Most everybody knows that the dinosaurs perished rapidly in a tumultuous extinction, caused by an asteroid strike about 66 million years ago. But it looks like another extinction prior to the appearance of the dinosaurs paved the way for their long reign. That extinction took place about 233 million years ago.
And scientists have only now discovered it.
The extinction took place during what’s called the Carnian Pluvial Episode (CPE). Researchers have examined this period of time before, because they knew the climate changed abruptly then. The climate change was likely caused by copious volcanic activity that created Large Igneous Provinces (LIP). But now a team of researchers have conducted a thorough review of geologic and paleontological evidence from that time and have concluded that a mass extinction took place.
The title of the new research is “Extinction and dawn of the modern world in the Carnian (Late Triassic).” The lead authors are Jacopo Dal Corso of the China University of Geosciences at Wuhan, and Mike Benton of the University of Bristol’s School of Earth Sciences. The new research is published in the journal Science Advances.
Much of the western coast of North America is made up of volcanic basalt. That’s the result of massive volcanic eruptions that created what’s known as the Wrangellia Province. The Wrangellia Province formed in the middle to late Triassic as an oceanic igneous province, and became part of North America in the Late Jurassic or Early Cretaceous.
The authors of the new research say that the eruptions that created Wrangellia also caused severe climate change, and that global warming led to the demise of many of the world’s species, paving the way for the dinosaurs.
“The eruptions peaked in the Carnian,” said Dal Corso in a press release. “I was studying the geochemical signature of the eruptions a few years ago and identified some massive effects on the atmosphere worldwide. The eruptions were so huge, they pumped vast amounts of greenhouse gases like carbon dioxide, and there were spikes of global warming.”
One of the first indications of climate change and extinction during the Carnian was evidence of a prolonged period of increased rainfall. Geologists first discovered this rainfall in the 1980s, and they thought the period lasted about one million years. As the climate changed during that time, it caused a major loss of biodiversity, on land and in the oceans.
As a result of that extinction, coniferous forests expanded, and other, newer types of plant life appeared. The Earth’s ecosystems began to look more like modern-day Earth. But the shift meant a food crisis for existing herbivores.
“The new floras probably provided slim pickings for the surviving herbivorous reptiles,” said Professor Mike Benton. “I had noted a floral switch and ecological catastrophe among the herbivores back in 1983 when I completed my PhD. We now know that dinosaurs originated some 20 million years before this event, but they remained quite rare and unimportant until the Carnian Pluvial Episode hit. It was the sudden arid conditions after the humid episode that gave dinosaurs their chance.”
A bunch of new species appeared at the same time. The Carnian Pluvial Episode didn’t just create space for dinosaurs. The first turtles, crocodiles, lizards, and mammals also appeared. In the oceans, the first coral reefs appeared, as well as many modern plankton groups. The changes in the oceans’ plankton suggest “profound changes in the ocean chemistry and carbonate cycle,” according to the authors.
In their paper they write that “In the sea, the rise of the first scleractinian reefs and rock-forming calcareous nannofossils points to substantial changes in ocean chemistry. On land, there were major diversifications and originations of conifers, insects, dinosaurs, crocodiles, lizards, turtles, and mammals.”
“So far, palaeontologists had identified five “big” mass extinctions in the past 500 million yeas of the history of life,” says Jacopo Dal Corso. “Each of these had a profound effect on the evolution of the Earth and of life. We have identified another great extinction event, and it evidently had a major role in helping to reset life on land and in the oceans, marking the origins of modern ecosystems.”
The changes caused by one million years of rainfall were profound. Terrestrial environments shifted dramatically. Europe became an area dominated by lagoons and freshwater lakes. In other areas around the world, large river systems formed, with abundant freshwater lakes, and extensive deltas and sedimentation. Other “complex palaeoenvironmental system consisting of interlinked inland basins,” formed, according to the authors, in areas like the “North Atlantic rift system, extending from Greenland to Morocco.”
Carbon isotope records show that the Earth’s carbon cycle was subjected to repeated disruptions and perturbations during the CPE. Those same records “indicate repeated injections of 13C-depleted carbon into the ocean-atmosphere system, which may have increased the pCO2 and likely triggered global warming,” the authors write in their paper.
Biodiversity data from fossil records show that many invertebrates suffered elevated extinction rates at the time. Most other marine groups, including gastropods and bivalves, suffered similar extinctions.
Extinctions are depressing, when we think of all the species that have disappeared. They’re gone forever. But extinctions are also about renewal, as this paper shows.
In their summary, the authors write that, “Evidence indicates a possible cascade of events similar to other mass extinctions: LIP eruption as the trigger, release of volcanic gases, rapid shifts in temperature and ?13C, ocean anoxia, and major ecosystem remodeling characterized by both extinctions and diversifications…”
The CPE may have ended the game for many species, but it did herald the appearance of more modern ecosystems, including the expansion of Earth’s coniferous forests. Though extinctions are seen as a kind of setback, they also present new opportunities and niches for new species to exploit. As the paper shows, the dinosaurs only proliferated after the CPE extinction.
The team behind this research is confident that they’ve identified another mass extinction in the data. But they’re more cautious when it comes to the certain cause of it. As they write in their conclusion, “However, because of the lack of precise stratigraphic and geochronological links between Wrangellia and the CPE, we can only speculate on the possible volcanic triggers for the observed extinctions and environmental changes by analogy with other LIP-related events.”
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