Form 8655 Magnetic 2024

How does the earth generate its magnetic field? Okay, so the earth self-generates a planetary-scale magnetic field in its core. Let me first mention that here's earth, where we live. Right there, that's us (not to scale). Right now, our head is far out in space. We would quickly perish. But here's our planet, and if you cut a cross-section through it, the inner half is predominantly liquid metal. However, the pressure gets so high in the middle that the innermost third has actually solidified. So, this part is solid and this part is liquid. It's all predominantly iron, with some nickel and some other stuff. Let's say it's mainly iron, nickel, and other stuff. For today, let's just say sulfur. It could be a couple of things, but we'll choose sulfur. Okay, so here's our planet. We've got, for the most part, solid silicate in what's called the mantle. And this core, about the size of Mars, is predominantly liquid. It's big, the size of other planets. This planet, our planet, all planets, are radiating heat out to space. And that causes the mantle to actually be overturning. But if it's solid, how is it overturning? It's overturning on about a 500 million year timescale. It's solid-state convection. This is the beauty of plate tectonics. That's a whole other story. But the mantle is overturning roughly every 500 million years, really slow. And yet, we can map it all out. It makes a lot of sense. Okay, so very slow overturn of the mantle, that though it's allowing heat also to escape from the core. So the core is cooling down, as well as the mantle. And as the core cools down, one of the most interesting things is that as the temperature decreases, the inner core grows outward...