What is the oldest thing on our planet? How old is it, and where was it found?

Today, we tell the story of a worldwide, decades-long hunt for a single grain of sand. We'll journey to underground magma chambers, the sun-baked Australian Outback, and the lair of a giant shrimp.

Extra credit: Let a handful of sand run through your fingers, or go pressure-wash something.

The idea of plate tectonics is the cornerstone of modern geology.

But it wasn't always that way, and it wasn't an easy idea to sell. Today, we'll meet two scientists who faced ridicule for proposing continental drift: a German climatologist and an American cartographer, the greatest of her generation. We'll also meet a lost expedition to Greenland, the Mid-Atlantic Ridge, and Jacques Cousteau.

Extra credit: Look at maps of the ocean floor, or try to align the continents in various patterns on a map.

How is new crust made, and why isn't the Earth constantly expanding like a party balloon? To answer these questions, we'll track the life, death, and rebirth of Earth's surface. Stops along the way include the Mid-Atlantic Ridge, a prize-fight between tectonic plates beneath New Zealand, and a stop for dessert on the Italian island of Vulcano.

Extra credit: Experiment with your carpets at home, pushing them together and testing which one sinks beneath the other.

When did Earth's crust form?

It's easy to take the ground beneath our feet for granted, but the story of our crust's origins is one of the most hotly debated topics in Earth history. Today, we'll learn about how elements inside zircon crystals can help solve this mystery. In fact, the element hafnium was discovered inside a zircon by two researchers who also helped keep gold and scientists out of German hands in World War II.

Extra credit: Look at table salt under a microscope, or find different colors of quartz in your local mineral collections.

How did water arrive on planet Earth?

Today, we learn just how much water Earth has (spoiler: probably not as much as you'd think), and where it came from in the first place. We'll take a joyride around the early solar system, learn how our stellar neighborhood is like a snow-capped mountain, and discover how the planet Jupiter might have played a crucial role in creating the oceans of Earth.

Extra credit: Drink some water, make a snowball, or watch the Kevin Costner classic Waterworld.

How do we know when the first oceans existed?

Water leaves its' fingerprints over every surface of Earth, even in the oldest, toughest crystals. Today, we'll take an imaginary ride through the earliest oceans, examine how water slowly transforms everything it touches, and how these changes are recorded in the Jack Hills zircons, 4.4 billion years ago.

Extra Credit: Make an underwater rock garden, walk into a muddy beach, or visit a dog park.

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