When did we find out that a meteor killed the dinos?

I remember as a young kid in the early 1980s learning about dinosaurs and hearing that their extinction was a total mystery. We didn’t know why it happened.

Now, we seem pretty sure that a large meteor landed in the western hemisphere and caused the extinction.

When did we become “pretty sure” that this is what happened?

A geological paper detailing the structure of the crater was published in the early 1990s which kinda sparked the whole thing off. It was fairly big news and was considered somewhat controversial throughout the early to mid 1990s. By the end of the 1990s the theory had gained significant acceptance, though some people still contest it today.

Seriously accepted following the work of Luis and Walter Alvarez:


Published in 1980.


The crater was discovered later. The Alvarez discovery was of the Iridium rich K-T boundary which they claimed was evidence of a large meteor strike.

Here’s the relevant wikipedia: http://en.wikipedia.org/wiki/Kt_event#Causes_of_extinctions

The discovery of the Chicxculub crater in 1990 and its subsequent dating was when things got more definitive.

But, get with the program! The tidy little narrative of “asteroid hits Earth, dinosaurs all die” isn’t as clear cut as it once seemed. For one, a lot of paleontologists have pointed out that dinosaurs as a group were in decine well before the K-T event (K-Pg in the new time scale), so at best you could only say that the asteroid sped things along.

Also there is the issue with the Deccan Trap flood basalts in India which also date to around the same time, but whose relationship to the K-T event, the mass extinctions and the Yucatan impact are not clear. A lot of people think that the long term climatic consequences of the flood basalts are a more likely cause of the mass extinction than the impact. But, again, the relationship between the Indian flood basalts and the Chixculub crater, if any, is not quite clear. One theory for a while was that the flood basalts had been caused by the impact’s effects punching through the mantle to the other side of the globe, but this has been largely discredited. Another idea is that there was a Shoemaker-Levy esque multi-part impact which might have included an even larger impact in India, but this idea has some dating and other geological issues as well.

So say tuned-- maybe in 10 or 15 years you’ll be asking when did we definitively do away with that nonsense about the asteroid killing the dinosaurs.

I had a letter published in New Scientist in 2002 pointing out this possibility; the Traps are almost opposite the Mexican crater site and on a comparable latitude:

I’ve been unable to find the response online, but IIRC it more or less said that while it was possible there was no real way to tell, as the dating of the two events couldn’t definitely say how close in time they were.

It’s an interesting notion, and I think it’s especially appealing because there really isn’t a very good explaination for large igneous provinces like the Deccan Traps(IMHO, anyways-- it’s a lot of fudging with mantle plumes). However the date on the earliest eruptions are pretty solidly at 68 million years with the bulk of the eruptions at 66, so establishing direct causation with an impact at 65 million is troublesome.

I think between the fairly close dates and the latitude thing, it seems kind of hard to definitively rule everything a coincidence. But on the other hand, part of what has lead to this whole discussion is that by looking at other mass-extinction events it seems that a single catastrophy by itself cannot cause truly awful mass extinctions like the end Permian and end Cretaceous ones. In the light of the fact that impacts seem to be more common than we once thought, it may just be that a coincidence of catastrophic events is what makes the difference between the two era-defining mass extinctions and the other more common smaller ones. So it may have been that the world-wide ecosystem that was already stressed by the climate change from the Deccan Traps and that the Chixculub event is what changed the mass-extintion already in progress into the truly definitive catastrophy it was.

Walter Alverez wrote a book about the whole episode: When he first came up with the theory, what other scientists thought about it, and the whole struggle to get his idea accepted. It’s calledT. Rex and the Crater of Doom.

It’s a very interesting book and an excellent introduction to what the scientific process looks like up close.

I saw Luis Alvarez talk about this at Princeton in 1981. At the time they were leaning to a crater around Iceland being the point of impact, but were far from sure. Yucatan wasn’t in the running yet.

And I second the recommendation of Walter Alvarez’s book.

This is as much a secondary question as much as commentary but it is my understanding that the dinosaurs never truly went extinct at all. Birds are dinosaurs are evolved directly from some of them. Some of the classical dinosaurs, maybe even T-Rex were feathered. I am sure this is a complex topic and no one knows the whole answer yet but I get the impression that popular knowledge lags behind scientific knowledge significantly in this area.

The positions of the two (Chicxulub and the Deccan Traps) right now is meaningless. It’s where they were 65Myears ago that’s significant. And there’s been a lot of tectonic movement in those 65Myears.

India has been moving mostly north, I believe, and was south of the equator then. That would make the latitude be closer to the opposite side of the world. But North America has been moving west, so the longitude was probably significantly less than 180 degrees away. However, I’m not a geologist, so could be wrong here.

As Voyager says, early on there was thinking that Iceland may have been the spot. That’s because it happens that Iceland first started forming about the right time. Probably a coincidence, since there likely would be other evidence pointing to it. Even before Chicxulub was discovered, there were indications that the event happened in the Caribbean/Gulf of Mexico area.

Excellent point, which I should have thought of but didn’t. I wonder if there’s a site somewhere that lets you see where the landmasses where at any given point in the past?

What is the consideration of a Quasar-effect/Gamma-burst/uber-Xray-event that could have happened, yet not coincided with an impact event? Wouldn’t a 1-day/rotation under an extreme radiation not be possible to cause catostrophic devastation? Do Cosmic/Gamma/X rays leave a telltale signature? Alpha/Beta exposure over time cause death?

This article indicates that the Shiva impact crater off the coast of India may be the remains of the actual culprit, or at least fits the profile better than the one in Mexico.

Giant Impact Near India Not Mexico May Have Doomed Dinosaurs

There are several -this one is nice, I think (though there is no timeline). This one has a timeline but it requires you to register (and pay, I think) to view it all.