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How did all dinosaurs except birds go extinct?

The extinction of non-avian dinosaurs except birds at the end of the Cretaceous has intrigued paleontologists for more than a century.
Volcanic eruptions are one of the most powerful forces of nature. The Deccan Traps are a series of geological formations located in western India that record one of the largest volcanic eruptions in Earth’s history. These eruptions started close to the end of the Cretaceous Period and produced massive lava flows that spanned more 600,000 square miles.
We now know that the Deccan volcanic eruption occurred throughout 700,000 years in multiple events or pulses, and that one of these pulses was far larger than the others (responsible for 80 percent of the erupted volcanic rocks) and its age places it awfully close to the K-Pg boundary.
A massive volcanic eruption like this one would have released enormous amounts of volcanic gases into the atmosphere, which could have altered the global climate, making the Deccan Traps a serious candidate for contributing to the end-Cretaceous environmental changes and mass extinctions.
In the late 1970s, at about the same time that the Deccan Traps were proposed as a potential cause of the end-Cretaceous mass extinctions, Walter Alvarez, a geologist from the University of California, Berkeley, was studying sediments of the K-Pg time period in the Italian Apennine Mountains (Fig. 4). Alvarez noticed a distinct 1-inch-thick black clay layer that marked the boundary and separated very distinct marine organisms below and above it. He wondered how much time that inch of black clay represented and asked his father, the Nobel Prize–winner Luis Alvarez, for ideas about how to measure it.
The Alvarezes had in front of their eyes an unequivocal indication that a massive asteroid must have collided with Earth right at the Cretaceous-Paleogene boundary. This finding was published in 1980, introducing what is known as the Alvarez hypothesis. The authors suggested the asteroid must have been about 6 miles wide, with the resulting impact crater approximately 100 miles wide. The impact of this giant bolide, traveling at 20 times the speed of a bullet, would have created a blast equivalent to 100 million nuclear bombs. The impact would have ejected tons of dust and debris into the atmosphere, with some of it even reaching outer space and eventually falling back to Earth. Up to 99 percent of sunlight would have been blocked for days or months, stopping photosynthesis and causing the collapse of ecosystems on a global scale.
Years before, in the late 1970s, geologists working for a Mexican oil company had discovered a ringlike structure near the Yucatan Peninsula while prospecting for possible drilling locations. This ringlike structure was partly submerged in the Caribbean and turned out to be the remnant of a giant crater formed about 66 million years ago. Moreover, it was about 110 miles wide, matching Alvarez’s prediction for the asteroid impact! However, the discovery was not published at the time, partly because of the secrecy of the oil industry and partly because it predated the publication of the Alvarez hypothesis, which prompted the search for a large crater.
In 1991, American geologist Alan Hildebrand obtained permission to publish the crater and other important data. This announced to the world that the crater of the dinosaur-killer asteroid had been found. The Chicxulub Crater, named after a nearby Mexican town, became instantly famous as the missing piece of evidence proving the Alvarez hypothesis.
The timing and the magnitude of both the Deccan Traps and asteroid events makes it impossible to ignore either of them as potential causes of the end-Cretaceous crisis. In 2014, Mark Richards, a geologist from the University of Washington, suggested that the seismic waves of impact from the asteroid could have triggered the onset of the major Deccan Trap pulse, reactivating the already existent volcanic system. The devastating effects of both the asteroid impact and the mega volcanic eruption could have been acting at the same time!
This idea is known as the one-two punch hypothesis, and its merit is still being debated. It is now clearer than ever that improvements in technology and the accuracy of radiometric dating will be key for telling apart the different events that resulted in the end-Cretaceous mass extinction event.

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