Date:

Did volcanoes kill the dinosaurs? New evidence points to ‘maybe.’

Fact: About 66 million years ago, at the end of the Cretaceous period, 75 percent of plant and animal species went extinct, including the dinosaurs (except those that evolved into birds).

Fact: About 66 million years ago, an enormous asteroid or comet hit the Earth near what is now Chicxulub, Mexico, throwing rock, dust and water vapor into the atmosphere.

- Advertisement -

Fact: About 66 million years ago, a massive volcano erupted lavas in India that are now called the Deccan Traps, burying much of the subcontinent under more than 11,000 feet of basalt (lava rock) and pouring poisonous gases into the atmosphere.

Princeton geoscientists Blair Schoene and Gerta Keller led an international team of researchers who have assembled the first high-resolution timeline for the eruptions in India’s Deccan Traps. Their research appears in the Feb. 22 issue of the journal Science.

“Everyone has heard that the dinosaurs died from an asteroid hitting the Earth,” said Schoene, an associate professor of geosciences. “What many people don’t realize is that there have been many other mass extinctions in the last 500 million years, and many of them coincide with large volcanic outpourings” from the massive volcanoes known as flood basalts or large igneous provinces.

Keller, a professor of geosciences, has argued for decades that the eruption of the Deccan Traps caused the dinosaur mass extinction. In 2013, she, Schoene, and his students began trying to find the ages of the thick layers of lava, which were known to be about the right age but had never been precisely dated.

- Advertisement -

Schoene uses several techniques for geochronology, the science of assigning ages to rocks. The most famous geochronology technique, usually called “carbon dating,” uses the decay rate of radioactive carbon-14 to find fossils ages. That works for plants or animals that are a few thousand years old, making it useful for archaeology but not for 66-million-year-old basalt. For rocks from around the time of the mass extinction, geoscientists have a few choices of naturally radioactive materials. Uranium-lead geochronology yields very precise ages, but minerals containing uranium rarely occur in basalt, the rock that makes up the massive lava flows; uranium-bearing zircon is more often found in explosive eruptions from Mount St. Helens-type volcanoes, which have a more silica-rich chemistry.

The researchers were aware that the odds were stacked against them. “I don’t think that any of us anticipated that our first trip to the Deccan Traps would lead to the type of dataset that we were able to produce,” said Mike Eddy of the Class of 2011, now a postdoctoral research associate in geosciences and a co-author on the Science paper.

For the first few days, the researchers gathered samples of coarse-grained basalts, trying unsuccessfully to find uranium-bearing minerals. Then came a stroke of luck.

“During our first week in India, we found a high-silica ash bed between two basalt flows, and it got our gears turning,” Eddy said. The researchers knew that silica-rich volcanic ash could easily contain the tiny zircon crystals that preserve radioactive uranium. “The real breakthrough came a day or two later, when Blair realized that the fossil soils may have also collected this type of ash in small amounts,” Eddy said.

In other words, instead of focusing on the lava flows themselves, the researchers shifted their focus to the zircon crystals found in the layers of ash in soil between the lava beds. By precisely dating zircons that were deposited before and after the Deccan Traps lava flows, they could tightly constrain when the volcano must have erupted.

Over three field seasons, the researchers gathered samples from more than a hundred sites and shipped them back to the lab at Princeton. “It is always entertaining when we ship samples at the end of the trip,” said Eddy. “This frequently involves a full day, starting with finding cardboard boxes that have enough structural integrity to make it back to the USA, packing said boxes, a visit to the post office to pick up the necessary forms and have the boxes inspected, a visit to a cloth shop to buy canvas, a visit to a tailor to have the boxes sewn into canvas bags, traveling around town to numerous ATMs to collect enough cash to ship the boxes internationally, and a final few hours of paperwork and stamps to get the boxes out the door. In total, the entire process can take up to 12 hours.”

Of the 141 sample sites, 24 yielded uranium-bearing zircon crystals, which allowed the research team to conclude that the Deccan Traps erupted in four distinct pulses, each time belching enormous volumes of sulfur and carbon dioxide into the atmosphere. The thousands of tons of lava would have killed anything living nearby, but the gases reached around the world.

Sulfurous gases can cool the atmosphere in the short term, while carbon dioxide warms it in the long term. When volcanoes release enormous volumes of both, “these can lead to climate swings between warm and cold periods that make it really hard for life on Earth,” said Schoene. To determine how big an effect it would have had, they needed to constrain the timing of the eruptions: Tons of carbon dioxide erupted in a hundred years will have very different effects than the same volume outgassed over the course of a million years.

Of the four eruption pulses, two took place before the mass extinctions, with the second beginning only tens of thousands of years before the Chicxulub impact — a geologically short amount of time. “The first two pulses … correspond with a period of time where climate fluctuated from cold to hot to cold again, and many scientists think this indicated an initial disruption to the climate that may have contributed to the mass extinction event,” said Schoene. “Our data show that maybe the second pulse could have played an important role in the extinction itself because it happened right before it.”

Keller is more definitive in her conclusions: “Deccan volcanism is the most likely cause of the dinosaur mass extinction,” she said. “The Chicxulub impact may have contributed to their demise, though the timing and environmental effects of this impact still remain to be determined.”

“In general, I think this paper is significant and interesting,” said Pincelli Hull, an assistant professor of geology and geophysics at Yale who was not involved in this research and who has argued against the role of the volcano in the mass extinction. “The paper is a huge advance in timing the [Deccan Traps] eruptions, but how that relates to the timing of outgassing is still a major question that needs to be resolved to figure out exactly what the relevant roles of volcanism and impact were.”

The researchers will continue to tease apart the effects of the one-two punch of the Deccan Traps eruptions and the planet-shaking impactor, said Eddy. “Regardless, it seems like the end-Cretaceous was a terrible time to be on Earth.”

PRINCETON UNIVERSITY

Header Image – A view of the cliffs cutting through the Deccan Traps from near Mahabaleshwar, illustrating the dramatic landscape and thickness of the basaltic pile, which reaches over 11,000 feet. Princeton geoscientists Blair Schoene and Gerta Keller led an international team of researchers who have assembled the first high-resolution timeline for the massive eruptions in India’s Deccan Traps, determining that the largest eruption pulse occurred less than 100,000 years before the mass extinction that killed the (non-avian) dinosaurs. Credit : Gerta Keller, Department of Geosciences, Princeton University

- Advertisement -

Stay Updated: Follow us on iOS, Android, Google News, Facebook, Instagram, Twitter, Threads, TikTok, LinkedIn, and our newsletter

spot_img
Mark Milligan
Mark Milligan
Mark Milligan is a multi-award-winning journalist and the Managing Editor at HeritageDaily. His background is in archaeology and computer science, having written over 8,000 articles across several online publications. Mark is a member of the Association of British Science Writers (ABSW), the World Federation of Science Journalists, and in 2023 was the recipient of the British Citizen Award for Education, the BCA Medal of Honour, and the UK Prime Minister's Points of Light Award.
spot_img
spot_img

Mobile Application

spot_img

Related Articles

Significant multi-period discoveries in Delbrück-Bentfeld

An archaeological excavation in Delbrück-Bentfeld, a town in the east of North Rhine-Westphalia, Germany, has unearthed nearly 400 features of archaeological interest that span several centuries.

Excavation confirms the origin of Sheffield Castle

Archaeologists excavating the former site of Sheffield Castle site have confirmed that an artificial mound within the castle interior is a motte dating back to the earliest phase of the castle’s construction.

WWII bunker unexpectedly discovered during forest clearance works

A WWII bunker has been discovered during forest clearance works for the S17 Piaski–Hrebenne expressway in eastern Poland.

Salvage project reveals 500 years of Veracruz history

An archaeological salvage project in Veracruz, Mexico, has uncovered more than five centuries of the city’s urban development and everyday life.

Aerial photographs indicate an enormous Avar-Era cemetery

An analysis of aerial photographs has led to the discovery of a previously unknown Avar-era cemetery on the outskirts of Tatabánya, Hungary.

Excavations reveal a vast Roman villa complex

Archaeologists from Inrap have revealed a vast Roman villa complex during excavations in Auxerre, France.

Unprecedented Roman discovery in Ireland

Archaeologists have made an unprecedented Roman discovery during excavations at Drumanagh in north Dublin.

Exquisite marble sarcophagus unearthed near Caesarea

Archaeologists from the Israel Antiquities Authority (IAA), working on behalf of the Caesarea Development Corporation, have unearthed an exquisitely sculptured marble sarcophagus near the coastal city of Caesarea, Israel.