Hydrogen consumption by methanogens on the early Earth

Area of Science:

• Astrobiology and Early Life Research
• Biogeochemistry and Geomicrobiology

Background:

• The origin of life may have involved chemosynthesis rather than photosynthesis.
• Early Earth's primary production could have relied on available chemical energy sources.
• Abiotic organic material depletion necessitated alternative energy pathways for early life.

Purpose of the Study:

• To investigate the potential of chemical energy for early life's primary production.
• To determine the viability of hydrogen (H2) as an electron donor for early chemoautotrophs.
• To assess the role of methanogens in consuming H2 and influencing early atmospheric chemistry.

Main Methods:

• Culturing methanogens with carbon dioxide (CO2) as the sole carbon source.
• Measuring hydrogen (H2) consumption rates at low partial pressures (down to 4 Pa).
• Comparing experimental H2 growth limits with field data from deep basalt aquifers.

Main Results:

• Certain methanogens efficiently consume H2 down to 4 Pa partial pressure.
• Growth is sustained with CO2 as the sole carbon source at a rate of 0.7 ng H2 min-1 microgram-1 cell protein.
• Observed H2 growth limits align with those found in natural deep-earth environments.

Conclusions:

• Chemoautotrophy utilizing H2 and CO2 was a plausible primary production pathway for early life.
• H2-consuming autotrophs likely played a significant role in regulating early Earth's atmosphere.
• These organisms represent a major sink for H2, competing with atmospheric escape.