For over 180 million years of the Earth’s existence, dinosaurs reigned supreme, dominating food chains and contributing to the planet’s evolutionary progress.
Then suddenly, 66-64 million years ago, they went extinct. This significant epoch in natural history is often termed the first “mass extinction”.
Until 1980, few satisfactory answers were offered to solve the mystery behind the extinction of dinosaurs. Scientists at the University of California at Berkeley proposed a mechanism called “K-T extinction” [i.e. the extinction of dinosaurs at the cusp of the Cretaceous period (K) and the Tertiary period (T)]. For context, ‘K’ is dated 145-66 mya, followed by the onset of ‘T’. And the dinosaurs as we know and identify them today, were all but gone during this period, in what some scientists also called as the “great dying” -- an episode in evolutionary history where more than 50% of all known species living at that time went extinct in a short period (less than 2 million years or so).
Several fossil records studied, deciphered and catalogued using carbon-dating and more sophisticated methods, have allowed scientists to arrive at a common thread of hypotheses, involving the timeline of extinction, cause, and ramifications of the epochal event. As is known, extinction, especially from natural factors and not so much human intervention, is complex, taking a prolonged period. It is not simply the death of all representatives of a group, but rather the cessation of the origination of new species that renders the group extinct. Simultaneously, all means of procreation or survival cease to function, rendering the ultimate end of the group inevitable. Scientists found that new dinosaur species ceased to originate around the K-T boundary, with the question remaining to be answered -- what killed them?
Asteroid or Volcano?
Answering that very question, in 1980, Nobel laureate physicist Luis Walter Alvarez and his geologist son Walter published a paper that a historic layer of iridium-rich clay was created by a large asteroid colliding with Earth. This was linked to a 6-mile-wide asteroid that hit the coast of the Yucatán Peninsula in Mexico 66 mya, obliterating all life, including dinosaurs, within a few thousand-mile radius. This asteroid collision with Earth filled the sky with dust material, plunging the planet into a devastatingly long winter, which unleashed a chain of catastrophic events that led to the doom of most dinosaurs, while some smaller species were already evolving as a natural balancing act (such as giving rise to birds). Along with dinosaurs, other animals also died out, including pterosaurs, marine reptiles, and ammonites.
A growing body of geological evidence today, however, suggests that the dinosaurs were already enduring climatic chaos before the asteroid, owing to relentless volcanism, especially in India’s Deccan Traps.
According to a new study published in Science Advances, co-authored by Don Baker, a professor at McGill University’s Department of Earth and Planetary Sciences, the celestial body crashing into Earth is only part of the story. The world during that prehistoric period was a very different, inhospitable place. Volcanism and extreme climatic shifts were very common, and the flora and fauna had adapted accordingly.
The McGill study states that “climate change triggered by massive volcanic eruptions may have ultimately set the stage for dinosaur extinction, challenging the traditional narrative that an asteroid alone delivered the final blow to the ancient giants”.
The research team studied volcanic eruptions of the Deccan Traps -- a vast and rugged plateau spread across Maharashtra, Goa, Gujarat, Madhya Pradesh and Rajasthan, formed by molten lava. Erupting a staggering 1 million cubic km of rock, it may have played a key role in cooling the global climate around 65 mya. The team studied rocks in the Traps, while analysing the samples in England and Sweden.
Around 300,000 years before impact, and for another 500,000 years after it, these eruptions emitted vast clouds of carbon dioxide and sulphur dioxide. The CO2 heated the planet -- just as man-made emissions are doing today -- while the SO2 cooled it by reflecting the Sun’s energy back into space. This climatic see-saw created a whiplash that heralded a mass extinction. Hence, the team deduced that the asteroid wasn’t the sole death knell for the dinosaurs, but perhaps the final nail in their coffin.
The Earth is ageing, ever-evolving, and changing for the last 4.5 billion years. It has gone through infinite phases of climate change, which by definition is a naturally occurring process, brought about by the Sun’s intensity, volcanism, and changes in natural greenhouse gas concentrations. Human intervention in modern times, however, has expedited it to the point of uncertainty.
Meanwhile, in their lab, the McGill scientists estimated the amount of sulphur and fluorine injected into the atmosphere by massive volcanic eruptions in the 200,000 years before dinosaur extinction. It was found that the sulphur release could have triggered a global drop in temperature around the world -- a phenomenon termed ‘volcanic winter’.
“Our research demonstrates that climatic conditions were almost certainly unstable, with repeated volcanic winters that could have lasted decades, prior to the extinction of the dinosaurs. This instability would have made life difficult for all plants and animals and set the stage for the dinosaur extinction event. Thus, our work helps explain this significant extinction event that led to the rise of mammals and the evolution of our species,” says Prof Baker.
The team propounded a new technique to decode the volcanic history, and estimating the sulphur and fluorine releases. “Imagine making pasta at home. You boil the water, add salt, and then the pasta. Some of the salt from the water goes into the pasta, but not much of it,” explains Prof Baker.
Similarly, some elements become trapped in minerals as they cool following an eruption. Just as you could calculate salt concentrations in the water that cooked the pasta from analysing salt in the pasta itself, the new technique allowed scientists to measure sulphur and fluorine in rock samples. With this information, the scientists could calculate the amount of these gases released during the eruptions. Hence, the dinosaurs were already finding it hard to adapt and survive in those rapidly changing times. The fresh findings not only pave the way to decode Earth’s ancient secrets, but also build a more informed approach to understand today’s climate change challenges.