Are there pockets of hydrocarbons, deep beneath the earth, waiting for exploitation by humanity? That was the question asked by Austrian-born astrophysicist Thomas Gold many decades ago, and the question of whether commercially significant natural gas can originate from inorganic chemical processes deep within the Earth’s lithosphere and upper mantle may, in light of recent studies, return to our geochemical discourse after all. While conventional petroleum geology maintains that virtually all extractable hydrocarbon accumulations derive from the thermal alteration of buried sedimentary kerogen, research published and field data gathered from late last year onwards appear to be challenging the paradigm.

Recent investigations spanning ab initio molecular dynamics simulations, oceanic core complex field sampling, thermodynamic reversibility models, and hydrothermal isotope fractionation experiments have introduced new empirical experimentation, among much else, into the ongoing debate over the volumetric significance of abiotic methanogenesis.

A central theoretical barrier to mantle-derived hydrocarbon models has been the assumption that carbon residing at upper-mantle conditions persists almost exclusively in oxidized states, primarily as carbon dioxide or carbonate ions. Six months ago, Stolte, Li, and Pan (JACS Au, 2026) published findings from ab initio molecular dynamics simulations evaluating the behavior of carbon-bearing supercritical fluids under pressure-temperature regimes representative of subduction zones and the upper mantle. Their calculations modeled aqueous fluids containing dissolved carbon monoxide and carbonate species at pressures ranging from 3.0 to 6.0 GPa and temperatures between 700°C and 1,100°C. The results demonstrated that water-rich supercritical fluids under these specific boundary conditions catalyze the spontaneous reduction and carbon-carbon coupling of inorganic carbon.

It yields low-molecular-weight alkane homologues: methane, ethane, and propane. The authors did note that rather than maintaining a strict oxidation state, dissolved carbon in dense aqueous environments undergoes polymerization via transient radical intermediates stabilized by the dielectric properties of supercritical water. While the study confirmed the feasibility of continuous abiotic synthesis along subducting slab interfaces, it left the question of upward migrations through the continental crust unaddressed.

More interestingly, direct evidence of contemporary mantle-related methane discharge expanded following EXTREME25 expedition conducted by the Arctic University of Norway (UiT) and the Woods Hole Oceanographic Institution (WHOI) last year.

Deploying the deep-submergence vehicle Aegir 6000 along an exhumed fault scarp of an Oceanic Core Complex in the Fram Strait at depths approaching 2,700 meters, researchers identified an active, low-temperature diffuse fluid discharge area designated the Frigg Vent Field. Using in situ mass spectrometry and the WHOI-developed Sensor for Aqueous Gases in the Environment (SAGE), the team recorded localized, sustained methane and molecular hydrogen anomalies associated with exposed serpentinized peridotites.

Unlike high-temperature hydrothermal black-smoker environments driven by shallow magmatic intrusions, the Fram Strait site turned out to feature fluid venting driven by tectonic detachment faulting that directly exhumes mantle rocks into contact with circulating seawater. Geochemical analysis indicated elevated methane and hydrogen ratios consistent with continuous, low-temperature serpentinization-driven methanogenesis. The experiment finally provided empirical confirmation that modern tectonic windows expose sufficient mantle peridotite to sustain continuous abiotic gas emissions at regional oceanic boundary scales, without requiring sedimentary input.

A concurrent theoretical challenge to the biogenic consensus appeared late last year in Petroleum Science, where researchers re-evaluated the phase equilibrium and reaction kinetics of deep hydrocarbon systems under crustal migration conditions.

The study reviewed laboratory high-pressure multianvil experiments and thermodynamic stability models of C-H-O fluids, proposing that the phase boundary transitions between light alkanes and graphitic or kerogen-like residues are chemically reversible across deep shear zones. The paper argued that the presence of high-molecular-weight polycyclic structures and nitrogen-bearing complexes in deep reservoirs could represent synthetic byproducts of upwardly migrating, de-hydrogenating mantle fluids interacting with transition-metal catalysts, rather than exclusively degraded biological matter.

Furthermore, the authors questioned the absolute diagnostic validity of trace biomarkers (such as nickel and vanadyl porphyrins) within ultra-deep horizons, suggesting that ascending abiotic fluid fronts can extract and concentrate these components from shallow crustal horizons through solvent scavenging. Still, the issue stands that biological steranes and hopanes have never been synthesized abiogenically in yields sufficient to match natural reservoir compositions.

On another front – the debate over field gas provenance has historically depended on isotopic baselines, specifically the carbon (delta-13C) and hydrogen (delta-D) fractionation patterns among methane (C1), ethane (C2), and propane (C3). Abiotic gases were historically categorized by inverse isotopic ordering (delta-13C1 > delta-13C2 > delta-13C3), whereas thermogenic gases display normal isotopic distribution (delta-13C1 < delta-13C2 < delta-13C3).

Hydrothermal alteration experiments published by He et al. (Organic Geochemistry) added further complexity to this diagnostic framework. Their experiments subjected sedimentary organic precursors and pure methane standards to high-pressure hydrogenation in closed gold cells to observe carbon and hydrogen isotopic partitioning across extended thermal regimes.

The resulting datasets showed the following:

1. Extreme thermal over-maturation combined with free hydrogen cracking induces an isotopic rollover in biogenic gases that closely replicates the isotopic reversals previously assumed to be definitive signatures of Fischer-Tropsch-type abiotic reactions.
2. Conversely, the inclusion of iron-rich mineral catalysts in the presence of dissolved inorganic carbon caused abiotic synthesis runs to yield semi-normal fractionation curves under specific kinetic rates.

These experimental results indicate a significant degree of isotopic equifinality. Consequently, isotopic assays alone may no longer be cited as unequivocal proof of either an exclusively biological or an exclusively mantle origin when assessing gases collected from deep, high-temperature drilling targets.

By establishing mechanisms for alkane polymerization in supercritical fluids, demonstrating continuous in situ emissions from exhumed mantle faults, and showing the isotopic convergence between high-temperature biogenic and abiotic reactions, it appears that these studies demonstrate that the physical and chemical processes governing the deep Earth carbon cycle certainly remain more of a mystery than settled science – than we have previously thought to believe, and more research into the permeability, retention capacity, and migration vectors of deep lithospheric fluids must be done to figure out to resolve this new frontline in the old dream of abiogenic hydrocarbons.