...and I can take you out of it." Remember that old parent's words of...well, if not wisdom, certainly effectiveness? Well, it may turn out that an asteroid brought dinosaurs into being. Guess it just shows that, either way, you shouldn't mess with Ma Nature.

I've observed before how insular paleontology and geology can be, and how hard it was for Alvarez to get his theory accepted, because earth scientists couldn't (or didn't want to) imagine extraterrestrial events having such an impact (literally) on the evolution of the planet and his life. The fact that this theory seems to be taken seriously shows that we've started to get over that.

Oh, and because I'm reading an interesting book on the subject, extra points to anyone who knows who Wilkes Land is named after, without looking it up (and no, "Wilkes" is not a sufficient answer).

All life may be from space...
I found this article and was amazed it has not gotten more press...
http://www.cnn.com/2006/TECH/science/06/02/red.rain/index.html

Alvarez did have one other problem in getting his impact theory accepted: he was a rude, arrogant s.o.b. who had a deep-seated contempt for the paleontologists, and didn't bother to hide it. The "controversy" consisted (and still consists -- it isn't fully settled by any means) largely of geologists and palaeontologists raising questions and objections about the Alvarez impact theory, and Alvarez and his supporters replying "sit down and shut up, we're the real scientists here and we're telling you what happened." Even today, supporters of the "asteroid doomsday" scenario simply refuse to address the weaknesses in the theory -- such as, why was the K-T extinction so incredibly selective? Certain taxa were wiped out completely (dinosaurs, pterosaurs, marine reptiles, enantiornithine birds), while other taxa that filled similar niches (sharks, freshwater reptiles, ornithurine birds) soldiered on.

Comodore Wilkes was the comander of the USS Vincennes and the cryptically named, US Exploring Expedition. He was likely the actual discoverer of Antarctica.

The US Exploring Expedition was one of the first Govt. financed scientific oceanographic expeditions quite groundbreaking as far as its methods and forshadowed some of the techniques used in the UKs monumental Challenger expedition of the 1870s.

Wilkes was a capable officer but was socially inept. His abrasiveness contributed to the expeditions lack of fame, but the expedition is now generally recognized as quite important in the history of oceanography.

Without looking it up I don't have the dates.

The important nickel and PGE deposits at Sudbury are now believed to be cumulates that formed as thick impact melts solidified over hundreds of thousands of years. This impact is even bigger, so the deposits may be even thicker (assuming they haven't be scraped away by glaciers.) Pity about the mile of ice and inhospitable international regime.

Pity about the mile of ice and inhospitable international regime.

I suspect the latter will be a much bigger barrier to their use than the former. It will probably be easier to get them from asteroids, judging by the ANWR experience. Which is good for prospects for space development, albeit dumb.

get them from asteroids

Or from the moon. The impact melt cumulate process should operate there as well, at least for large impacts, although it would be slower due to the lower gravity.

"Even today, supporters of the "asteroid doomsday" scenario simply refuse to address the weaknesses in the theory -- such as, why was the K-T extinction so incredibly selective? Certain taxa were wiped out completely (dinosaurs, pterosaurs, marine reptiles, enantiornithine birds), while other taxa that filled similar niches (sharks, freshwater reptiles, ornithurine birds) soldiered on."

Irrelevant. That alleged weakness does not go to the heart of Alvarez's discovery. It is factual that the Earth was hit at the extinction time and it is well supported that the consequence of such an impact would devestate the biosphere.
It is for the BIOLOGICAL scientists, not physicists like Alvarez, to hypothethize about 'why' some species survived and others died. That's their problem to solve, albeit a more intractable one given its complexity.

Indeed. The skeptics would have us believe it was just a coincidence that the impact occurred right on the K/T boundary, within very tight error bars, as demonstrated by the way many foram lineages went extinct right at the impact.

It's the sign of a winning theory that it can predict additional evidence, and also when evidence is bad. The impact theory predicted osmium in the impact layer would have chondritic rather than crustal isotope abundances; it did. It predicted iridium would be found on continents, not just in oceans; this was found. It predicted shocked minerals; found. It predicted no survival of extinct species past the impact layer; this held up (when bioturbation and similar mixing was taken into account). It predicted a massive impact crater would be found at the boundary; this was found.

Ammonites had been presented as a contrary to the impact theory, since they were thought to have gone extinct several million years earlier. But this turned out to be due to inadequate sampling and ecological changes at the single site near the boundary; later, ammonite fossils were found elsewhere right near the boundary, consistent with catastrophic extinction at the time of the impact.

I think some of the older Alvarez's arrogance was just from being a physicist, and a very smart guy. The standards of evidence in physics are apparently quite a bit higher than in paleontology. I also imagine the paleontologists didn't like having their noses rubbed in the inadequacy of their methodology. There was shoddy argumentation that (for example) ignored the fact that fossils of infrequently found organisms will, by chance, appear to go extinct well before they actually did (the Signor-Lipps effect).

philw wrote: "It is factual that the Earth was hit at the extinction time "

True.

"and it is well supported that the consequence of such an impact would devestate the biosphere."

False. The fact of the matter is this: there is no confirmed evidence the impact had any effect on the biosphere at all. The connection is assumed because the impact appears to immediately precede the extinction. The Alvarez theory as it's usually presented to the public is a gigantic "post hoc ergo propter hoc" fallacy!

Proof? Consider this: The impact occurred at Chicxulub, in Mexico. Alvarez himself stated that the effects would have been worst in North America. But a thorough survey of the only detailed K-T land fossil record in North America, the exposures of the Hell Creek region in Montana, demonstrated that among lower land vertebrates (meaning freshwater fish, amphibians, snakes, lizards, turtles, crocodilians) there wasn't any mass extinction at all. See Dr. Laurie Bryant's doctoral thesis, NON-DINOSAURIAN LOWER VERTEBRATES ACROSS THE CRETACEOUS-TERTIARY BOUNDARY IN NORTHEASTERN MONTANA, available via Amazon.com. Dinosaurs, gone. Pterosaurs, gone. Primitive birds, gone. Advanced birds, badly hurt. Every land animal bigger than about ten kilograms died. But a thriving ecosystem of lower vertebrates survived effectively untouched, precisely where the impact's effect was supposed to be the worst. And of course, the survival of this vertebrate ecosystem requires the survival of healthy populations of plants and invertebrates, to form the lower layers in the ecological pyramid.

The Alvarez theory cannot explain this. Nor can it explain why four out of the five largest extinctions in the fossil record are associated closely with the four largest episodes of basaltic lava flows in the geologic record. The K-T extinction occurred within the timeframe of the Deccan Traps. The Permo-Triassic extinction coincides with the Siberian Traps. The terminal Triassic extinction coincides with the gargantuan Central Atlantic Magmatic Province flows. And the terminal Devonian extinction sequence coincides roughly with a series of basalt flows in the Ukraine.

There's more to this matter than meets the eye. The basic, oft-repeated hypothesis of "asteroid impact --> global ecological devastation and mass extinction" simply doesn't work.

Alvarez himself stated that the effects would have been worst in North America. But a thorough survey of the only detailed K-T land fossil record in North America, the exposures of the Hell Creek region in Montana, demonstrated that among lower land vertebrates (meaning freshwater fish, amphibians, snakes, lizards, turtles, crocodilians) there wasn't any mass extinction at all.

Do you have a problem with logic? Those two assertions aren't inconsistent! For them to be inconsistent, you'd have to demonstrate that these kinds of species did worse elsewhere. Alvarez wasn't saying that everying in North America would be destroyed, only that the effects in NA would be worse than places farther away.

The Alvarez theory cannot explain this.

The Alvarez theory doesn't attempt to explain it. Nor does it have to! Do the Flood Basalt theories explain it? No? Then stop being hypocritical, 'mkay?

At least the Alvarez theory does a better job of explaining what happened than the Miracle Coincidence Impact Right At The Boundary But We Don't Believe in Catastrophes theories from what was the geologic mainstream. The alternative theories have far less explanatory power, with lots more handwaving, but apparently the anti-impact people are ok with that.

Alvarez was also responsible for discovery of the Alvarez effect: Later rediscovered by mere chemists searching for cold fusion.

Paul Dietz wrote: "Alvarez wasn't saying that everying in North America would be destroyed..."

Actually, Alvarez did say exactly that in his book T. rex and the Crater of Doom. Quoting from p. 13:

Where only the day before there had been fertile landscapes, full of plants and animals of all kinds, now there was a vast, smoldering netherworld, mercifully hidden from view by black clouds of roiling smoke.

In the next couple of pages he gives other images of the impact's effect on North America: "continent-size wildfires" and the lower half of the continent being reduced to "a desolate wasteland of the most appalling, agonizing destruction." There is no way that the Hell Creek ecosystem could have survived this scenario intact. But it did survive. QED, Alvarez's scenario is wrong.

Oh, one other thing to keep in mind: I haven't said anything about what theory I think is right -- because I don't think any of the currently-offered theories are right. I mentioned the basalt flows for two reasons: first, to demonstrate that there's another fact in the record that stinks of "this ain't no coincidence!" at least as strongly as the impact does; and second, to counter the idea that there must be a cause-and-effect connection between the impact and the extinction simply because they're so close together in time. The time correlation is just as good for the volcanic eruptions. If you don't accept the 'post hoc ergo propter hoc' reasoning for the volcanism theory, then why accept it for the impact theory?

OK, so maybe the K/T impact wasn't the only reason for the mass extinction. Maybe in some cases it was the final straw for dozens of species already on the brink for other reasons, notably the Deccan Trap eruptions.

But the real central message is that asteroids are dangerous, and that sooner or later, unless we do something about it, another K/T impact will occur, and will cause an uncertain but very large amount of damage to the ecosystem.

The only remedy to this is to develop the capacity to push the thing out of the way, or preferably to mine it into nothing before it arrives.

I would rather that asteroidal platinum-group metals arrive in small controlled packages, thank you very much.