Journey beneath Earth’s surface to examine the core, mantle, internal heat, pressure, and density. Evidence from seismic waves, experiments, and planetary physics reveals a deep structure that cannot be observed directly.
Some of Earth’s most persistent volcanic regions occur far from the boundaries between tectonic plates. Hawaii is the classic example: a chain of volcanoes crosses the middle of the Pacific Plate, with progressively older islands and seamounts extending away from the currently active end. One...
Far below Africa and the Pacific Ocean, the deepest mantle contains two structures so large that geophysicists often compare them with continents. They are called large low-shear-velocity provinces, or LLSVPs. Despite the nickname “blobs,” they are not hollow chambers, buried continents, or neatly...
The last few hundred kilometers of Earth’s rocky mantle bear an old, understated label: D-double-prime, usually written D″. The name suggests a tidy layer. Seismic evidence instead reveals a shifting mosaic of fast and slow material, abrupt boundaries, continent-scale structures, and thin patches in...
Snow may exist thousands of kilometers beneath Earth’s surface, but not as ice and not in any sense that could be watched directly. In one influential model, tiny iron-rich crystals form within a slurry at the base of the liquid outer core, settle under gravity, and accumulate on the inner core. The...
Every substantial earthquake sends energy through the planet along many routes. Seismometers at different distances record those arrivals, but some direct waves vanish across broad arcs of Earth’s surface. These gaps are seismic shadow zones. Far from being empty information, their positions expose...
At Earth’s center, temperatures are comparable to those at the visible surface of the Sun. Yet the innermost part of the planet is not a molten sphere. It is a solid body about 1,220 kilometers in radius, enclosed by a much larger layer of liquid metal. The contrast seems contradictory only if...