Evolution: driven by extinctions: Chixculub luck or aimed (Evolution)

by David Turell , Thursday, April 22, 2021, 15:06 (1309 days ago) @ David Turell

Gerald Schroeder first raised the issue, luck or God's aim, now discussed again by SEAN B. CARROLL:

https://nautil.us/issue/99/universality/the-mother-of-all-accidents?mc_cid=f22b7ca090&a...

"The Cretaceous-Paleogene boundary (known as the K-Pg for short; formerly known as the K-T) marks not only the extinction of dinosaurs, pterosaurs, mosasaurs, and ammonites, but the mass extinction of about three-quarters of all species living around the globe 66 million years ago. Alvarez, Smit, and their colleagues wondered: What on earth could have caused the disappearance of widespread, tiny organisms like forams, as well as much larger creatures?

"The short answer, as you most likely have heard, is that it wasn’t something on Earth, but something from space.

"Chemical analyses of the clay marking the boundary of the two periods, carried out by Alvarez, Smit, and their collaborators, revealed that it contained extraordinary levels of the element iridium, a material rare on Earth but more abundant in certain kinds of asteroids.

"From the amount of iridium found in the boundary layer, Walter Alvarez’s father Luis Alvarez, a Manhattan Project veteran and Nobel Prize-winning physicist, calculated the size of an asteroid that would be necessary to coat the globe in iridium. He figured that the asteroid would have been about 6 miles (or 10 kilometers) wide.

***

"Alvarez, Smit, and their collaborators forwarded the asteroid impact scenario for the mass extinction in 1980. It was a revolutionary, many would say radical, and some would say too radical, idea.

"Finally, in 1991, a 100-mile wide crater was identified that lies partly underneath the village of Chicxulub on Mexico’s Yucatan Peninsula, and was shown to be of the very same age as the K-Pg boundary. The smoking hole had been found.

"Since the discovery of the Chicxulub crater, many kinds of scientists—geologists, paleontologists, ecologists, climatologists—have worked to unravel how the K-Pg impact triggered a mass extinction and to understand which species perished, which survived, and why?

"The important question for us though is: Would we be here without the asteroid collision?

"To answer that question, we need to weigh a few facts. First, mammals evolved well before the K-Pg extinction. They had coexisted alongside the great dinosaurs for 100 million years, and scores of species are known from various parts of the world from the late Cretaceous period. So, the presence of dinosaurs did not preclude furry mammals from arising. But second, mammals were relatively small-bodied, suggesting that they filled niches that the dominant dinosaurs did not. And third, within just a few hundred thousand years after dinosaurs disappeared, mammals became much larger than at any time in the previous 100 million years. This very rapid increase in average and maximum body size post-extinction suggests that the dinosaurs were a major force in limiting their size. It stands to reason, then, that without the asteroid impact the dinosaurs that had reigned for more than 100 million years would likely still be here, and therefore the primates would not be, and so neither would we.

***

"It turns out that no other asteroid strikes of the magnitude of the Chicxulub impact have occurred in the last 500 million years on Earth or the moon (which receives a similar population of incoming bodies). To trigger a mass extinction, size matters. With an incidence of just one, all we can say is that Chicxulub is perhaps a 1 in 500 million years (or longer) event.

"Moreover, it turns out that, even with a large asteroid, the location of the impact also matters. The rocks around the Yucatan target site are rich in hydrocarbons and sulfur, which resulted in the production of enormous quantities of soot and sunlight-deflecting aerosols. Geologists figure that as little as 1 to 13 percent of the Earth’s surface contains rocks that could have yielded a comparable stew of destructive materials.

"This small target means that with the Earth rotating at about 1,000 miles per hour, had the asteroid arrived just 30 minutes sooner, it would have landed in the Atlantic Ocean; 30 minutes later, in the Pacific Ocean. Just 30 minutes either way and the dinosaurs would probably be here, and there would be no Ted and, God forbid, no Ted 2."

Comment: We are here. Luck or God's aim? It depends upon whether you are a theist or a materialist/naturalist.