The Triassic Period, being the opening page of the Mesozoic Era which spanned from 251 million years ago to about 201 million years ago, is best known for chaperoning the “Age of Dinosaurs” on our planet. Within this period, several of our planet’s extant animal groups appeared and/or flourished; this included the rise of modern-day corals, and the rise of the cynodonts, a clade of therapsids within which all mammals belong and sprung forth from. But what is perhaps the most famous debut during the Triassic is the dawn of the dinosaurs. The appearance of the first dinosaurs in the fossil record are often dated to this period, which include the 231-million-year-old Eoraptor from what is now Argentina.
This brings into question, then, the chain of events that led to the dominance of the dinosaurs that would remain unchallenged for around 166 million years. You see, the geologic time period before the Triassic, known as the Permian Period, was bookended by the Permian Extinction, known as the most severe mass extinction event in Earth’s history. This extinction wiped out around 80% of all marine species at the time and close to 70% of all terrestrial vertebrates species. Reptiles did rise up the occasion to fill the gaps in the ecosystem left behind by those taken by the Permian Extinction, but the first dominant reptiles of this period weren’t actually dinosaurs at all; instead, they were other members of the archosaur family, and were cousins of the dinosaurs. So what happened and took those reptiles away, leaving dinosaurs to take over the world?
The answer would be made clearer with the discovery of a new mass extinction, albeit smaller in scale compared to the massive impact of the previous Permian Extinction, which occurred some 233 million years ago. It would be referred to as the Carnian Pluvial Episode (CPE), and was characterized by what would have been a hot and humid climate paired with substantial rainfall all over the supercontinent Pangaea. This “mega monsoon” period coincided with major changes to the world’s biota; the traces of other archosaurs would diminish after the layer of rock attributed to the CPE; above it, paleontologists would predominantly find dinosaurs, meaning the CPE is key to the dinosaur emergence.
However, this period was also characterized by volcanic eruptions, leading experts to ponder on whether or not one caused the other. Now, research led by the University of Birmingham reveals the true culprit behind the CPE: four distinct events characterized by extreme volcanic activity, which correlates to drastic increases of carbon dioxide (CO2) content in the atmosphere. This study was published in the journal Proceedings of the National Academy of Sciences.
University of Birmingham researchers, including University of Birmingham Professor Jason Hilton, analyzed sediment samples from a lake in Jiyuan Basin, located in northern China. There, they peeked at sediment and plant fossil records. Next, they analyzed these samples obtained using techniques like high-resolution stratigraphy and zircon dating in order to compare the terrestrial conditions within this lakebed to volcanic activity back in North America associated with relatively the same time frame.
In doing so, they found four distinct volcanic episodes, with the volcanism likely originating from the Wrangellia large igneous province, an area hugging the western coast of North America with geologic history of intense volcanic activity dated to around the same time as the CPE. These episodes were said to be linked to a “dramatic increase in global humidity and temperature,” said Hilton.
Each episode disturbed the global carbon cycle from all the CO2 produced by volcanic activity and shifted the climate towards more humid conditions, said Hilton and team. The lakebed in northern China also showed signs of deepening, which coincided with a decrease in oxygen levels and animal life.
Geological data from the same timeframe across the world share a similar story of increased rainfall, causing the proliferation of lakes or swamps in the area. “The climatic changes coincide with a major biological turnover on land that included the ascent of the dinosaurs and the origin of modern conifers.”
Dr. Sarah Greene, also from the University of Birmingham, continued: “Our results show that large volcanic eruptions can occur in multiple, discrete pulses, demonstrating their powerful ability to alter the global carbon cycle, cause climate and hydrological disruption and drive evolutionary processes.”
(For more reading on how volcanoes impacted Earth’s past, check out our pieces on how they may have helped cement the presence of oxygen in our atmosphere, as well as how supervolcanoes may pose a more long-term risk than previously thought.)
References
- Dal Corso, J., Bernardi, M., Sun, Y., Song, H., Seyfullah, L. J., Preto, N., Gianolla, P., Ruffell, A., Kustatscher, E., Roghi, G., Merico, A., Hohn, S., Schmidt, A. R., Marzoli, A., Newton, R. J., Wignall, P. B., & Benton, M. J. (n.d.). Extinction and dawn of the modern world in the Carnian (Late triassic). Science Advances, 6(38), eaba0099. https://doi.org/10.1126/sciadv.aba0099
- Lu, J., Zhang, P., Corso, J. D., Yang, M., Wignall, P. B., Greene, S. E., Shao, L., Lyu, D., & Hilton, J. (2021). Volcanically driven lacustrine ecosystem changes during the Carnian Pluvial Episode (Late triassic). Proceedings of the National Academy of Sciences, 118(40). https://doi.org/10.1073/pnas.2109895118
- Marshall, M. (2019). Did a million years of rain jump-start dinosaur evolution? Nature, 576(7785), 26–28. https://doi.org/10.1038/d41586-019-03699-7
- Sci-News. (2021, September 29). Triassic Volcanic Eruptions Helped Dinosaurs Take Over Earth. Sci-News. http://www.sci-news.com/paleontology/triassic-volcanic-eruptions-10115.html
- University of Bristol. (2020, September 16). Discovery of a new mass extinction – carnian pluvial episode – 233 million years ago. SciTechDaily. https://scitechdaily.com/discovery-of-a-new-mass-extinction-carnian-pluvial-episode-233-million-years-ago/
- Wrangellia oceanic plateau. (n.d.). Retrieved October 14, 2021, from https://www.eoas.ubc.ca/research/wrangellia/background.html
