Methane could be forming in Earth’s mantle, US scientists have shown. The result suggests that untapped and unexpected reserves of natural gas and oil may exist deep beneath the planet’s surface. Fossil fuels such as oil and natural gas are organic materials made up of carbon and hydrogen. The consensus view is that all commercially viable petroleum and natural gas is made by biological processes – although methane can also be made in small amounts within volcanoes. In fact, the recent detection of methane in Mars’s atmosphere has been interpreted as evidence either of ongoing volcanic activity or of life.