Science & Technology

You may have heard an asteroid ended the dinosaur era – but how?

You may have people blame a massive asteroid for killing off all the dinosaurs millions of years ago – but how did one rock, however big, cause a worldwide extinction event? A new study reveals that what really killed the dinosaurs might have been a worldwide “apocalyptic dust plume” that blocked out the sun for years after the asteroid’s impact.

The Ultimate Bad Day

An article from the National History Museum opens with “Sixty-six million years ago, dinosaurs had the ultimate bad day.” In 1980, Nobel Prize-winning physicist Luis Walter Alvarez published their theory of what caused the end of the dinosaurs: a massive asteroid hit Earth, causing a mass extinction event. While their theory was controversial in the early ‘80s, it’s now the most widely believed theory and considered by most of the scientific community to be the most likely to be correct.

If that sounds a lot like guessing, that’s because it is! Writing things down so that people in the future can read our history is a relatively new thing. The earliest known writing was invented in an area of the Persian Gulf called Sumer in about 3400 BC – but the world has been around a lot longer than 5,400 years! To determine what happened before the written record – or, for that matter, the existence of humanity – we have to analyze the evidence and make our best guess.

Asteroids are large, rocky bodies that orbit the sun (much like the planets of our solar system, Earth included). They range in size from several to hundreds of feet in diameter, and sometimes they’re drawn to other, larger bodies. When an asteroid hits Earth, any pieces that survive are called meteorites.

The Asteroid that is believed to have caused the extinction of about 75% of Earth’s animals, including the dinosaurs, was, as best as we can tell, probably between six and nine miles wide. But when it landed in modern-day Mexico, it left a crater between 124 miles across in the Yucatan Peninsula.

A 2022 study by the Geological Society of America estimates the impact hit 50,000 times harder than the magnitude 9.1 Sumatra earthquake in 2004, which itself caused a tsunami and was estimated to have released 23,000 times the energy as the atomic bomb dropped on Hiroshima in World War II. It would have caused giant earthquakes and mega-tsunamis, as well as wildfires.

Dinosaurs Just Couldn’t Compete

The new 2023 study, based on research of the sediment layers of the Tanis paleontology site in North Dakota, suggests a huge cloud of dust released into the atmosphere by the asteroid is what actually killed off most of the planet’s life. The scientists who conducted this research believe this dust stayed in the air for about 15 years, cooling the surface temperatures by 24 degrees and stopping photosynthesis – the process by which plants process sunlight and grow – for two years.

“Dust could shut down photosynthesis for such a long time that it could pose severe challenges,” explained planetary scientist Cem Berk Senal, who works at the Royal Observatory in Belgium and led the study. “It could result in a chain reaction of extinction to all species in the food chain.”

Clearly though, this didn’t wipe out all life on Earth. Why the dinos, then? It probably comes down largely to food availability. Today, the largest land animal alive is the elephant, which often grow to just shy of ten feet tall and weigh as much as 14,000 pounds. They can spend up to three-quarters of their day just eating, consuming about 330 pounds of vegetation a day.

(Photo by: Ken Welsh/Education Images/Universal Images Group via Getty Images)

Out of about 584 different dinosaurs, the average mass came out to about 7,700 pounds each. That’s a pretty big animal, somewhere between the modern-day rhinoceros and elephant. The sauropods, however, were a group of four-legged plant-eating dinosaurs with long necks and tails. They lived at the end of the Cretaceous Period, which is the era believed to have been ended by the asteroid, and they accounted for the largest animals in history that we know of. The largest of this group, the Argentinosaurus, may have been up to 130 feet long and weighed as much as 240,000 pounds. If this dinosaur ate the same amount relative to its own body weight as modern elephants, that means each individual would need to consume over 5,000 pounds a day!

By contrast, mammals at the time – and many other creatures, for that matter – were tiny and didn’t require as much food. As the plants died off, so too would the larger dinosaurs that needed thousands of pounds of vegetation per day. Smaller plants, which would be missed by such giants, may have sustained smaller creatures.

As for the meat eaters, The T-Rex, easily the most famous carnivorous dinosaur, may have been about 40 feet long, 12 feet tall, and weighed as much as 15,500 pounds. It’s also believed they had a top speed of about 15 miles per hour. Once the giant and fairly slow-moving plant eaters died out, the large meat eaters lost their food source as well. Smaller creatures easily outran the largest carnivores – even a human can run faster, in short bursts, than any speed the T-Rex is believed to have ever achieved. And even if these ancient predators could have caught – or would have even noticed – the smaller animals at the time, they would almost certainly spend more energy chasing and eating the tiny prey than they would get from the meal.  In short, they were just too big to survive such a deadly environment.