What if an asteroid didn't kill off the dinosaurs?

Factual Questions
21

Pantellerite

…erm, you are looking at 12.3Km[sup]3[/sup] compared to .35Km[sup]3[/sup]?

Its the power 3 that does that damage.

12.3[sup]3[/sup]/.35[sup]3[/sup] ,makes around 7500 times larger.

If I am using these terms incorrectly then I must bow to your greater knowledge.

On this site Laki kicks out around 14.71km[sup3[/sup] of basalt some sites have an upper figure of just over 15Km[sup]3[/sup]

http://volcano.und.nodak.edu/vwdocs/volc_images/europe_west_asia/laki.html

However this was not the main atmospheric concern, from here, mention is made of the Sulphur Dioxide emissions,

http://www.sciam.com/askexpert_question.cfm?articleID=000D4121-91C5-1CD1-B4A8809EC588EEDF

From here the scale of gaseous emission is put into perspective with the massive Mt Tambora event.

http://www.aber.ac.uk/iges/cti-g/STHAZARDS/icelandicvolcanoes/laki%20fissure%20eruption%201783.html

This was the largest eruption by total emissions in recorded history, with the possible exception of the enormous Santorini explosion and caldera collapse some 3500 years ago.

Other sites quote the total aerosol emissions at some 80 to 100 times that of Mt St Helens, so yes you are correct, but the total energy ouput from Laki was very much greater, not surprising since it took place over 8 months and for a few days the estimated lava flow rate exceeded that of water from the Amazon basin.

The total material released was thousands of times more then Mt St Helens, but since most of this stayed on Iceland, I guess I have to concede that the climate altering material, SO4 emissions is only 80 or 90 times.

22

erm?? The km is cubed, not the number of cubic kilometers.

Don’t do that. You’ll be bowing all day long. :slight_smile:

23

Very true, but I need to pick one nit. Sauropods were on the decline everywhere in the Cretaceous as opposed to their near dominance of large-herbivore niches in the Jurassic, but Alamosaurus was still a prominent part of the Cretaceous fauna in most major North American sites.

On the other hand, stegosaurs had become extinct in most of the world by the end of the Jurassic, and survived into the Cretaceous only on the island continent now known as India.

Ignoring the comments about Laki, the point about the Deccan and Siberian Traps is very important – it’s probably the single terrestrial (as opposed to asteroid-impact) cause most often advanced by reputable paleontologists. And many think that the eruption of the Deccan traps was the major cause of dinosaur decline, with the Chicxulub impact simply adding the coup de grace. (Barb and I went through the theories in detail as a part of her paleontology courses when she was taking her paleoanth. degree.)

As for what might have happened – it’s really hard to say. Dinosaurs had a firm hold on most large-animal niches prior to the 65mya extinction, but eutherians were just beginning to develop, and some fair-sized marsupials and primitive placentals were around in the Late Cretaceous, especially the last two stages. I suspect there would have been strong competition, with neither group having ascendancy – Africa might well have had mega-lions preying on ornithischians, South America raptors preying on litopterns.

24

What RM Mentock said. Start bowing!

A good point you make is that it is not so much how much is erupted, but what is erupted. My reference, Myron Best, goes on to say that although St. Helens and Chichon were nearly identical in size, St. Helens had negligible effect on climate, whereas Chichon–which erupted a considerable volume of SO2 and approximately 10[sup]13[/sup] g sulfuric acid into the atmosphere–cooled the northern hemisphere by about 0.5°C.

Also, as a petrologist/volcanologist, I tend to favor Catastrophism By Volcano, per Polycarp’s last post.

25

Well, of course, you would then, but don’t let all that bowing and scraping go to your head.

Have you seen Michael Rampino’s theory that the volcanism was caused by an impact at the antipodes? I think that was preceded by the theory that the volcanism was caused by an impact directly–some guys in Montana, right?

26

I haven’t heard of it, but I’ll look it up when I get a chance. Honestly, I don’t spend a lot of time thinking about the K-T event (I’m more geochemistry and T-Q oriented!), but the Deccan hot spot–cause of extinction or not–has (to me) never seemed any different from any other long-lived, mantle-plume induced hot spot on the planet that therefore requires some kind of special (impact) explanation.

27

Didn’t quite follow that–did you mean that mantle-plumes require impact explanations, or that they don’t and so why would any of them? I suspect the latter.

I think what Rampino has tried to do, is reconcile the two theories. In other words, the coincidence of the extinction, eruption, and impact is more than coincidence. He’s applied the theory to other extinction events, if I recall.

28

Yeah, sorry… on review that post could’ve been more coherent, but I was in a rush to get to class (I let 'em out a bit early).

What I meant was that hot spots don’t require impact origins, and that if we’re content for a mantle plume (being generated at the core/mantle boundary) origin for hot spots like Hawai’i, Yellowstone, et al., then why not the Deccan? I’m willing to accept that the Deccan eruptions may’ve triggered catastrophic climate change that led or contributed to the KT extinction, and that there was a large impact event at the KT boundary that also may’ve contributed to the KT extinction, but I seriously doubt that the two are related. If for no other reason than the fact that the Deccan eruptions–while spanning the KT boundary–did, in fact, begin during the Cretaceous long(ish, about 1.5 Ma) before the impact (Cite.).

29

Given the sparse remains (about five specimens total, as near as I can tell from a quick search), I think it’s difficult to say anything about the relative prominence of Alamosaurus in North America. Further, it is thought by many paleontologists to be an immigrant from South America, so it still appears that all native NA sauropods had gone extinct ~40my prior to the K-T event.

Of course, if you ask the “intrinsic gradualists”, they would say otherwise :wink:

30

If you want to see what dinosaurs might look like if they hadn’t become extinct, this is a great website:

http://specdinos.0catch.com :slight_smile:

Alamosaurus is only found in southern sites. Canada seems to have a real lack of Sauropoda.

Were sauropods really on the decline? It does look like there was a loss of sauropod diversity by the Late Cretaceous, possibly with only Titanosauridae remaining, but it looks like most parts of the world at least had some sauropods right before the end of the Cretaceous. Saltasaurus and Neuquensaurus in South America, Magyarosaurus in Europe, Rapetosaurus in Madagascar, Titanosaurus in India, Opsithocoelicaudia in Mongolia, etc.

Are you referring to Dravidosaurus? Isn’t that one now considered a non-dinosaurian marine reptile?

31

We(I) are (am) not worthy,

Scrapes and bows.

32

It’s no sure bet the Dinos would have gone extinct even without the meteor impact. These were the dominant creatures on earth and they came in a myriad of sizes, shapes and adaptations. A simple, gradual change in climate would have been very unlikely to have wiped them off the earth. In fact they had survived changes in climate before. It would have taken something truly catastrophic to dislodge every single species of the dinosaurs at once (as well as all the plesieosaurs, mososaurs, icthyosaurs, pterosaurs, etc…). If they had made it past the impact, they very well would still be around today, of course todays dinosaurs would be very different from the ones that thrived during the Cretaceous.

Mammals would likely have continued to be little pests scurrying around at the margins.

33

I must nitpick…
Birds did not evolve from “dinosaurs” they evolved from a certain species of dinosaur. They are not T-rex and triceratops decendants.

34

Nitpicky equivocation: I said “the single terrestrial cause … most often advanced…” The gradualists, understandably, do not advance any single cause, terrestrial or otherwise! :slight_smile:

35

There was a speculative TV series based on this very premise in the '60s.

It was called The Flintstones. :slight_smile:

36

Why not? Once again: Most species of dinosaur were long extinct before the terminal Cretaceous.

37

Weren’t most species of dinosaurs extinct before the start of the Cretaceous? OK, maybe a lot?

38

Most species of Mammals were extinct before the Ice Age, too. “In the long run, we are all dead.”

Modern analysis of dinosaurs shows a bunch of predominantly megafauna very well adapted to their econiches, with quite good potential for long-term survival. Obviously, specific species, genera, and even families died off before the K-T event, whatever it was. But most did not. Of the dozen or so infraorders into which the two groups of dinosaurs are traditionally divided, only the Stegosauria were extinct.

BTW, the references I had did not give a specific genus but did indicate that there were stegosaurs in India during the Cretaceous – if that was based on Dravidosaurus and it has since been reinterpreted, I’ll have to retract that comment, with gratitude for the correction, Sauroposeidon. Would you perhaps have more information on this?

39

No, I don’t know anything more about it. Just what is here:

If there are true Indian stegosaurs, they haven’t been named yet.

40

The following cites are given for Chatterjee’s reassignment of Dravidosaurus material from a stegosaur to that of an unidentified plesiosaur:

Chatterjee, S. & Rudra, D. K., 1996. “KT events in India: impact, rifting, volcanism and dinosaur extinction,” in Novas & Molnar, eds., 1996: 489–532.

Novas, F. E. (not A.) & Molnar, R. E., eds., 1996. Proceedings of the Gondwanan Dinosaur Symposium, Brisbane, Memoirs of the Queensland Museum 39(3): iv + 489–731 [December 20, 1996].

I haven’t read the article in question, so I don’t know any further details.