The Last Permian Mass Extinction (LPME) was the largest extinction in Earth’s history to date, killing between 80-90% of life on the planet, although the discovery of definitive evidence of what caused the dramatic changes in climate 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 that ended up in the sediments. in Australia and South Africa. The research has been published in Communication Nature.
Although the LPME occurred more than 250 million years ago, there are similarities to major climate changes occurring today, Frank explains:
“It’s relevant to understanding what might happen on earth in the future. The main cause of climate change is linked to a massive injection of carbon dioxide into the atmosphere at the time of the extinction, which led to rapid warming. »
In the case of LPME, the rapid warming associated with the event is widely believed to be linked to massive volcanism occurring in a huge lava deposit called the Siberian Trap Great Igneous Province (STLIP), Frank says, but direct evidence was still missing.
Volcanoes leave useful clues in the geological record. Along with the lava outpouring, there was also a huge amount of gases released, such as CO2 and methane, as well as particles and heavy metals that have been launched into the atmosphere and deposited around the world.
“However, it’s hard to tie something like this directly to the extinction event,” says Frank. “As geologists, we are looking for some signature – some irrefutable gun – so that 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 this recording still exists.
Frank explains that there is a continuous record of Earth history contained in sediments in marine environments which acts almost like a tape recorder as deposits are quickly buried and protected. These sediments provide an abundance of data on the extinction and how it unfolded in the oceans. On land, it is more difficult to find such well-preserved documents from this period.
To illustrate this, Frank uses Connecticut as an example: the state is rich in metamorphic rocks 400 to 500 million years old at or near the surface, with a cover of glacial deposits dating to around 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’s less of them there,” says Frank.
Not all terrains in the world have such large gaps in the geological record, and previous LPME studies have focused primarily 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 an excellent record of the event, and are areas that Frank and Fielding have studied previously. 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 for samples, hoping to analyze them for mercury isotopes.
Shen was able to analyze the mercury isotopes in the samples and link all the data together, Frank says.
“Volcanic mercury emissions turn out to have a very specific isotopic composition of mercury that has accumulated at the extinction horizon. Knowing the age of these deposits, we can more definitively link the timing of the extinction to this massive eruption in Siberia. The difference with this article is that we examined not only mercury, but also the isotopic composition of mercury from samples in southern high latitudes, both for the first time. »
That definitive timing is something scientists have been working to refine, but as Fielding points out, the more we learn, the more complicated it gets.
“As a starting point, geologists identified the time of the major extinction event at 251.9 million years ago with a high degree of accuracy from radiogenic isotope dating methods. Researchers know that was when the major extinction event happened in the marine environment and it was just assumed that the terrestrial extinction event happened at the same time . »
In Frank and Fielding’s previous research, they found that the extinction event on earth happened 200-600,000 years earlier.
“This suggests that the event itself was not just a big blow 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 does feed into the new findings nicely because it suggests volcanism was the root cause,” says Fielding. “This is only the first impact of the biotic crisis that has happened on earth, and it happened early. It took time to spread across the oceans. The event 251.9 million years ago was the major tipping point for environmental conditions in the deteriorating ocean. for a certain time. »
Tracing the events relies on the knowledge of many different geologists, all of whom specialize in different methods, of sedimentology, geochemistry, paleontology and geochronology, says Frank,
“This type of work requires a lot of collaboration. It all started with fieldwork when a group of us went down 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, which definitely binds the extinction horizon in these land sections which provide a record of what was happening on land due to Siberian trap volcanism . »