END-PERMIAN (250 Ma) - “The Great Dying”
Severity: 1st worst
Cause: Eruption of Siberian Traps
Climate: Cold to extremely warm; ocean acidification and anoxia, ozone destruction
Aftermath: Permanent ecosystem reorganization; low O2 for >106 years
There’s good reason why the End-Permian extinction is referred to as “The Great Dying”; 95% of all marine families, 53% of all marine families, 84% of marine genera, and 70% of known land species went extinct,
The extinction likely occurred in three stages:
1. Land extinctions over ~40,000 yrs
2. Very abrupt marine extinctions
3. Second phase of land extinctions
Calcifying marine organisms such as brachiopods and bryozoa were the hardest hit, representative of ocean acidification. The last of the Cambrian fauna also died off, and this was the only known mass extinction of insects
So what exactly made the End-Permian extinction so severe? There truly was a perfect storm to make this the deadliest million years in Earth’s history.
Earth had been emerging from a moderate ice age when the largest flood basalt event in history (the Siberian Traps) occurred, which released vast amounts of CO2. The oceans then became increasingly warm, acidic, stratified, and euxinic from decaying organic matter. The atmosphere also became flooded with light (biogenically fixed) C, possibly from seafloor methane hydrates or from coal gas released as a result of heating from the Siberian Traps. Greenhouse gases soon caused global temperatures to spike, leading to massive extinction. Global euxinia in the oceans then became a severe problem, with sulfate reducing bacteria releasing large amounts of H2S, poisoning the oceans and atmosphere and thinning the ozone layer. These systems then created a cycle of positive feedbacks:
more die-offs → more euxinia → more H2S → more die-offs.
Marine ecosystems were forever changed after the extinction. Land ecosystems didn’t recover for ~5 My, and O2 levels remained low throughout much of Triassic time.
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