Today’s post is part of a special series here on Planet Pailly called Sciency Words. Each week, we take a closer look at an interesting science or science-related term to help us all expand our scientific vocabularies together. Today’s term is:
THE K-T EVENT
You already know this story. It was 65 million years ago. There were dinosaurs, there was an asteroid…
It’s easily the most famous asteroid impact in Earth’s history, and it’s called the K-T Event, or sometimes the K-Pg Event.
In geology shorthand, the letters stand for:
- K: the Cretaceous period, which is spelled with a K in German. This was the last period of geological history in which dinosaurs roamed the Earth.
- T: the Tertiary period, which immediately followed the Cretaceous. According to the International Commission on Stratigraphy (ICS), we’re not supposed to use this name anymore, but people still do. It’s sort of like how some people keep calling Pluto a planet, no matter what the International Astronomy Union (IAU) says.
- Pg: the Paleogene period, which is the period immediately following the Cretaceous according to the ICS’s new list of geological periods. Please note, the Tertiary and Paleogene are not really interchangeable terms. They have the same starting point, but different end points.
Geologists and paleontologists puzzled for decades over a layer of clay separating Cretaceous and Tertiary (or Paleogene) rock. They called it the K-T boundary. There were several competing hypotheses about what might have caused this boundary and how it related to the mass extinction event that killed off the dinosaurs.
Then in 1980, a paper came out entitled “Extraterrestrial Cause for the Cretaceous-Tertiary Extinction.” This paper reported the discovery that the K-T boundary contained abnormally high levels of the element iridium.
Platinum group metals like iridium are extremely rare on Earth (except in the planet’s core) but common in asteroids. So whenever you find lots of iridium in Earth’s crust, you can justifiably assume an asteroid put it there.
The most likely scenario is that a large asteroid, about 10 km in diameter, smashed into Earth, flinging dust and debris high into Earth’s atmosphere. Enough to block out the sun worldwide for several years. This global dust cloud would have included plenty of material from the asteroid itself, which would have been partially vaporized by the heat of the impact.
A major problem with the original 1980 paper was that, at the time, no known impact crater of the appropriate age was sufficiently large. But of course, that was back in 1980. The crater has since been found in the Yucatan Peninsula, and now just about everybody knows the story of the K-T Event (even if they don’t know it’s called that).
P.S.: The K-T Event is not to be confused with the Katie Event. You know, that time your BFF Katie had waaaaay too much to drink and threw a temper tantrum of apocalyptic proportions.
Addendum: While there does seem to be general, widespread consensus that the K-T asteroid impact either caused the extinction of the dinosaurs or contributed significantly to their demise, there is not universal agreement. As Planetary Defense Commander notes in the comments, there are other possibilities worth considering.
Planet Pailly 
I took a graduate course in mass extinctions, and I’m not on board with the asteroid theory. I know, it’s the party line right now, and you’re not supposed to ask questions in science… My opinion is based on a number of other asteroids of similar size that struck without causing mass extinctions. To me, flood-basalt volcanism events have a better correlation with mass extinctions. There are a half-dozen other causes with proponents, sounds like a new Planet Pailly series!
I’m always amused when the paleo people express certainty about their conclusions, given that their data always says +- x million years.
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You are always supposed to ask questions in science, and genuine scientific debates almost never say that something is proven. They speak instead in terms of high degrees of certainty or simplest explanations.
For the purposes of my blog, I try to stick to the scientific consensus where there appears to be one. I think you’re right that volcanism caused many if not most mass extinctions, but the broad scientific consensus seems to be that K-T mass extinction was a special case.
There’s strong evidence for a massive asteroid impact, and there’s strong evidence of a mass extinction occurring at roughly the same time. This could be a matter of pure coincidence (maybe the dinosaurs were already dying out when the asteroid happened to come along), but the consensus seems to be that a cause and effect relationship is more probable.
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You beat me to it, James. You’re always supposed to ask questions in science. Its why science has stood the test of time so well.
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I haven’t looked at it recently, but I believe there was a flood basalt event within the same time period. I’m not saying I know that’s what caused the extinction, but I am saying they don’t KNOW it was an asteroid.
I once saw some data that indicated a number of similar-magnitude asteroid strikes that didn’t cause extinctions, while every high-magnitude flood basalt event coincided with a wave of extinctions.
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Chemistken, I hope that’s still true in Chemistry, but it’s no longer true in the biological sciences, at least in the two US universities and one foreign university where I did my work.
Sometimes it’s just the petty biologist who sets out to destroy anyone who asks an innocent question about his pet theory.
Other times it’s politically-motivated. Example: I met a marine biologist with a decades-long record who worked at a prestigious institution. He had run a multi-year sampling program far more extensive than anything I’d seen in a published paper, but couldn’t get anyone to publish his work, because it showed that the regional decline of certain fish species was due to overfishing, not climate change.
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Okay, I’ve added an addendum to this post. After doing further research, I’ve found that there’s enough disagreement with the consensus view that it’s worth mentioning. And I’ll try to be more mindful of dissenting points of view in the future.
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I’m actually surprised you were able to locate any dissent after the high priests made their pronouncements — that’s encouraging. I don’t know whether the asteroid theory is right or wrong, but I do know they can’t be certain it’s right.
I’m still hoping I can talk you into doing a series of articles on all the different causes that have been put forward for various mass extinctions. It’s an interesting topic.
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I think that could be a very interesting line of research. Especially combined with other planet-scale disasters that are believed to have happened on Venus and Mars. I’ll keep it in mind for the future.
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