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How could oceanic anoxia have caused the Permian extinction?
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Permian extinction
The diversity of marine animal families since late Precambrian time. The data for the curve comprise only those families that are reliably preserved in the fossil record; the 1,900 value for living families also includes those families rarely preserved as fossils. The several pronounced dips in the curve correspond to major mass-extinction events. The most catastrophic extinction took place at the end of the Permian Period.
Oceanic anoxia—the condition of having very low levels of dissolved oxygen in seawater—is considered a significant factor in the Permian extinction, as it likely disrupted essential biological cycles.1
Scientists associate this widespread anoxia with the prolonged eruption of the Siberian flood basalts. These volcanic events likely contributed to the extinction in several ways:1
- Atmospheric Changes: The eruptions injected massive amounts of carbon dioxide into the atmosphere, leading to significant climate shifts.1
- Inhibition of Photosynthesis: Volcanic ash clouds may have restricted the sunlight necessary for photosynthesis, which inhibited carbon fixation by plants and reduced the extraction of carbon dioxide from the atmosphere.1
- Carbon Cycle Disruption: The resulting environmental stress, combined with the potential burning of coal seams and forests, altered the carbon cycle. This is evidenced by unusually high amounts of the carbon isotope C found in Permian sediments, which researchers link to the development of anoxic conditions in the oceans.1
These cumulative ecological pressures severely reduced the diversity of marine life, particularly affecting shallow-water invertebrates.12