Complex sentence: The geothermal potential of the UK was investigated by a program funded by the UK government and the European Commission that ran from 1977 until 1994, and saw a Hot Dry Rock experiment drilled in Carnmenellis granite of Cornwall.
Split into simpler sentences: The geothermal potential of the UK was investigated by a program funded by the UK government and the European Commission that ran from 1977-1994. Which saw a Hot Dry Rock experiment drilled in Carnmenellis granite of Cornwall.