Event 22

65 million years ago

Tyrannosaurs in meteor shower

The last day of the Cretaceous, 65 million years ago. A Tyrannosaurus rex is startled by the nearby cataclysmic impact of an extraterrestrial object (a huge asteroid or comet) that appears to have caused the extinction of the dinosaurs.

Credit: Illustration by John Sibbick, courtesy of John Sibbick Illustration. This illustration used with permission. All rights reserved.

Imagine the worst day of your life. Multiply that by the largest number you can think of. That’s the kind of day you would have had some 65 million years ago when a six-mile-wide asteroid struck the earth, travelling as fast as 5,000 miles per hour. Its impact created a catastrophic explosion – triggering massive earthquakes, creating gigantic tidal waves, igniting massive forest fires, and releasing huge quantities of acidic gases into the atmosphere to fall to the earth as acid rain. A massive dust cloud would have covered the earth, blocking sunlight and creating a so-called cold “nuclear winter” for several years, killing much of remaining vegetation, followed by a stifling “greenhouse” warming period. This was the second largest extinction event in the history of the earth, with 75 percent of all species going extinct, including all of the large land reptiles (dinosaurs), sea reptiles (plesiosaurs), and air reptiles (pterosaurs). Luckily, many smaller reptiles, birds, fish, and mammals survived this terrible event and continued on to inherit this brave new world.

Another event that may have contributed to the demise and extinction of the dinosaurs is the rise of widespread, violent volcanic eruptions on Earth in the time leading up to the dinosaur mass extinction. Between 70 and 65 million years ago, volcanic eruptions produced absolutely massive lava flows, such as the ones in the Deccan region of India (called the “Deccan Traps”), where lava flows spread over a region of a couple hundred thousand square miles and sometimes more than a mile deep. Much of this volcanic activity appears to have begun 65.5 million years ago and lasted for a million years.


Dinosaur extinction
An impact event that occurred around 65 million years ago is believed to have led to the extinction of the dinosaurs, and contributed to the rise of mammals.
Credit: Illustration by Zina Deretsky, NSF/ Wikipedia.


Within the geological layer produced at the time of this impact (the 65 million-year-old K-T, meaning ‘Cretaceous –Tertiary’, boundary), Nobel prize-winning physicist Luis Alvarez and his son, geologist Walter Alvarez, identified a widespread, one-inch layer of dark clay that contains very high levels of iridium, an element extremely rare on the earth’s surface but very common in meteorites and asteroids. In this rock zone there are also ‘shocked’ quartz grains only known to be created by massive explosions, many tiny glassy drops of solidified molten rock, and geological evidence of gigantic tidal waves (tsunamis). Finally, in 1992, scientists identified and reported a huge 125-mile-wide crater in the area around Chicxulub, at the edge of the Yucatan peninsula in Mexico, dating to the same age as the K-T extinction and also with very high iridium levels in its center. This appears to have been ‘ground-zero’ for this devastating asteroid impact.

It is also suggested that iridium contained within the earth could have been released during the extreme volcanic activity of this time period, thus contributing to the iridium layer that has been observed. Such cataclysmic events – the impact of such a massive asteroid and the extreme volcanic activity of 65 million years ago – would have clouded the atmosphere with dust, ash, and greenhouse gasses, obscuring the sun and raising world temperatures, and potentially cause widespread ecosystem collapse.



Had it not been for this random, catastrophic extraterrestrial event, it is likely that reptiles, including the dinosaurs, would have continued to be the dominant life form today. It is even possible that some of the larger-brained forms, such as the raptors, could have evolved into intelligent, tool-using sapient-like creatures. The extinction of the dinosaurs created vast new niches and opportunities for the mammals, including our own Order, the Primates. Although the majority of the extraterrestrial impacts on earth seem to have occurred early in its history (about 4.5 to 4.0 billion years ago), it is sobering to realize that massive impacts have also occurred in more recent earth history – and could happen again in the future.





The audio on this video is a little fuzzy, but the information is sound, and there is a little segment near the end on how scientists plan to avoid a similar asteroid strike in the future. This is from NASA.

Here is Smithsonian’s website on the explanation of why dinosaurs went extinct.

“Dinobuzz” is a question and answer website about dinosaurs developed by the University of California Museum of Paleontology (UCMP).

This is UC Museum of Paleontology’s dinosaur web site.

This is UCMP website that discusses the various theories as to why the dinosaurs became extinct.


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