The Mass Extinction Event that Led to the Reign of The Dinosaurs
The “Kill Mechanism” Similar to Global Warming Today.
Most of us are familiar with the mass extinction event that ended the dinosaurs' reign about 65 million years ago. However, it is less known that an earlier mass extinction event helped the dinosaurs become the dominant group of animals, because it removed most of their natural competitors, including large amphibians. This mass extinction was caused by massive volcanic activity in the central Atlantic Ocean at the end of the Triassic period, about 200 million years ago. In a recent paper Calum Fox from Curtin University in Perth, Australia, and co-authors, provided details on how 70-75 % of all species became extinct at that time .
Mass extinction events are nothing unusual in Earth's natural history. There were even larger ones like the End-Permian extinction 252 million years ago, which led to the extinction of 90-96% of all species at the time. Right now, we are in what is known as the Holocene extinction, which is the result of the expanding human population with its high demand for food and resources. The current extinction rate is much higher compared to the time before humans became the dominant species on our planet. Interestingly, both the End-Triassic and the Holocene mass extinction events are triggered by some of the same chemical agents (mostly an increase of carbon dioxide). This provides us with lessons on how the environment and its ecosystems are impacted, and perhaps what we can do about it.
According to the authors, the rapid degassing of carbon dioxide was caused by a huge uptick in volcanic activity and led to a “two-pronged kill mechanism” at the end of the Triassic period. Enormous amounts of released gas acidified the oceans, which prevented marine life forms (such as mussels and corals) from building the calcium carbonate shells they need for survival. This resulted in major die-offs. Also, major areas in the oceans became euxinic- depleted of oxygen and rich in reduced sulfur compounds. Particularly toxic to marine life was the gas hydrogen sulfide, which is easily recognized by its rotten egg smell. These euxinic zones even extended to the photic zone (the surface layer of the ocean that receives sunlight), where usually most of the biomass is produced. This resulted in even further die-offs.
Massive volcanic outpours and degassing into the central Atlantic Ocean also created hyperthermal climatic events during which global temperatures increased rapidly in a geologically short time. This is not unlike today, as pointed out in a paper led by Gavin Foster from the University of Southampton (UK), who compared today’s global warming with hyperthermal events in Earth's natural history. Both led to acidification and oxygen depletion in the oceans. They suggested that a lot can be learned from these types of events in Earth's past because the consequences to our biosphere are the same whether they are due to natural causes or human-induced activities.
There is, however, one critical difference between the End-Triassic and the Holocene mass extinction. The human-induced activities occur in a much shorter time frame, which provides all species on our planet less time to adapt. Luckily for us, we live in a time with little volcanic activity. One can only imagine what could happen now if huge amounts of volcanic activity in addition to human activity would cause even more global warming: animal and plant life on Earth, including us, would be exposed to a truly two-pronged kill mechanism!