Oxygen depletion played a role in late Triassic mass extinction



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Over 201 million years ago, lifeforms in late Triassic period faced a great change, causing the fourth known mass extinction which eliminated more than 70% of species existing at that time.

Top ocean surfaces became devoid of oxygen and sulfidic, a condition scientists referred to as ‘marine photic zone euxinia’. Hydrogen sulphide, the by-product of microorganisms that thrived in anoxic conditions, is known to be toxic to most other organisms. This phenomenon was observed in the region of Panthalassic Ocean, one of the two oceans which surrounded the supercontinent of Pangaea.

On the Queen Charlotte Islands, off the coast of British Columbia, Canada, traces of Panthalassic organic materials showed evidences of sulphur bacteria, indicating the severe depletion of oxygen in the open oceans. While previous studies have reported evidences of euxenia from shallow and coastal environments, the latest findings indicated a change that happened on a global level.

According to Professor Jessica Whiteside of the University of Southampton, the breaking up of Pangaea caused volcanic rifts which spewed carbon dioxide into the atmosphere. The greenhouse gas raised the temperatures, triggering changes in ocean circulation, acidification, and deoxygenation. This change of chemical composition in the waters is also thought to have changed the flow of nutrients, disrupting the oceanic food chains.

The chemical changes on land also triggered a mass extinction event, killing most therapsids, amphibians, and non-dinosaurian archosaurs, which allowed dinosaurs to dominate the preceding period of Jurassic. This study about the climate change of the past also provides us an insight on the possible outcomes of the global-scale carbon dioxide crisis we are facing in the present day.