Examining the molecules left in the geological sediments of northern Italy indicates that wildfires caused by volcanic activity may have contributed to the end-Triassic mass extinction event.
Researchers from Khalifa University have examined geological sediments in northern Italy to better understand the wildfire events that occurred at the start of one of Earth’s major extinction events. Dr. Calum Fox, Postdoctoral Fellow, and Dr. Aisha Al Suwaidi, Associate Professor, collaborated with researchers from Curtin University and Universita degli Studi di Padova, Italy, to use records of molecules left behind from wildfire to report the best evidence so far of wildfire activity at the end of the Triassic Period. The researchers found an intense and short-lived wildfire event that linked terrestrial and marine ecosystem stress that precipitated the extinction event.
They published their results in Global and Planetary Change.
Earth’s history is punctuated by major extinction events. One such period, bookended by extinctions, is the Triassic Period: the age of the rise of the dinosaurs.
The Triassic Period (252-201 million years ago) began after one such extinction event and ended with another, with elements of climate change that also occur today. By the end of the Triassic Period, sea levels were rising and the oceans became more acidic, which contributed to dramatic extinctions in the oceans.
“The end-Triassic mass extinction event was driven by a massive input of carbon dioxide and other harmful volatiles from Earth’s most extensive volcano networks at the time,” Dr. Fox said. “Although still not completely understood, there’s evidence to suggest that combinations of acidification and anoxia are important mechanisms of marine extinction. By contrast, the mechanisms responsible for the loss of life on land have received much less attention than those for the marine extinction at the end of the Triassic Period.”
Known as the Central Atlantic Magmatic Province (CAMP), the area that is now the Atlantic Ocean experienced mass volcanic activity that doubled or even tripled the amount of paleoatmospheric carbon dioxide at the time. This is expected to have led to “a series of cascading environmental catastrophes” resulting in the end-Triassic mass extinction event (ETE).
Recent research has determined that these volcanic eruptions occurred at the start of the extinction period, but the CAMP is also expected to have driven intensive wildfire activity at the end of this period.
Wildfires are evidenced by polycyclic aromatic hydrocarbons (PAH), a class of chemicals that occurs naturally in coal and oil deposits. They result from burning organic matter, such as in forest fires.
High levels of PAH were found in rocks dating from the end of the Cretaceous Period, the geological period following the Jurassic, likely from the mass extinction event that wiped out the dinosaurs. More than 100 times the level of PAH was found in rocks from this time frame, compared with other periods, with this spike attributed to massive fires that consumed about 20 percent of the terrestrial biomass in a very short time.
“Increases in PAHs that can form from incomplete combustion are commonly used as evidence of wildfire activity across the end-Triassic mass extinction event and other periods of volcanic activity-driven global warming,” Dr. Fox said. “However, these PAHs can have other sources and also represent processes unrelated to fire events, including volcanic and hydrothermal vent activities, meteorites and soil erosion.”
To better determine the wildfire and soil erosion records from the ETE, the research team investigated the low molecular-weight (LMW) and high molecular-weight (HMW) PAH compounds found in the Lombardy Basin in northern Italy. They compared their findings to PAH records reported from globally dispersed sites.
“LMW PAHs are attributed to processors other than fire, such as soil erosion and markers of ecosystem collapse that are crucial to better understanding ETE ecological perturbations,” Dr. Fox said. “PAHs with a heavier molecular weight are frequently attributed to wildfire events but are not exclusively derived from combustion. However, we interpret the abundance of HMW compared to LMW PAH to represent the intensity of wildfire burning, due to higher temperature fire events producing greater quantities of PAHs. High abundances of these PAHs could indicate that higher intensity burn events occurred close to where the PAHs were found.”
By examining the different sizes of PAH molecules, the researchers determined that the geological record in the Lombardy Basin supports a short-lived but more intense wildfire event at the time thought to represent the onset of the extinction event. Further analysis comparing the Lombardy record to global records also shows evidence of intense wildfire activity at this time.
“This provides evidence of likely CAMP-driven widespread wildfire activity across multiple basins surrounding the time of the end-Triassic mass extinction event that were important for terrestrial ecosystem perturbations, but such studies require further investigations to determine the full fire history of the ETE,” Dr. Fox said.
There’s a lot of history between the end of the Triassic Period 201 million years ago and the 21st century experience of climate change but similarities exist. Insights to the causes of past major extinction events can help understand the current issues facing modern ecosystems and environments. As carbon dioxide levels continue to increase, understanding the geological events of history will help predict what climate changes we can expect in the future.
15 November 2022