How to discover a region of the Earth that no one can reach? Danish seismologist Inge Lehmann works with surface-recorded traces. Earthquakes produce waves whose path and arrival depend on the materials passed through. These distant movements become a way of questioning the interior of the planet.
By examining the records, Lehmann defended in 1936 the existence of an inner core within the Earth's core. This structure allows to explain the behaviour of waves that the previous model did not adequately describe. The discovery is based on a demanding reading of the signals and their physical interpretation, not on a sample raised from the center.
The GEUS, geological service of Denmark and Greenland, recalls the role of its instruments and calculations. One of his old seismographs was installed in a fortified structure near Copenhagen. This modest place was part of a huge investigation: to understand the deep architecture of the Earth by observing how it trembles.
What we know
A deduction from seismic waves, not a visual observation of the nucleus.
To go to the source
References consulted on September 21, 2026. Linked pages may be in another language.
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