How underground rocks make hydrogen gas for fuel

HostMost of us think of fuel as something we either have to make in a factory, like batteries, or something dirty we dig up, like oil or coal. But it turns out there might be a third way. There's a clean, powerful fuel that the earth seems to be making all on its own, deep in the ground, and we only just started looking for it. How's it even possible for plain old rocks to just breathe out hydrogen gas?

GuestIt's one of those things that was hiding in plain sight because we simply told ourselves it couldn't exist. For a long time, the rule in science was that hydrogen is too restless to stay under the ground. It's the lightest thing in the world, so we figured if any was down there, it would've leaked into space billions of years ago. But then, back in the eighties, a group of villagers in Mali were digging for water and hit a dry hole instead. A guy leaned over it with a lit cigarette, and the whole thing blew up in his face. It burned with a strange, clear blue flame for weeks.

HostThat sounds like a lucky break for the guy with the cigarette, but wait. If it was burning for weeks, that means it wasn't just a little pocket of gas that puffed out and went away.

GuestRight, that's the big shift in how we think about this. Usually, when we find gas or oil, it's like a tank that we slowly empty. But in that spot in Mali, they eventually hooked a small engine to the well and it has been making power for the village for years, and the pressure hasn't really dropped. It looks like the earth is actually making the stuff in real time. It's not a tank; it's more like a tap.

HostOkay, but how? Rocks aren't alive. They don't have energy to give away. What's actually happening down there to create a gas out of nothing?

GuestIt's mostly a simple trick of chemistry that happens when water meets a certain kind of rock. Deep down, there are these huge slabs of rock that are very rich in iron. When water seeps down and touches that iron, a reaction kicks off. The iron basically steals the oxygen right out of the water. It's a bit like a fast version of rusting. When the iron takes the oxygen, the hydrogen that was in the water is left all by itself. It turns into a gas and starts bubbling up through the cracks. There's another way it happens too, where tiny bits of natural radiation in the earth strike water and split it apart. But the rusting rock thing seems to be the main engine.

HostSo if this is happening everywhere there's iron and water, does that mean we're sitting on a gold mine? Why are we still building giant wind farms to make hydrogen when we could just poke a straw in the ground?

GuestWell, the catch is that we don't really know how much of it's actually trapped. Since hydrogen is so tiny and fast, it can slip through almost anything. To find a big pile of it, you need the right kind of rock making it, and then a very solid, thick layer of different rock on top to act like a lid. If there's no lid, the gas just drifts away into the air. We're finding these lids in places like France and the middle of the United States now, but we're still learning how to spot them from the surface.

HostI'm struggling with the idea that this is clean. We have spent years hearing that digging stuff out of the ground is what got us into this mess with the climate. Is this really any better than gas or oil?

GuestIt's much better in terms of carbon, because when you burn hydrogen, the only thing that comes out of the tailpipe or the chimney is water vapor. No smoke, no warming gases. But you're right to be cautious. Hydrogen itself isn't a greenhouse gas that traps heat directly, but if it leaks into the sky, it can mess with the way other gases break down. It kind of keeps the bad stuff like methane around longer. So, we have to be incredibly careful not to let it leak while we're pulling it up.

HostBut is it actually a big enough deal to replace what we use now? It feels like we're talking about a few lucky wells here and there, not a global solution.

GuestThat's what the big science groups are trying to figure out right now. Some early guesses from the government say there could be trillions of tons of this stuff down there. Even if we can only get to a small part of that, it would cover our energy needs for hundreds of years. And remember, because the rocks keep rusting as long as there's water, some of these spots might actually refill themselves. It's not like a coal mine where once it's gone, it's gone. It's a living system.

HostSo we might be looking at a world where we don't have to choose between keeping the lights on and keeping the planet cool.

GuestThe real test is going to be the cost, because if it costs more to drill for this than it does to just make it with solar power, it stays a dream, but for now, the chase is on to find where the earth is hiding its best fuel.

HostIt's wild to think that while we were looking up at the sun for clean energy, the rocks under our feet were busy making it the whole time.

GuestThose iron rocks in the deep dark are still down there turning water into power, just waiting for us to find the lid.

HostThe next time I see a rusty old pipe or a red rock, I'll be thinking about that blue flame burning in the middle of a desert.