Reference

The abiogenic origin of hydrocarbons in the Earth's mantle is supported by several lines of evidence:

1. Laboratory experiments have shown that hydrocarbons can be synthesized from inorganic precursors under high pressure and temperature conditions similar to those found in the Earth's mantle.
2. Hydrocarbons have been detected in meteorites and the upper mantle, suggesting an extraterrestrial source.
3. The isotopic composition of some natural gas deposits is distinct from that of biologically derived hydrocarbons.
4. The presence of hydrocarbons in geological formations that predate life on Earth.
5. The vast quantities of hydrocarbons found in the Earth's mantle, which exceed what could be explained by biological processes alone.

However, the abiogenic theory remains controversial, and the majority of the scientific community supports a biogenic origin for most hydrocarbons. For more detailed information, refer to the following sources:

• In-situ abiogenic methane synthesis from diamond and graphite under upper mantle conditions
• Abiogenic petroleum origin - Wikipedia
• Abiogenic Origin of Hydrocarbons: An Historical Overview