Inge Lehmann discovered Earth’s solid inner core by analyzing seismic waves in 1936.
Lehmann was a Danish seismologist who studied how earthquake waves travel through Earth. In 1936, she published evidence that the planet’s central region was not a single liquid mass. Instead, she proposed a solid inner core surrounded by a liquid outer core. Her conclusion came from unusual seismic waves detected after distant earthquakes.
The inner core is difficult to observe directly because it lies roughly 5,000 kilometers beneath the surface. Seismic waves provide an indirect method: their speeds and paths change when they encounter materials with different physical states. Later measurements confirmed Lehmann’s interpretation and refined estimates of the inner core’s size and composition. The inner core is mostly iron and nickel, while the liquid outer core helps generate Earth’s magnetic field. Lehmann continued working in seismology for decades and lived to be 104.