Researchers in the Department of Geoscience have taken a look back — way back — to shed new light on how geological events 252 million years ago may hold clues to the forces shaping our planet today and into the future.
Professor Charles Henderson and postdoctoral fellow Shane Schoepfer are co-authors on a paper published last week in the Proceedings of the National Academy of Sciences examining sediment samples from the Panthalassic Ocean floor. Their findings show that an abundance of hydrogen sulfide (H2S) gas arose in the Panthalassic Ocean due to sudden global warming at the end of the Permian geologic period, causing the planet’s oceans to become toxic. While the culprit of climate change at that time was massive volcanic eruptions in Siberia, modern-day global warming may be leading to similar events in the oceans of today.
Ancient sea floor sediment key to understanding mass extinction event
Some 335 million years ago, the Earth’s continents assembled into one supercontinent called Pangea, which was surrounded by the Panthalassic Ocean. “In Permian times, that ocean would have made up the majority of the planet,” explains Schoepfer. “However, there’s very little of that sea floor left. Most of it has been subducted under the continents and recycled back into the earth, so not many records of it survive.”
There were, however, two significant sites where Schoepfer, Henderson, and their co-authors were able to locate and analyze sediment from the ancient ocean: in Japan, where deep sea sediments were accreted onto land by tectonic plate movements, and at the Opal Creek site in Kananaskis Country, Alberta, which is becoming one of the most studied sites in the world. The Opal Creek section was located along the subtropical coast of what would become North America.
Understanding the geochemical conditions of the Panthalassic Ocean is important to understanding the Earth’s environment during the times leading up to the Permian-Triassic (or end-Permian) mass extinction. This event was the most severe extinction in the history of life on earth, and is assumed to have killed off more than 90 per cent of the existing marine species. Schoepfer and Henderson say that sporadic bursts of toxic H2S gas in the oceans may have continued to occur for five million years after the mass extinction, impeding the ability of many marine species to repopulate.
Toxic gases in oceans likely delayed recovery of marine life after end-Permian mass extinction
To determine Earth’s conditions at the time of the end-Permian extinction, the team examined the rock samples from the Japanese and Opal Creek sites and looked at multiple isotopes of sulfur in the mineral pyrite. Pyrite forms in marine waters and sediments where there is no oxygen, which allows bacteria to produce H2S.
Their results showed that free H2S in the water was common throughout the Panthalassic Ocean. Using a novel technique pioneered by the study’s primary author, Yanan Shen of the School of Earth and Space Sciences, University of Science and Technology of China, that measured multiple sulfur isotopes, the group found that toxic deep waters seem to have welled up to the surface many times during and after the end-Permian extinction. This may be what is directly responsible for killing so many marine organisms and for delaying the recovery for millions of years.
“Sporadic upwellings of toxic ocean water may have been going on for about five million years after the end-Permian mass extinction, which would have really delayed recovery,” says Henderson. “It’s about five million years before we find evidence of similar biodiversity and ecosystem health that we saw before the extinction.”
Loss of oxygen in oceans can signal changes in Earth’s climate
The study helps bring deeper understanding of how the oceans respond to intense global warming. “We are already seeing the effects of losing dissolved oxygen in some coastal environments, where too many nutrients are running off into the water,” Schoepfer says. “Modern-day global warming might also be affecting oxygen levels in the Pacific Ocean. The increasing prevalence of El Niño years and the warm-water ‘blob’ in the Pacific may be early signs of weakened cold-water upwelling, similar to what we have suggested based on our earlier studies at Opal Creek.”
While the aforementioned volcanic action in Siberia is the likely culprit of the climate change that precipitated the end-Permian extinction, Henderson says the geological findings from the Permian period may have some relevance to the forces shaping Earth in modern times. “Every day, all around the world, there is volcanic activity on the Earth’s surface and along our mid-ocean ridges. These are normal things, but problems arise when they happen at really high rates, and different effects come together at the same time.”
“We don’t know exactly what’s going to happen. An advantage of looking at the rock record is seeing something that has been completely played through — the experiment is complete. The big questions today are how things are going to change, how quickly life can adapt to climate change, and are there going to be any other kinds of dynamics that will reverse or buffer to some extent.
"The rock record is cryptic, but it records what has already happened. You’ve just got to find ways to get the story out.”
This study was supported by the National Natural Science Foundation of China, the American National Science Foundation, and NSERC.