The Mother of All Accidents

By Sean B. Carroll By Sean B. Carroll April 21, 2021

In 2001, Seth MacFarlane was the 27-year-old executive producer and creator of the not-yet-hit animated show Family Guy. Having broken into the entertainment big leagues at such a young age, MacFarlane was invited back in September to address his alma mater, the Rhode Island School of Design. After giving a talk, he went out for what turned out to be a late night of drinking with some professors. 

The next morning, September 11, MacFarlane raced to catch an 8:15 a.m. flight out of Boston back to Los Angeles. He was too late—the flight was actually at 7:45 a.m.; his travel agent had written down the wrong information. MacFarlane was rebooked on a later flight and went to doze in the passenger lounge. He was awakened by a commotion as passengers gasped at news coverage from New York showing the North Tower of the World Trade Center aflame. A short while later, the plane that struck the Tower was identified as American Airlines Flight 11 from Boston to Los Angeles—the flight MacFarlane had missed. 

Had the asteroid arrived 30 minutes sooner or 30 minutes later, the dinosaurs would still be here.

Actor Mark Wahlberg had also been booked on that same flight. A rising star known for his work in The Perfect Storm and Boogie Nights, Wahlberg and some friends changed their plans and hired a charter plane to a film festival in Toronto. They later flew on to Los Angeles.

Eleven years later, MacFarlane and Wahlberg teamed up to make the film Ted. So, just what are the odds that these two guys would both miss Flight 11, and later make a hit movie together? Were their escapes from mass murder just dumb luck, or was there a greater purpose at work? Were MacFarlane and Wahlberg spared so that our lives would be enriched by a pot-smoking, trash-talking teddy bear come to life? Or, so that movie industry coffers would be enriched by more than $500 million? 

MacFarlane himself doesn’t think so. “Alcohol is our friend, that’s the moral of that story,” he offered. “I am not a fatalist.” 

Dumb luck, happenstance, accident—call it what you will. MacFarlane’s late arrival to the airport was purely an accident, albeit an accident with enormous personal consequences. It is sobering to think what a thin line there can be between victim and survivor, between life and death. What a difference just 30 minutes can make.

TED TALK: Author Sean B. Carroll and Seth MacFarlane share a laugh at the Science & Entertainment Exchange of the United States National Academy of Sciences. During their talk, filmmaker MacFarlane recounted his fortune at missing his flight on one of the 9/11 planes.United States National Academy of Sciences

It’s a thin line in nature as well, not just for individual creatures (think of animal prey), or even species, but of whole worlds. Drive almost anywhere outside of a city, and the road is likely cut in places through a rock bed. Chances are most of us just ignore the pages of history staring us in the face. But those stacks of often colorful stone tablets tell stories, if you know how to read them.

Strada regionale 298 winds through a limestone gorge just outside Gubbio, a charming medieval town in the Umbria region of central Italy. In the mid-1970s, geologist Walter Alvarez saw an interesting pattern in a column of rock very close to the road. He noticed that in one section of the many layers of limestone, there was a switch in color, from white below to red above. When Alvarez looked closer, he saw that there was a peculiar layer of greyish clay separating the two colors of rock. Alvarez’s decryption of that one centimeter thin line would lead to one of the most stunning and revolutionary scientific discoveries of the 20th century and begin to tell the story of the most important day on Earth in the last 100 million years—a day that was very, very unlucky for most everything alive, but would eventually turn out to be extremely fortunate for us. And on that day a long, long time ago, 30 minutes would make all the difference.

One way that geologists characterize rocks is by the fossils they contain. The Gubbio rock formation was once part of an ancient seabed, so it contained the fossilized shells of tiny creatures called foraminifera, or “forams” for short.

When Alvarez looked at the forams from the rock cut outside Gubbio, he saw that the white layer of rocks contained a diverse array of large fossil forams. But the reddish layer of rock just above it lacked those species and contained only a few, much smaller species of forams. And the thin layer of clay in between the two colors of rock appeared to lack fossils altogether. Alvarez realized something dramatic had happened in the ocean that had driven many foram species extinct in a short period of time.

One thousand kilometers from Gubbio, at Caravaca on the southeast coast of Spain, Dutch geologist Jan Smit had noticed a similar pattern of changes in forams in rocks. Moreover, Smit understood that the line that lacked forams marked a well-known boundary in geology and Earth history, a dividing line between two worlds. Below the boundary lay rocks of the Cretaceous Period, named for characteristic chalky deposits, and making up the last third of the Age of Reptiles when dinosaurs ruled the land, pterosaurs patrolled the skies, and mosasaurs preyed on ammonites (close relatives of the nautilus) in the seas. Above the boundary lay rocks of the Paleogene, which contain none of these creatures, but mark the beginning of the Age of Mammals, in which furry animals emerged to become the largest animals on land and in the seas.

KNIFE’S EDGE: A line marks the Cretaceous-Paleogene boundary in southern Colorado. The white layer contains ejecta from the asteroid that hit Mexico 66 million years ago. Below, life before the asteroid; above, the mass extinction of about three-quarters of all species.Photo by Kirk Johnson; courtesy National Science Foundation

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.

It was the most important day on Earth—unlucky for most everything alive, extremely fortunate for us.

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?

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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.

The difference between the winners and losers was a matter of chance. The conditions triggered by the asteroid impact were beyond the experience of any creatures. Nothing in their evolutionary history prepared them specifically for years of hell. It was bad luck for the dinosaurs that the characteristics that made them dominant (e.g., large body size) made them vulnerable; good luck for a subset of mammals whose characteristics (e.g., small, burrowing) made survival possible, although not certain (the majority of mammals also perished).

The odds are not only against our existence without the asteroid, but the odds of an asteroid of sufficient size hitting the Earth are very low. The discovery of the K-Pg asteroid Chicxulub Crater spawned huge interest in other impacts. 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.

Sean B. Carroll is the author of A Series of Fortunate Events: Chance and the Making of the Planet, Life, and You. He is an award-winning scientist, writer, educator, and film producer. He is Vice President for Science Education at the Howard Hughes Medical Institute and the Balo-Simon Chair of Biology at the University of Maryland. His books include The Serengeti Rules, Brave Genius, and Remarkable Creatures, which was a finalist for the National Book Award. He lives in Chevy Chase, Maryland. Twitter @SeanBiolCarroll

Adapted from A Series of Fortunate Events: Chance and the Making of the Planet, Life, and You by Sean B. Carroll. Copyright © 2021 by Sean B. Carroll. Reprinted with permission from Princeton University Press.

Lead image: Festa / Shutterstock