We don’t Know Exactly When the Dinosaurs Died, but Now We Know it was in the Springtime

We’ve long known a disaster took place about 66 million years ago, where in a geological instant, 75% of the plants and animals on Earth were wiped out, including all the land-roaming dinosaurs. But here’s a new detail about that event: Even though we can’t pinpoint exactly what year this disaster took place, we now know it happened during the springtime.

Most scientists agree the disaster was an asteroid impact, where an asteroid at least 10 kilometers wide struck the Chicxulub region in the present-day Yucatán Peninsula in Mexico. The impact released 2 million times more energy than the most powerful nuclear bomb ever detonated.

While previous studies looking at the timing of this event have focused on millennial timescales, a new study from Melanie During and colleagues from the University of Sweden focused on pinpointing seasonal information of fossilized fish found in a site in North Dakota, that perished as a result of the devastating impact.

The devastation created layer of ash sandwiched between layers of rock, known as the Cretaceous-Paleogene (K–Pg) boundary, formerly known as the Cretaceous–Tertiary (K-T) boundary, which is found across the world in the geologic record. It includes a layer of iridium, an element common in asteroids but rare on Earth. It was this ‘iridium anomaly’ that first revealed the extinction event as an asteroid strike to geologists more than three decades ago.

Artistic reconstruction by Joschua Knüppe of the Seiche wave surging into the Tanis river, bringing in fishes and everything in its path (dinosaurs, trees) while impact spherules rain down from the sky. Some dinosaurs are still trying to get away but we know they will not get far. Ants try to get back into their nest as the just blooming dianthus in the foreground are already being impacted by the impact spherules. Credit: Joschua Knüppe

Well-preserved fossil bones of filter-feeding sturgeons and paddlefishes found in the Tanis fossil site in North Dakota had impact debris lodged in their gills, but nowhere further down the digestive system, suggesting an almost-instantaneous death occurred when an impact-triggered seiche –continental water shaken by the impact — caused a sudden upriver surge.

The researchers found distinct growth patterns in the fossils that provided record of seasonal change, of when the fish had reproduced and had developing offspring. In the northern hemisphere, this would have been in the spring.

A paddlefish from Tanis. On the right, the rostrum (paddle) is missing and on the left everything behind the shoulder fin is missing. Credit: European Synchrotron Radiation Facility

“We postulate that the timing of the Chicxulub impact in boreal spring and austral autumn was a major influence on selective biotic survival across the Cretaceous–Palaeogene boundary,” the authors wrote in their paper, published in Nature.

The timing of the collision, at least for the Northern Hemisphere, would have come at a particularly sensitive stage in the biological life cycles of many plants and animals.

“I think spring puts a large group of the late Cretaceous biota (animal and plant life) in a very vulnerable spot because they were out and about looking for food, tending to offspring and trying to build up resources after the harsh winter,” Melanie During said at a news briefing.

By contrast, the researchers said that ecosystems in the Southern Hemisphere, where it was fall when the asteroid collided with Earth, appear to have bounced back nearly twice as fast as those in the Northern Hemisphere.

Three-dimensional rendering of the subopercular and gills in a with trapped impact spherules (yellow). Credit: During et al, Nature.

Even though these fossils were found 3,000 kilometers (1,864 miles) away from the impact crater, the details of the dig show the large fish – which are up to a meter (3 feet) long — died dramatically shortly after the asteroid strike. They were buried alive by sediment displaced as a massive body of water unleashed by the asteroid strike moved upstream.

Impact spherules — small bits of molten rock ejected from the crater went high into the atmosphere or even to space where they crystallized into a glass-like material — were found lodged in the fishes’ gills.

“These impact spherules got ejected into space, …and rained back down on Earth,” During said. “This deposit literally looks like a car crash frozen in place. It looks like the most violent thing I have ever seen, preserved in pristine condition.”

This new study coincides with previous studies from as early as 1991 which showed fossils in the same condition, which suggested is happened in June, along with another study from December of 2021, which also concluded the extinction event happened in spring.

Lead image caption: Melanie During excavating a paddlefish in the Tanis deposit. Credit: Jackson Leibach, via Nature.

Additional reading: Nature press info, and paper

Nancy Atkinson

Nancy has been with Universe Today since 2004, and has published over 6,000 articles on space exploration, astronomy, science and technology. She is the author of two books: "Eight Years to the Moon: the History of the Apollo Missions," (2019) which shares the stories of 60 engineers and scientists who worked behind the scenes to make landing on the Moon possible; and "Incredible Stories from Space: A Behind-the-Scenes Look at the Missions Changing Our View of the Cosmos" (2016) tells the stories of those who work on NASA's robotic missions to explore the Solar System and beyond. Follow Nancy on Twitter at https://twitter.com/Nancy_A and and Instagram at and https://www.instagram.com/nancyatkinson_ut/

Recent Posts

Here’s How Interstellar Objects and Rogue Planets Can be Trapped in the Solar System

When Oumuamua traversed our Solar System in 2017 it was the first confirmed Interstellar Object…

4 hours ago

MeerKAT Confirms the Gravitational Wave Background of the Universe in Record Time

Astronomers are collecting evidence for the gravitational wave background of the Universe, caused by merging…

5 hours ago

Could We Use An Asteroid to Shield Astronauts On Their Way to Mars?

Radiation is a primary concern for long-duration human spaceflight, such as the planned trips to…

7 hours ago

Maybe Venus Was Never Habitable

The planetary science community argues back and forth about when Venus was last habitable. Did…

8 hours ago

Astronauts on Long Missions Will Need Personal AI Assistants

How can artificial intelligence (AI) help astronauts on long-term space missions? This is what a…

21 hours ago

Could Primordial Black Holes Be Hiding in Plain Sight?

Are Primordial Black Holes real? They could've formed in the unusual physics that dominated the…

1 day ago