The Last Permian Mass Extinction (LPME) was the largest extinction event in Earth’s history to date, killing between 80 and 90% of life on the planet, although discovering definitive evidence of what caused the dramatic climate changes has eluded experts.
An international team of scientists, including Professor and Head of Department Tracy Frank and Professor Christopher Fielding, researchers from UConn’s Department of Earth Sciences, are working to understand the cause and timing of LPME events by focusing on mercury from Siberian volcanoes concentrate that in the sediments. in Australia and South Africa. The research was published in Nature Communication.
Although the LPME occurred more than 250 million years ago, there are similarities to major climate changes happening today, Frank explains:
“It is relevant for understanding what could happen on Earth in the future. The main cause of climate change is associated with a massive injection of carbon dioxide into the atmosphere at the time of the extinction, leading to rapid warming. »
In the case of LPME, the rapid warming associated with the event is widely believed to be related to massive volcanism occurring in a giant lava deposit called the Siberian Trap Great Igneous Province (STLIP), Frank says, but direct evidence was still lacking.
Volcanoes leave useful clues in the geological record. The lava eruption also released a tremendous amount of gases, such as CO2 and methane, as well as particles and heavy metals, which were thrown into the atmosphere and deposited around the world.
“However, it is difficult to directly link something like this to the extinction event,” says Frank. “As geologists, we’re looking for a signature — an irrefutable weapon — so we can absolutely pinpoint the cause. »
In this case, the compelling evidence the researchers focused on was mercury, one of the heavy metals associated with volcanic eruptions. The trick is to find areas where that record still exists.
Frank explains that sediments in marine environments hold a continuous record of Earth’s history that works almost like a tape recorder as debris is quickly buried and protected. These sediments provide a wealth of data about the extinction event and how it unfolded in the oceans. It is more difficult to find such well-preserved documents from this period on land.
To illustrate this, Frank uses Connecticut as an example: The state is rich in metamorphic rocks that are 400 to 500 million years old at or near the surface, with a cover of glacial deposits that are about 23,000 years old.
“There is a big gap in the records here. You have to be lucky to keep the Earth records, and that’s why they’re not as well studied because there are fewer of them there,” says Frank.
Not all areas of the world have such large gaps in the geological record, and previous LPME studies have primarily focused on sites found in the northern hemisphere. However, the Sydney Basin in eastern Australia and the Karoo Basin in South Africa are two areas in the southern hemisphere that have excellent records of the event and are areas that Frank and Fielding have previously studied. A colleague and co-author, Jun Shen of the State Key Laboratory of Geological Processes and Mineral Resources at the University of Geosciences of China contacted and contacted Frank, Fielding and other co-authors to obtain samples in hopes of using them on analyze mercury isotopes.
Shen was able to analyze the mercury isotopes in the samples and tie all the data together, says Frank.
“It turns out that volcanic mercury emissions have a very specific isotopic composition of mercury accumulated at the extinction horizon. If we know the age of these deposits, we can more definitively link the timing of the extinction to this massive eruption in Siberia. The difference from this article is that for the first time we have examined not only mercury but also the isotopic composition of mercury from samples taken at southern high latitudes. »
Scientists have been working to refine this ultimate timing, but as Fielding points out, the more we learn, the more complicated it gets.
“As a starting point, geologists have determined the timing of the great extinction event 251.9 million years ago with high accuracy using radiogenic isotope dating methods. Researchers know that this was when the great marine extinction event took place, and it was simply assumed that the terrestrial extinction event happened at the same time. »
In Frank and Fielding’s earlier research, they found that extinctions on Earth occurred 200-600,000 years earlier.
“This suggests that the event itself was not just a big hit that happened instantly. It wasn’t just a really bad day on Earth, so to speak, it took a while to build up, and that translates well into the new findings because it suggests volcanism was the main cause,” says Fielding. “This is just the first impact of the biotic crisis that has occurred on Earth, and it happened early. It took time to spread across the oceans. The event, 251.9 million years ago, was the major turning point for environmental conditions in the deteriorating ocean. for a certain time. »
Tracking events relies on the knowledge of many different geologists, each specializing in different methods of sedimentology, geochemistry, paleontology and geochronology, says Frank.
“This kind of work requires a lot of collaboration. It all started with fieldwork when a group of us went to Australia where we studied the stratigraphic sections that preserved the time interval in question. The main point is that we now have a signature in the form of isotopic signatures of mercury definitively tying the extinction horizon in these stretches of land that provide a record of what happened on land due to Siberian trap volcanism. »