🧅 Earth's layers

Earth is built like layers of an onion, starting with a thin, rocky crust on the outside, the only layer humans have ever directly touched or drilled into. Underneath that sits the mantle, a much thicker layer of extremely hot, slowly flowing rock that makes up most of Earth's total volume. At the very centre sits the core, split into an outer layer of liquid metal and a solid inner ball, both incredibly hot despite being buried thousands of kilometres beneath your feet.

Earth's core stays hot for a couple of main reasons, leftover heat trapped since the planet first formed billions of years ago, and heat constantly being generated today by tiny amounts of naturally radioactive material breaking down deep inside. Rock is an extremely poor conductor of heat, meaning it traps warmth far better than it lets it escape, so all that heat has nowhere fast to go, even after billions of years. Scientists estimate the very centre of Earth is roughly as hot as the surface of the sun, an almost unbelievable temperature to imagine existing right under our feet.

Since the deepest hole ever drilled barely scratches Earth's thin outer crust, scientists mostly study the deeper layers by tracking how earthquake waves travel and bend as they pass through different materials underground. Waves speed up, slow down, or even bounce back entirely when they hit a boundary between layers, and scientists use those exact changes to map out what each layer is likely made of. Scientists also study meteorites, chunks of rock from space thought to be similar to Earth's deep layers, and volcanic rock that has occasionally carried up tiny samples from far below the surface.

Earth acts like a giant magnet, and that magnetic field is created deep inside by swirling, flowing liquid metal in the outer core, moving in a way that generates electric currents and, in turn, magnetism. This invisible field stretches far out into space, forming an enormous protective bubble that deflects most of the dangerous charged particles constantly streaming from the sun. Without that protection, those particles would strip away much of Earth's atmosphere over time, so the magnetic field plays a surprisingly important role in keeping the planet livable.