PDA

View Full Version : How sure are we that a meteor killed the dinosaurs?


WoodenTaco
04-10-2007, 08:42 PM
I remember when I was younger that the explanation for what caused the mass extinction which included dinosaurs was still up for debate, with the meteor hypothesis one among many. Today, it seems like it is referenced as fact, however. Is this just my own perception, or is it pretty much established that a meteor was the cause?

Leaffan
04-10-2007, 08:51 PM
It's a theory; a pretty damned good one from geological evidence, but only a theory.

Polycarp
04-10-2007, 09:11 PM
There's definite evidence that the impact at Chicxulub in the Yucatan (a) happened, (b) happened almost precisely at the K-T (Cretaceous-Tertiary) boundary, and (c) had widespread effects -- microscopic particles that are clearly impact fragments are embedded in the K-T boundary layers in what's approximately an accurate distribution pattern, diminishing with distance from the site in a ice-cream-cone shaped quasi-elliptical pattern with the long axis in what would have been downwind from the impact site as of the position of post-Cretaceous North America; the iridium spike that first alerted science to the possibility; etc.

It was therefore clearly highly likely to be a contributing factor to whatever events happened at the time, which included the third-greatest mass extinction in history.

There are other significant possible influences, notably a massive and longlasting volcanic upwelling in India (the "Deccan Traps"), and climate changes documented from protozoan and other planktonic deposits that may or may not have been the results of either or both the Chicxulub impact or the Deccan vulcanism. Dinosaur diversity, while still quite high, was also reduced in the latest Cretaceous, which may or may not have been a fourth causative factor or else early results.

Odds are high that the mass extinction resulted from a combination of all three factors. To say that Chicxulub in and of itself caused the dinosaurs to go extinct is something like saying that Gavrilo Prinzip caused World War I -- it may have been the single event that pushed things over the line, but was a part of a complex of events that worked together to cause the mass extinction.

DrDeth
04-10-2007, 09:20 PM
It was therefore clearly highly likely to be a contributing factor to whatever events happened at the time, which included the third-greatest mass extinction in history..

Right. Certainly A contributing factor, and perhaps even the biggest factor. But not the only factor.

Darwin's Finch
04-10-2007, 09:57 PM
I remember when I was younger that the explanation for what caused the mass extinction which included dinosaurs was still up for debate, with the meteor hypothesis one among many. Today, it seems like it is referenced as fact, however. Is this just my own perception, or is it pretty much established that a meteor was the cause?

It's largely a fact that the asteroid impact occurred, as mentioned. However, there are a couple things to keep in mind, both very important to understanding the event:

1) Dinosaurs as a group didn't actually go extinct. Many lineages did (but note that many also died out during the extinction events which mark the transition between the Triassic and Jurassic as well as the Jurassic - Cretaceous boundary), but birds, being direct descendants of dinosaurs survived the K-T extinction event. Birds are every bit as much dinosaurs as we are mammals.

2) Many varied groups went extinct, beyond the non-avian dinosaurs. Mosasaurs and plesiosaurs - two groups of marine reptiles - went extinct at the same time. Pterosaurs, marine invertebrates such as rudist corals and ammonites, even some groups of birds (e.g., enantiornithes and hesperornithiformes) all went extinct as well. In North America, several freshwater invertebrates (like snails), and marsupials also took major hits.

There were also, as noted above, several events occuring more or less simultaneously (in a geological sense): the asteroid impact in North America, the Deccan Traps in Asia, major seaway regressions and climate changes world-wide. Even then, how these macro events translate to the proximate causes of the various extinctions is not fully understood (for example, the asteroid impact itself probably did not really cause global extinctions, but very likely wreaked havoc in the western hemisphere, as a direct result of annihiliating anything at ground zero and indirectly from massive fires, debris clouds, and so on; with possible secondary and tertiary efects occurring world-wide). More than likely, certain groups succumbed to certain events in a relatively short time, rather than everything dying simultaneously to a single cause.

Colibri
04-10-2007, 10:24 PM
It's a theory; a pretty damned good one from geological evidence, but only a theory.

No, it was never a "theory" in the scientific sense, since it merely was an explanation for a single event. It was, and is, a hypothesis, and one that is pretty well supported by the evidence (although, as others have said, it may not have been the only cause).

"Only a theory" is pretty much meaningless in relation to science.