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Scientists say asteroid-powered volcanoes killed dinosaurs



It's been almost 40 years since scientists discovered what destroyed dinosaurs: an asteroid hitting the Earthnear modern Mexico. That was it or that's what we thought.An article published today in Science supports an alternative hypothesis: catastrophic events following the impact could have contributed to the disappearance of dinosaurs and many other forms of life.

This builds on previous work – including some published last year – suggesting a link between the impact of the asteroid, the increase in volcanic eruptions and the impact of the earthquake. mass extinction event.

Brutal shock

In 1980, the American experimental physicist Luis Alvarez, his son geologist Walter and their colleagues published an influential article in the journal Science. They expose the evidence of a global catastrophe, buried in a layer scattered all over the planet, about 66 million years ago.

They found high levels of iridium – a rare element in the earth's crust, but common in meteorites. They found shocked quartz grains containing fractures indicative of the shock wave of impact, as well as traces of molten rock projection from impact shock.

With the subsequent discovery of the Chicxulub impact crater on the Yucatan Peninsula, Mexico, the case seemed closed. The reign of the dinosaurs ended with a meteorite impact, marking the end of the Cretaceous and the beginning of the paleogenic period, called the K-Pg limit.

Was there anything else?

Yet within the Earth Sciences community, discontent has continued to simmer. Two of the largest mass extinctions of the geologic register coincide with the largest basalt episodes exposed to continental flooding over the past 542 million years.

It's the end of the Permian 251 million years ago and, as the scientific paper of today points out, the extinction of the dinosaurs at the end of the Cretaceous 66 million years ago. The coincidence seems too great.

To understand the link between flood volcanism, meteorite impacts and extinctions, the moment is crucial.

In the new Science article, a team from the United States and India presents some of the most accurate dates for the huge eruptions in India, in a unit known as Deccan Traps – a huge province of basalt flooded in western India covering more than 500,000 km2 and in places is more than 2 km thick.

Map depicting the exposed areas of Deccan traps in modern India. Courtney's Sprain

They discovered that the best date for the impact of Chicxulub – 66.052 million years ago – was within 50 000 years of the peak eruption of Deccan Traps, which means that the The impact and rise of volcanism was essentially simultaneous.

A seismic connection

A link between an impact in the Caribbean and volcanism in the Indian Ocean may seem tenuous, but in global science, these associations are not uncommon.

The Caloris basin on the planet Mercury is a striking example. It is a 1,500 km wide structure from a previous meteorite.

The antipode (located on the other side of the planet) is a strange and fractured landscape called the disturbed terrain, formed by shock waves caused by the impact of Caloris.

This is a precedent – an impact can create geological changes at very long distances. But back on Earth 66 million years ago, Chicxulub and Deccan traps were not quite antipodal.

The Deccan traps were formed when this part of present-day India roughly covered the present island of Reunion, a small French island located near Madagascar. This island is still active on the volcanic level and is fed by the same rise of mantle that caused the Deccan volcanism. The Yucatan Peninsula, like most of the Americas, was significantly closer to Europe (see below).

Reconstruction of the Earth's plates 66 million years ago. The stars show the position of Deccan traps near India and the impact of Chicxulub in Mexico. Image created by C O'Neill using GPlates (Gplates.org), Author Provided

But that may not matter. It has long been argued, since Charles Darwin at least in 1840, that earthquakes could trigger eruptions.

The mechanisms are not well understood. Suggestions range from the formation of bubbles in magmas to the development of fractures in the crust allowing the magma to escape more quickly. It has been recognized, however, that despite their distance from earthquakes, some volcanoes are simply more sensitive to seismic activity than others, especially very active volcanoes. Few volcanic events were more active than Deccan traps.

Deccan Traps, lava flows in Western Ghats, India. Courtney's Sprain

Increased volcanic activity

Parallel to the rise of the Deccan volcano, the global system of mid-oceanic ridges of the Pacific and Indian Oceans seems to have increased activity.

Formed when two plates separate, the ocean ridges form the largest volcanic system on the planet. The overall gravity analysis revealed an unusually thick crust at the K-Pg boundary, formed due to excessive volcanic activity. This effect is only seen in the most extensive and therefore the most volcanic systems of the Pacific and Indian Oceans.

Together, these observations suggest a global impulse of volcanic contribution at the time of the mass extinction of the Cretaceous, pulled by the shock wave of the Chicxulub impact.

wreck

Exactly how this perfect storm of natural disasters – an asteroid collision and increased volcanic activity – has led to the massive extinction of so many lives on Earth is unclear at the moment.

Courtney Sprain, former author of UC Berkeley, is the first author of the journal Science. PhD student now at the University of Liverpool, UK, says:

Either the Deccan eruptions have not played a role – which seems unlikely to us – or a lot of climate-modifying gases have been released during the lowest eruption volume impulse.

Volcanism can warm the Earth due to the eruption of greenhouse gases like methane and carbon dioxide. In addition to impacts, it can also cool the atmosphere by adding aerosols of sulfur or dust, respectively.

The gases can also reach the atmosphere by cooking the magma below the surface, even without rashes. It is not clear how all of these factors combined to decimate terrestrial and marine ecosystems, but a clear calendar of events is essential to unraveling these interactions.

This article is republished from The Conversation by Craig O'Neill, Director of the Macquarie Planetary Research Center / Associate Professor of Geodynamics, Macquarie University, under Creative Commons license. Read the original article.

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