A productivity collapse to end Earth's Great Oxidation

Area of Science:

• Geochemistry
• Paleoclimatology
• Earth Science

Background:

• The Great Oxidation Event (GOE) (2.4–2.05 billion years ago) may have led to decreased biosphere size or carbon export efficiency.
• The precise timing, tempo, and triggers for this potential decline remain unclear.

Purpose of the Study:

• To investigate the hypothesis of a post-GOE biosphere reduction.
• To constrain the timing and nature of changes in Earth's biosphere following the GOE.

Main Methods:

• Analysis of sulfate mineral isotope geochemistry (sulfur, barium, and triple-oxygen isotopes) from the Belcher Group, Canada.
• Radiometric dating of surrounding rock strata to establish a precise timeline.

Main Results:

• Sulfate minerals dated to approximately 2,018 Ma, shortly after the GOE, exhibit negative triple-oxygen isotope anomalies (as low as -0.8‰).
• These anomalies indicate a rapid primary productivity decline exceeding 80% in the aftermath of the GOE.
• The data suggest a collapse in primary productivity, not export efficiency, pointing to nutrient limitation.

Conclusions:

• Earth's biosphere experienced a significant, geologically unprecedented reduction in size at the end of the GOE.
• A shift in nutrient availability, likely phosphorus, triggered this collapse in primary productivity.
• The end of the GOE marked a transition from "feast" to "famine" for Earth's biosphere.