(CN) – Researchers have discovered new evidence adding to the idea that the mass extinction of dinosaurs was brought on by an asteroid striking Earth rather than the volcanic activity ravaging the surface.
In a study published Thursday in the journal Science, researchers analyzed well-preserved ocean drilling and global temperature records to evaluate the impact of greenhouse outgassing by volcanic eruptions millions of years ago. The team hoped to measure the effect this volcanism in the Deccan Traps had on temperatures worldwide. What they found shows that volcanic gases played a big role in supporting the rise and success of different species after the extinction, rather than causing the mass die-off.
Across what is now west-central India, Earth’s surface was split open by countless volcanic seams that released large amounts of lava. These eruptions of lava and gases, known as the Deccan Traps, would have spread to areas roughly the size of Texas. Previous studies show Earth’s temperature had gradually increased by around 9 degrees Fahrenheit before the extinction event, leading some to believe the precarious Deccan Traps played a role in this climate change.
Another study concluded that these volcanoes erupted in four large pulses rather than continuously, with only one pulse right before the asteroid impact, making it plausible that the first pulse contributed to the extinction of 60% of life on Earth. Also, in the same way that volcanoes today release streams of carbon dioxide even while dormant, the Deccan Traps could have released such great amounts that the global temperature increased and the ocean became too acidic to support most life.
Just before the Cretaceous-Paleogene (K/Pg) mass extinction 66 million years ago, this extreme volcanism posed a great threat to the surface-dwellers that roamed Earth. At the same time of this large-scale volcanism, the planet also faced a catastrophic asteroid impact and the long reign of the dinosaurs came to an end.
To this day, scientists debate about whether the release of gases was the smoking gun that brought on the famous extinction, but the timing was so intertwined with the asteroid event that the two have yet to be disentangled. Understanding the effect of such great amounts of lava from the Deccan traps and the asteroid impact on the mass extinction has been challenging to say the least.
“This debate has been going on for nearly 40 years, but in the past 20 years people have been more in favor of the asteroid impact causing the mass extinction. New evidence in the past 5 years however has been discovered about the Deccan Traps that reignited the debate, and the traps are actually more closely restrained to the time period when the impact occurred,” Hull said in an email.
This study stands out from similar studies of the past, however. While previous research on this topic focused mainly on the accumulation of lava released, Hull and the team took a different approach. They evaluated the much more environmentally relevant aspect of the volcanic eruption that is outgassing.
“Those studies looked at the age of the lava due to the available tools and data techniques at the time, though they did say they wanted to look at outgassing. What our study did was instead of trying to get the age of the lava, we used it in our hypothesis of what may have happened to trace outgassing in relation to global temperature and traces of carbon cycle,” Hull said.
When a volcano erupts, it releases a plethora of gases, including carbon dioxide, sulfur, hydrogen sulfide, hydrogen chloride, hydrogen fluoride and traces of many others. Hull and the team designed multiple models of several different scenarios to investigate the effects of carbon dioxide and sulfur emissions on long-term global temperatures.
They were able to analyze the timing of Deccan outgassing by comparing the results to global paleotemperature records spanning the K/Pg extinction event. The results from this study show that at least 50% or more of the major Deccan outgassing took place long before the asteroid impact, not just before it.
“People don’t realize that the tech we use to tell the age of rocks and the age of earth is improving rapidly, and our ability to figure out when things happen is improving as well. When things happen 66.2 or 66.15 million years ago, it seems like a decimal point to us but for the organisms it can be hundreds or thousands of years,” Hull said.
The authors conclude this evidence proves that although Earth’s climate underwent drastic change before the asteroid’s arrival, only the impact coincided with the mass extinction event and volcanoes weren’t to blame. Instead, the authors propose that the timing of this outgassing would instead have brought on changes in the carbon cycle that would allow the ocean to absorb massive quantities of the released carbon dioxide. This would have had the effect of limiting the global warming that would have otherwise been expected from post-extinction Deccan volcanism, and promoted the rise of new life.
“Volcanism may have played a role post-extinction. After an extinction, it takes a long time for an ecosystem to have the same function – it could take half a million to a million years for organisms to re-evolvle. The focus then has to do with the time it takes for ecosystems to reassemble, and shows that volcanism can play a role, and this study leaves both options open,” Hull said.