Part of the show Peruvian Mummies, Ancient Environments and the Sahara
John in Colchester asked:
Did oil or natural petroleum deposits really come from primordial forests? With the thousands of barrels of oil taken out every day, there must have been an awful lot of trees.
Oil is the rotten remains of trees and other vegetation. If you go back to the time of the oil and certainly the coal-bearing strata we have in the British Isles, the British Isles wouldn't have looked like it did today. It was significantly further south towards the equator and therefore had a much more tropical climate. The nature of the vegetation would have been similar but not identical to perhaps modern tropical rainforests. As they died and fell down, they were buried over long periods of time, compressed and ultimately that forms oil. Quite a lot of oil is made from algae in the sea. Algae gets cooked when it's buried deeply. That gives off oil which floats up nearer to the surface.