The Dinosaurs Got a Warning Shot

Over the weekend I came across an excitedly-headlined BBC report suggesting that not one but two impacts in quick succession doomed the dinosaurs 65 million years ago.

A cataclysmic impact 65 million years ago disrupted the world's climate and wiped out most flora and fauna on Earth, including the dinosaurs. This painting depicts the scene a few seconds after the body struck just north of what is now Mexico's Yucatán peninsula.
Don Davis / Sky Publishing / Cambridge University Press
One was the giant, now-famous pounding called Chicxulub that gouged out a crater 110 miles (180 km) wide in what's now the Yucatán Peninsula. The other was a smaller crater named Boltysh, only 16 miles (24 km) across, in central Ukraine.

I thought, "Hmm . . . this sounds familiar" — and I was right.

Loyal followers of S&T.com will remember reading about Boltysh in 2002. That's when Simon P. Kelley (Open University, United Kingdom) and Eugene Gurov (National Academy of Ukraine) used isotopic dating to show that the Boltysh impact occurred 65.2 million years ago, give or take several hundred thousand. Chicxulub is a little older, 65.5 million years, but the dating uncertainties overlapped enough that the two hits might have been nearly simultaneous.

Boltysh region
The Boltysh impact event occurred some 65 million years ago when a meteor impact crated a 24-km-wide crater in the Ukraine. Click on the image for a wider view.
Geologists realize that Boltysh is too small to have played a role in the near-total destruction of life on Earth that did in the dinosaurs, a biological hiatus known as the Cretaceous-Paleogene extinction. (You thought it was "Cretaceous-Tertiary," didn't you? The naming convention got changed in 2004.) Statistically, an asteroid or comet creates a Boltysh-size hole on Earth roughly every million years. Sure, it would have been ugly for anything foraging along the Dnieper River that day, but life elsewhere would not have been affected in a serious way.

So why the renewed fuss? You can dismiss the BBC's headline — Boltysh wasn't found to be riddled with plant-munching alien spores or anything else that would change its status as a secondary blip in the dinosaurs' demise.

Instead, in the August issue of Geology, David Jolley (King's College, Scotland) and four colleagues describe what they found after drilling deep into the sediments that now fill the crater's floor. It turns out that ferns and flowering plants had just begun to flourish in the region's recovering ecosystem — only 2,000 to 5,000 years after the impact — when they were wiped out by the aftermath of Chicxulub's much-bigger blast.

Boltysh crater samples
David Jolley (left) and Jon Watson unload some of the core samples taken from a 2008 drill hole in the Boltysh crater.
CESAR / Open University
Cosmically speaking, the chance of Earth getting nailed twice in such quick succession by impacts of this size is only about 1 in 1,000, so this was no coincidence. Nor were Boltysh and Chicxulub simultaneous — it wasn't a binary asteroid.

Instead, Jolley and his team (which includes Gurov and Kelley) suggest that something must have stirred up the asteroid belt enough to redirect multiple large bodies Earth's way. Perhaps two large asteroids collided about that time, spraying a shower of fragments throughout the inner solar system, or maybe a clutch of asteroids were yanked into Earth-crossing orbits due to a gravitational resonance with Jupiter.

Whatever the cause, Chicxulub likely resulted from an asteroid of some kind, likely a carbonaceous chondrite, based on the tiny piece of one that UCLA researcher Frank Kyte found a decade ago in a deep-sea drill-core from the central Pacific Ocean. So, just like T. rex and its buddies, the idea that a rogue comet caused the Cretaceous-Paleogene extinction is probably dead too.

7 thoughts on “The Dinosaurs Got a Warning Shot

  1. Nola redd

    Now I have to wonder if there is any evidence of bombardment dating around the same time period on other surfaces we’ve observed.

  2. Stan Kerns

    I am have no problem with Chicxulub driving the final nail in the dinosaur’s coffin–but had you a time machine and were selling “see the dinosaurs” trips–and went to just pre Chicxulub time most of your travelers might ask for their money back–dinosaurs had been on a steep decline for millions of years–and not a whole lot were left. Lots of stuff did go extinct though.

  3. Alphacygni

    So…. was the Tunguska event in 1908 our “warning shot?
    No one knows the time or date of the next one, so don’t lose
    any sleep over it.

  4. Vladimir

    I take it that, since it, actually, occured “nearby” last time as I live in Kiev – not far from that place, an asteroid should smash next time into the Earth elsewhere…according to statistics))) – Just a tiny hope..))

  5. Jeff

    Stan Kerns comment above is right on the money. Many species of dinosaurs were already extinct. At least in North America there were a number of ongoing geologic changes that certainly had a impact (no pun intended) on habitats and likely contributed to stresses on diffferent animal species.
    Whatever struck the final blow did so in a big way. Dinosaurs, pterosaurs, marine reptiles, invertebrates such at the beautiful ammonites- were all gone in a very short span of time. It wasn’t the first time (there was a mass extinction at the end of the Permian), nor the last (another large-scale extinction followed during the Eocene) that such events have happened. Each time the plants and animals that have disappeared have been replced with something else. It’s a wonderful commentary about the adaptability of life on the only known inhabited world!

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