Reference

The evidence supporting the abiogenic formation of alkanes in Earth's crust includes:

1. Unusual patterns of carbon isotope ratios (δ13C values) among C1-C4 alkanes, which suggest an abiogenic formation mechanism.
2. Progressive isotopic trends for the series of C1-C4 alkanes, indicating hydrocarbon formation through the polymerization of methane precursors.
3. The presence of abiogenic alkanes in various locations worldwide and on other celestial bodies, which implies a non-biological origin.
4. The chemical composition of abiogenic alkane gases, which often has a low methane content and lacks C2+ hydrocarbons.

For more detailed information, refer to the research article titled "Abiogenic formation of alkanes in the Earth's crust as a minor source for global hydrocarbon reservoirs" published in Nature. Source