The Late Triassic and earliest Jurassic are characterized as one of the very few times in Earth history where there is no evidence of polar glacial ice sheets. The leading hypothesis is that Earth was in a “greenhouse” state because of very high atmospheric CO2 pressure. Despite modeling results indicating freezing winter temperatures at high latitudes, empirical evidence for freezing has been lacking.
A new study by Rensselaer Polytechnic Institute and Columbia University’s Lamont-Doherty Earth Observatory offers empirical evidence that despite extraordinary high CO2 levels, the temperatures in the Arctic dipped below freezing. The volcanic eruptions in what is referred to as the Central Atlantic Magmatic Province (CAMP) led to short-lived but dramatic volcanic winters amid overall global warming. The volcanic winters lowered the temperature by as much as 18 degrees.
The land animals that survived had feathers or hair as insulation: large dinosaurs. Their survival over non-insulated animals, like prehistoric crocodiles, ushered in the large dinosaurs’ era of dominance.
Morgan Schaller, associate professor of Earth and environmental sciences at Rensselaer Polytechnic Institute, said, “Previously, we had no evidence of the freezing temperatures from this period. The evidence comes from ancient lakes in northern China that had formed at high latitudes during the Triassic Period. There is a unique assemblage of minerals and grains in lake sediments indicative of having been rafted out into deep water by ice.”
“Today, our carbon dioxide level is 420 parts per million. It was anywhere from 1,000 to 4,000 parts per million back then.”
“The eruptions most likely put a bunch of sulfate aerosol in the upper atmosphere. This reflected solar radiation and acted as a driver for cold temperatures.”
“The volcanic winters lasted for decades, which is very fast in geologic terms. Then, they were followed by the opposite extreme.”
“There were creatures living in the tropics that were adapted to warm temperatures and, suddenly, volcanic winters caused it to become very cold. Then, the sulfate collected on rain droplets and formed acid rain. The amount of reflected solar radiation decreased, and temperatures went way up. It got cold fast and then, gradually, became much hotter than it was before the eruptions.”
“All in all, the findings point to the discovery of a rarely observed extinction mechanism. Only creatures that could handle extreme temperatures survived the ETE.”
Curt Breneman, Dean of the Rensselaer School of Science, said, “This insightful analysis carried out by Morgan Schaller and his team shows that if complex animals (such as dinosaurs) had already evolved resilient features that gave them enough time to adapt further as conditions were changing, they could survive extreme climatic and environmental upheavals. These results will not only affect future studies in paleontology but may also inform us about the future of our planet.”