Abiotic nitrogen reduction on the early Earth

Area of Science:

• Geochemistry
• Astrobiology
• Mineralogy

Background:

• Organic precursor production is vital for life's origin.
• Nitrogen (N2) is less efficient for organic synthesis than ammonia.
• Early Earth's reducing conditions were presumed to favor ammonia, but lacked experimental proof.

Purpose of the Study:

• To experimentally investigate mineral-catalyzed nitrogen fixation to ammonia.
• To determine ammonia production feasibility under early Earth crustal and hydrothermal conditions.
• To assess the role of ammonia in resolving the early-faint-Sun paradox.

Main Methods:

• Mineral-catalyzed reduction experiments of N2, NO2-, and NO3- to ammonia.
• Simulated crustal and oceanic hydrothermal system conditions (300–800°C, 0.1–0.4 GPa).
• Analysis of nitrogen species stability at high temperatures (above 800°C).

Main Results:

• Demonstrated mineral-catalyzed ammonia synthesis from N2, NO2-, and NO3- between 300–800°C and 0.1–0.4 GPa.
• Established that only N2 is stable above 800°C, limiting atmospheric ammonia formation during hot accretion.
• Indicated mineral-catalyzed N2 reduction as a potential significant source of ammonia to the Hadean ocean.

Conclusions:

• Mineral-catalyzed N2 reduction likely provided crucial ammonia to the early Hadean ocean.
• Hydrothermal ammonia exchange could have supplied atmospheric ammonia, resolving the early-faint-Sun paradox.
• This research provides experimental support for ammonia's role in prebiotic chemistry and early Earth atmospheric conditions.