Richard Dixon Oldham

Geologist and seismologist, the discoverer of the Earth's core, born in Dublin, Ireland. He studied at the Royal School of Mines, was a member of the Geological Survey of India (1878–1903), and became director of the Indian Museum in Calcutta (from 1903). His report on the Assam earthquake of June 1897 distinguished for the first time between primary and secondary seismic waves. In 1906 he established from seismographic records the existence of the Earth's core.

Richard Dixon Oldham (July 31, 1858 – July 15, 1936) was a British geologist who, in 1906, argued that the Earth must have a molten interior as S waves were not able to travel through liquids nor through the Earth's interior.