Inge Lehmann

Born in Copenhagen on 13 May 1888, Lehmann trained as a mathematician before turning to seismology, spending years analyzing seismic waves that rippled through the Earth after quakes. In 1936 she noticed an anomaly: certain waves were arriving where theory said they shouldn't, bent by something deep and dense. Her explanation - a solid inner core within the molten outer one - held. She later identified another boundary, a shift in wave speed between 190 and 250 km down, now called the Lehmann discontinuity. She worked into her nineties and died on 21 February 1993, having cracked open the structure of the planet with a seismograph and a sharp pencil.