Abiotic hydrocarbons via hydromagnesite–FeO redox reactions

• A new abiotic pathway for hydrocarbon formation from carbonate–FeO redox reaction is proposed. • Ethanol and acetaldehyde are detected under mantle P–T conditions, revealing O-bearing intermediates. • Abiotic hydrocarbons form via stepwise deoxygenation and reduction of carbonates. Abiotic formation of hydrocarbons within the Earth’s deep interior represents a crucial aspect of the global carbon cycle. Understanding the process from carbonates (oxidized state) and hydrocarbons (reduced state), and the compositional distribution of hydrocarbons at various deep-earth pressure–temperature conditions are essential for improving carbon cycling models. Here we studied the chemical reactions among hydromagnesite, H 2 O, and FeO under the deep Earth conditions (10–20 GPa, 900–2100 K), employing diamond anvil cell coupled with laser/resistive heating techniques as well as large volume press. The experimental results reveal a progression from saturated to unsaturated hydrocarbons with increasing P-T conditions. More importantly, we identified ethanol and acetaldehyde in the recovered product. This indicates that the reduction process of carbonates involves multiple intermediate processes, and complex organic compounds can be stabilized at suitable conditions. Our study provides new insights into the mechanisms of hydrocarbon formation in the deep Earth.