1. Presence of hydrocarbons in locations in Earth's crust w…

1. Presence of hydrocarbons in locations in Earth's crust where no life has ever existed, for example in the deep Earth's mantle rocks.
2. The discovery of methane on other planets where life is not thought to exist, such as Saturn's moon Titan.
3. The relative abundance of 'helium-3' in oil wells, which indicates a connection between oil and deep Earth processes.