Almost everyone knows that the dinosaurs quickly died in a tumultuous extinction caused by an asteroid strike about 66 million years ago. But it looks like another extinction before the appearance of the dinosaurs paved the way for their long reign. This extinction occurred about 233 million years ago.
And scientists have only now discovered it.
The extinction took place during the so-called Carnian Pluvial Episode (CPE). Researchers have already examined this period because they knew that the climate had changed abruptly at that time. Climate change was likely caused by abundant volcanic activity that spawned large Igneous Provinces (LIP). Now a team of researchers has done a thorough review of the geological and paleontological evidence from that period and has concluded that a mass extinction has occurred.
"The eruptions were so big they pumped huge amounts of greenhouse gases like carbon dioxide, and there were spikes in global warming."
Jacopo Dal Corso, co-author, China University of Geosciences
The title of the new research is "Extinction and Beginning of the Modern World in the Carnic (Late Triassic)". The lead authors are Jacopo Dal Corso from the China University of Geosciences in Wuhan and Mike Benton from the School of Earth Sciences at the University of Bristol. The new research is published in the journal Science Advances.
Much of the west coast of North America is made up of volcanic basalt. This is the result of massive volcanic eruptions that spawned what is known as Wrangellia Province. Wrangellia Province formed as an oceanic igneous province in the Middle to Late Triassic and became part of North America in the Late Jurassic or Early Cretaceous Period.
Wrangellia is an arc terrane on the North American west coast that stretches from Vancouver Island to central Alaska. Highlighted here is Southern Wrangellia, also known as Wrangell. Photo credits: By Fama Clamosa – own work, created with the Gplates and data sets listed below., CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=85176529
The authors of the new study say the outbreaks that caused Wrangellia also caused severe climate change and that global warming resulted in the deaths of many species in the world and paved the way for the dinosaurs.
"The eruptions peaked in Carnic," Dal Corso said in a press release. “I examined the geochemical signature of the eruptions a few years ago and found some massive effects on the atmosphere around the world. The eruptions were so big they pumped huge amounts of greenhouse gases like carbon dioxide, and there were spikes in global warming. "
A partially geological time scale of the earth. Downstairs is older, upstairs is younger. The Triassic began around 252 mya with the Induan Age. The Cretaceous Period ended about 72 mya at the end of the Maastricht Age. Wrangell Province formed in the mid-Late Triassic and joined North America in the Late Jurassic or Early Cretaceous Period. Photo credit: Wikipedia
One of the first signs of climate change and extinction during Carnival was evidence of a prolonged period of increased rainfall. Geologists first discovered this precipitation in the 1980s and believed the period lasted about a million years. When the climate changed during this period, it caused a great loss of biodiversity on land and in the oceans.
As a result of this extinction, coniferous forests expanded and other, newer species of plants appeared. The earth's ecosystems looked more like the modern earth. But the shift meant a food crisis for existing herbivores.
"The new floras likely provided a slim harvest for the surviving herbivorous reptiles," said Professor Mike Benton. “In 1983, when I was completing my doctoral thesis, I noticed a change of flowers and an ecological catastrophe among herbivores. We now know that dinosaurs formed about 20 million years before this event, but they remained fairly rare and unimportant until the Carnian Pluvial episode hit. It was the sudden dry conditions after the wet episode that gave the dinosaurs their chance. "
This is a photo of the Nikolai Formation along Glacier Creek in the Wrangell Mountains, Alaska. It is part of the Wrangellis Igneous province and has an approximately 1000 meter high deposit of basaltic lava. The yellow line shows the top of the basalt with a limestone formation above it. The volcanic activity that created this basalt also caused the climate to change rapidly, causing a longer period of rain, the Carnian Pluvial Event. This event triggered a mass extinction. Photo credit: Greene et al., 2008.
At the same time, a number of new species appeared. The Carnian Pluvial episode didn't just make room for dinosaurs. The first turtles, crocodiles, lizards and mammals also appeared. The first coral reefs and many modern groups of plankton appeared in the oceans. According to the authors, the changes in the plankton of the oceans indicate “profound changes in the chemistry of the oceans and in the carbonate cycle”.
In their work they write: “In the sea, the rise of the first scleractinic reefs and rock-forming calcareous nannofossils indicate significant changes in the chemistry of the oceans. On land, there were great differences and origins from conifers, insects, dinosaurs, crocodiles, lizards, turtles and mammals. "
Summary of major extinction events over time, highlighting the new Carnian Pluvial episode 233 million years ago. Photo credits: © D. Bonadonna / MUSE, Trento.
“So far, paleontologists have identified five“ major ”mass extinctions in the last 500 million years of life,” says Jacopo Dal Corso. “Each of these had a profound influence on the development of the earth and life. We have identified another major extinction that appears to have been instrumental in resetting life on land and in the oceans and marking the origins of modern ecosystems. "
Part of one of the characters from the study. It shows the Carnian Pluvial episode in yellow and the explosion of dinosaur species is marked with the red star.
The changes caused by a million years of rainfall have been profound. The terrestrial environments have changed dramatically. Europe became an area dominated by lagoons and freshwater lakes. In other areas of the world, large river systems with abundant freshwater lakes and extensive deltas and sedimentation formed. Other "complex paleoenvironmental systems consisting of interconnected inland basins" formed, according to the authors, in areas such as the "North Atlantic Rift System, which extends from Greenland to Morocco".
Records of carbon isotopes show that the earth's carbon cycle was exposed to repeated perturbations and disturbances during CPE. The same recordings suggest repeated injections of 13C-depleted carbon into the ocean-atmosphere system, which may have increased pCO2 and likely triggered global warming, the authors write in their paper.
Biodiversity data from fossil holdings shows that many invertebrates had an increased rate of extinction at the time. Most of the other marine groups, including gastropods and mussels, were similarly critically endangered.
This figure from the study shows the decline in marine groups during the Carnian Pluvial Event. Photo credit: Dal Corse et al 2020.
Extinction is depressing when we think of all the species that have disappeared. You are gone forever. But extinction is also about renewal, as this paper shows.
In their abstract, the authors write: “There are indications of a possible cascade of events that are similar to other mass extinctions: LIP eruption as a trigger, release of volcanic gases, rapid temperature shifts and 13 ° C, ocean anoxia and ecosystem reshaping both characterized by extinction as well as through diversification … "
The CPE may have finished the game for many species, but it heralded the appearance of more modern ecosystems, including the expansion of the earth's coniferous forests. While extinction is seen as a kind of setback, it also opens up new opportunities and niches for new species. As the paper shows, the dinosaurs did not reproduce until after the CPE became extinct.
The team behind this research is confident that they identified another mass extinction in the data. But they are more careful when it comes to the specific cause. In their conclusion they write: “Due to the lack of precise stratigraphic and geochronological connections between Wrangellia and the CPE, however, we can only speculate about the possible volcanic triggers for the observed extinctions and environmental changes by analogy with other LIP-related events. ”