: joti.rouillard@gmail.com

What are the oldest disputed fossils on Earth? Why are they disputed?

Today, we wrap up our tour of Nuvvuagittuq in northern Quebec, 3.8 billion years old, March 3rd on the Earth Calendar. In 2017, microscopic rusty threads were discovered inside these rocks, thinner than a human hair. Were they bacteria, or something else entirely? Stay tuned to find out!

Extra Credit: Learn how to make a chemical garden, or find a piece of chert, flint, jasper, agate, or onyx.

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.

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.