The potential for low-temperature abiotic hydrogen generation and a hydrogen-driven deep biosphere

Area of Science:

• Geochemistry
• Astrobiology
• Microbial Ecology

Background:

• Aqueous alteration of olivine releases ferrous iron, driving the formation of molecular hydrogen (H2).
• H2 is a crucial energy source for the deep subsurface biosphere on Earth and potentially on other celestial bodies.
• Understanding H2 generation is vital for assessing the habitability of subsurface environments.

Purpose of the Study:

• To review factors influencing H2 generation potential.
• To focus on conditions relevant to thermophilic and hyperthermophilic microbial life.
• To identify key limitations on H2 production rates.

Main Methods:

• Literature review of factors affecting H2 generation during olivine alteration.
• Analysis of chemical and physical constraints on H2 production.
• Focus on core temperature ranges for extremophilic life.

Main Results:

• Aqueous sulfate can inhibit H2 formation.
• Redox-sensitive carbon and nitrogen compounds have minimal impact at low temperatures.
• H2 generation rate is proportional to olivine dissolution, limited by surface area and water access.
• Water availability and pore/fracture space are primary limiting factors.

Conclusions:

• Early Earth and Mars likely possessed abundant conditions for H2 generation, supporting the emergence of microbial life.
• Factors such as heat flow, olivine abundance, thermodynamic gradients, and reduced atmospheres were favorable.
• The study highlights the importance of geological and hydrological conditions for subsurface habitability.