Geothermal

The story of the word

The word came out of nineteenth-century mine surveys, when engineers found that temperature climbs steadily with depth and started calling that rise the geothermal gradient. In ordinary crust it runs around 25 to 30 degrees per kilometre. Iceland, sitting on a spreading ridge, heats roughly nine in ten of its homes from the same source, and the Romans were already piping hot spring water into baths without a name for the physics.

How it travelled

Ancient Greek → scientific coinage → English

First recorded

19th century