A new model for atmospheric oxygen over Phanerozoic time

Area of Science:

• Geochemistry
• Paleoclimatology
• Sedimentary Geology

Background:

• Atmospheric oxygen (O2) levels have varied throughout Earth's history.
• Understanding these variations is crucial for reconstructing past environments and life.
• Previous models have explored factors influencing O2, but a comprehensive approach is needed.

Purpose of the Study:

• To develop a mathematical model for calculating atmospheric O2 levels over the past 570 million years.
• To investigate the roles of organic carbon (C) and pyrite sulfur (S) burial and weathering in O2 regulation.
• To determine the primary drivers of Phanerozoic O2 fluctuations.

Main Methods:

• Constructed a mathematical model based on burial and weathering rates of organic carbon and pyrite sulfur.
• Calculated burial rates using assumed constant clastic sedimentation rates and rock type compositions (sandstones, shales, coal basins, red beds).
• Incorporated negative feedback mechanisms, such as higher weathering rates for younger rocks, to stabilize the model.

Main Results:

• Atmospheric O2 levels have varied considerably over Phanerozoic time.
• Elevated O2 occurred during the Late Carboniferous and Permian due to extensive organic matter burial in coal swamps.
• A significant O2 decrease in the Late Permian was linked to the decline of coal swamps and increased deposition of C- and S-free red beds.

Conclusions:

• Sediment redistribution among different rock types, rather than total sedimentation rate, is the key factor controlling atmospheric O2.
• The rise and fall of coal swamps played a critical role in major O2 fluctuations.
• Sedimentation is identified as the dominant driver of Phanerozoic O2 level changes, outweighing weathering or high-temperature geological processes.