Overview
Billions of years ago, Mars may have looked less like the barren red desert we know today and more like Earth—with a blue sky, flowing rivers, and even seas. What happened to turn a once-habitable world into the frozen, lifeless planet we see now?

On this episode of Big Brains, University of Chicago geophysical scientist Edwin Kite takes us on a journey through Mars’ hidden past. From evidence of a lost carbon cycle to theories about ancient climate swings, Kite’s research is rewriting the story of the Red Planet. But it’s not just about the past—his work is also at the forefront of a provocative question, especially in light of recent news of NASA's discovery of potential evidence of ancient life on Mars: Could humanity one day terraform Mars so it could support human life?

Related
Was Mars doomed to be a desert? Study proposes new explanation—UChicago News
Carbonate formation and fluctuating habitability on Mars—Nature
How did wet and warm Mars become a cold, barren desert?—Cosmos
Transcript
Paul Rand: Hello everyone. Before we get into today’s episode, we need to pause for some breaking news. Since recording this conversation, NASA has announced one of the most tantalizing discoveries yet in the search for life on Mars: evidence in a rock formation that could point to ancient microbial activity.

The Perseverance rover showed unusual mineral structures—things like “leopard-spot” patterns and signs of carbon-rich compounds. On Earth, these kinds of features are often linked to microbial processes. While NASA is careful to stress this isn’t definitive proof of life, it represents the clearest potential biosignature we’ve seen so far from Mars.

As you’ll hear in this episode, Kite's work on Mars’ climate history, water systems, and the conditions for habitability makes today’s discussion feel even more urgent—and eerily prescient—in light of this new research.

Paul Rand: Imagine that you stepped out of a time machine on the surface of Mars a billion years ago. What do you see? You might imagine you’d see a reddish sky, rocks in all directions, and deserts and dunes on the horizon.

Edwin Kite: Well, I think a big change is that you would probably see a blue sky.

Paul Rand: Wait, what?

Edwin Kite: The ground would probably be sludgy or muddy because there was snow melt or rain back then, and there would be streams and lakes over the surface.

Paul Rand: That’s Edwin Kite.