PDA

View Full Version : Whew! Asteroid impacts not as dangerous as thought



ToSeek
2002-Jan-24, 01:43 PM
The K-T impact extinctions: Dust didn't do it (http://www.spaceref.com/news/viewpr.html?pid=7210)

So an asteroid impact would only kill a billion of us, not everybody.

The Curtmudgeon
2002-Jan-25, 08:37 PM
Ah, that's okay then--just the astrophysical equivalent of one-second-slum-clearance (q.v. Heinlein's "The Door into Summer", f'rinstance). /phpBB/images/smiles/icon_smile.gif

More seriously, this is an example of one of the major problems with the evolutionary theory [ducking hurled brickbats while still typing quickly /phpBB/images/smiles/icon_razz.gif ], in that the Bio side bases their ideas on what they think they know about Geo/Astro/Whatever, while the Geo guys are moving ahead based on what they think they know about Astro/Bio/Whatever, and the Astro guys also have what they believe to be a handle on the other five aspects of the elephant. But when they start talking to one another at length and in detail, they find out that "Hey, wait a minute, you can't assume that--it doesn't work that way!"

(Having said that, I will point out that the fact that the real scientists involved, although that seldom includes the textbook writers, do eventually have these little get-togethers where everybody swaps notes is Really Good Science, and I'm glad to see it happening here.)

But the biggest problem with the whole K-T Dinosaur Killer theory has been that the most plausible scenario invoked for it, the photosynthesis-stopping dust cloud, wouldn't have been as selective as the fossil record indicates: there are too many species, both plant and animal, that survived the K-T impact essentially unchanged. I'm glad to see that the scientists are now admitting this hole in the theory and looking for ways to fill it in (or, more likely to my way of thinking, patch it over).

And please note, I am not writing this primarily to inject my thoughts vis-a-vis evolution into the discussion, just to point out that the problems of the K-T Dino-Whacker have been appreciated for a long time in certain fields, without anyone taking any visible steps to address them, which even (or especially!) if you accept evolution whole-heartedly, is Bad Science. But everybody, by and large, has just been going the route, saying, "Oh yes, we've pinpointed the crater of the asteroid that whacked the dinos, so that's all well-established now and we can move on to other things." But the Dino-Whacker, as thought of up to now, doesn't work to explain what is really found in the fossil record when you look at the whole breadth of it, it only accounts for the disappearance of the dinos and a few other phyla without explaining why so very many others didn't die out on cue.

I'm reminded, somewhat at a stretch, of one of my favourite Irish jokes (note: I'm allowed to tell Irish jokes because I'm one myself--well, okay, half-Irish by ancestry). Bear with me, it's a little rambling, but I really do have a point to make with it:

So this reporter from the BBC is out on assignment, polling people to find out what they think is Mankind's Greatest Invention. He's on his way back to London, and passes this Irish navvy (road labourer) and thinks, "Hah! I'll ask him, he'll say something like 'the shovel' or 'the pick'!" So he stops, and calls the navvy over and asks, "M'man, what do you think is Mankind's Greatest Invention?" The navvy starts thinking, and a couple of hours later says, "The vaccuum flask [Thermos bottle to USans]". This completely throws the reporter for a loop, and he asks "The vaccuum flask?? Why the vaccuum flask?" "Sure," says the Irishman, "it keeps hot things hot, and it keeps cold things cold!" "Well, yes, but what's so great about that?" Replies our man, "How does it know?"

[Note to any PCists who happen to stop by: you can read the joke as the Irishman having fun at the Londoner's expense, it's just as funny that way. /phpBB/images/smiles/icon_smile.gif ]

Hopefully, you see what I'm driving at here: how did the Dino-Whacker "know" to just wipe out the phyla and species that it did, while having little or no effect on so many others? The obvious but trite answer is that it didn't know at all, but you still have to explain why its affects were so very different in different cases, and that's not been done. Until the theories account for all of the fossil evidence, they're not Good Science (or at least, no better than Halfway Good Science).

Yeah, I know you're just waiting to pummel me as a backwoods Creationist; go ahead, but try to address my scientific point about what evolutionary science leaves out or ignores, please, and not just lambast me for believing things I read in a Good Book.

The (you may fire when gridley, Ready!) Curtmudgeon

James
2002-Jan-25, 10:08 PM
On 2002-01-25 15:37, The Curtmudgeon wrote:

But the biggest problem with the whole K-T Dinosaur Killer theory has been that the most plausible scenario invoked for it, the photosynthesis-stopping dust cloud, wouldn't have been as selective as the fossil record indicates: there are too many species, both plant and animal, that survived the K-T impact essentially unchanged.

Okay, how about this scenario: the asteroid slams into the Chuxalub(or what would become the Chuxalub) area. IIRC, about that time in Earth's history, the continents were almost where they are now, and there really wasn't a Yucatan Penninsula as we now know it. In other words, the asteroid hit in the middle of the pre-historic Gulf of Mexico. As we all know, when an asteroid hits water, you have more trouble than when it hits land, right? So, it hits. You got: tsunamis, earthquakes(the asteroid is about 5-6 miles across; you know it's gonna hit the bottom of the sea), blast cloud, debris falling everywhere, etc. You know that any and everything within a good area around the blast crater is gonna be gone, that's almost a given. I'd say that the Americas felt the brunt of the blow from the asteroid. The rest of the world? I don't know. All I know is that you have the earthquakes and tsunamis going everywhere from the impact crater and that the tsunamis had to have reached for several miles inland, given the chance. Maybe the asteroid and/or the earthquakes which happened as a result of the asteroid stirred volcanoes to erupt where none had been before or even caused some eruptions to be even more intense than otherwise.

Anything else, I don't know. You wouldn't happen to have a time machine I could borrow?


...if you accept evolution whole-heartedly...

I don't know if this is an attack on evolution, but I'll tell you this: evolution ain't perfect. If a scientist says it is, smack him/her upside the head. They're wrong. Granted, we've only known about dinosaurs just a few decades longer than evolution, but no one ever said either theory was perfect. /phpBB/images/smiles/icon_biggrin.gif

_________________
"It is possible to store the mind with a million facts and still be entirely uneducated." -- Alec Bourne

<font size=-1>[ This Message was edited by: James on 2002-01-25 17:09 ]</font>

The Curtmudgeon
2002-Jan-26, 12:48 AM
On 2002-01-25 17:08, James wrote:
Okay, how about this scenario: the asteroid slams into the Chuxalub(or what would become the Chuxalub) area. IIRC, about that time in Earth's history, the continents were almost where they are now, and there really wasn't a Yucatan Penninsula as we now know it. In other words, the asteroid hit in the middle of the pre-historic Gulf of Mexico. As we all know, when an asteroid hits water, you have more trouble than when it hits land, right? So, it hits. You got: tsunamis, earthquakes(the asteroid is about 5-6 miles across; you know it's gonna hit the bottom of the sea), blast cloud, debris falling everywhere, etc. You know that any and everything within a good area around the blast crater is gonna be gone, that's almost a given. I'd say that the Americas felt the brunt of the blow from the asteroid. The rest of the world? I don't know. All I know is that you have the earthquakes and tsunamis going everywhere from the impact crater and that the tsunamis had to have reached for several miles inland, given the chance. Maybe the asteroid and/or the earthquakes which happened as a result of the asteroid stirred volcanoes to erupt where none had been before or even caused some eruptions to be even more intense than otherwise.

But a big part of the problem is that the extinctions seen in the fossil record weren't limited to any particular area of the world, but were limited to particular phyla all over the world! I can see how your scenario would cause mass extinctions in a particular area, such as the Americas or even just North America, but the tsunamis wouldn't reach the Pacific. (Unless it's postulated that North and South America were physically separated at the time, i.e. the Panama Isthmus was a strait. This idea does feature in explanations why South America grew some very distinctive animals for a while, but that is all dated much later than K-T, into the earliest Pleistocene IIRC. But even with a Panamanian Strait at the time of K-T, it would be too narrow for much of a tsunami to propagate through, and what little did get through would dampen down long before it reached Asia, or even the Pacific islands.) I doubt any such tsunamis would even reach the Indian Ocean, although of course there's much more open ocean connecting the Atlantic and Indian Oceans than the A & P.

A mantle-level shock wave, of course, could propagate whether there's an isthmus or strait at Panama, but again there's the question of how it could cause phyla-specific extinctions. It's a much better candidate, IMHO, than the Dino-Whacker, since effects would be more local in scope, but it still leaves questions.


Anything else, I don't know. You wouldn't happen to have a time machine I could borrow?

Well, my first priority when I get my time machine up and working is to go kill Alexander Graham Bell (and probably Watson, too, just to be safe). But after that, we can see about a loan. /phpBB/images/smiles/icon_biggrin.gif



...if you accept evolution whole-heartedly...

I don't know if this is an attack on evolution, but I'll tell you this: evolution ain't perfect. If a scientist says it is, smack him/her upside the head. They're wrong. Granted, we've only known about dinosaurs just a few decades longer than evolution, but no one ever said either theory was perfect. /phpBB/images/smiles/icon_biggrin.gif

That particular statement wasn't meant as an attack on evolution, just pointing out that my particular objection in this post shouldn't be rejected out-of-hand, just because I'm a Bible-thumping Creationist.

But many scientists, so called, do indeed insist that questioning evolution is Evil and Not Scientific and so on; if you raise any questions or objections at all you're immediately tarred with the "Creationist!!!" label, even when said questions have nothing to do with Genesis or any interpretation thereof. In my case, of course, the label is correct in and of itself, but too many scientists slap the label on the objections as being Creationist, rather than believing that anyone who reads and believes the Bible can actually ask scientific questions and raise scientific objections. This has been shown time and again in the evolutionary literature, to the point where I have read of a number of biologists who feel that they are stifled, because they don't want to publish in "Creation Science" journals (not being Creationists of any sort), but their non- or even anti-Neo-Darwinism articles are branded as such (that is, as "Creation Science") and dismissed before being given a fair reading in peer-reviewed science journals.

Anyway, we're in danger of turning this into a general evolution discussion, or diatribe if you will /phpBB/images/smiles/icon_smile.gif , which is neither my point nor within the rules of the BABB. I guess I was just pointing out that the article in the first link is unusual in that it agrees that the Dino-Whacker theory has problems, which I find unusual but good. To keep this conversation from going totally beyond the bounds (and I admit it's my own earlier post that started leading off-topic), we should keep ourselves to a discussion of how the Dino-Whacker, assuming it to have existed, could have accounted for the extinctions found in the record. Unfortunately, that puts me at a loss because I fail to see how it could explain them. But I'm more than willing to read other people's opinions and scenarios, as long as they don't mind my attempts to pick holes in them. Yours is a good start, James, but I don't see that it can cover the ground fully either.

The ("K-Mart shoppers! We have a Blue Light Special on Dino-Whackers on aisle 9!") Curtmudgeon

Donnie B.
2002-Jan-26, 01:39 AM
The notion that the K-T extinction was caused by an asteroid or comet impact is relatively young, and there's still a lot of uncertainty. However, do remember that it was not accepted immediately; indeed, it was rather scorned by paleontologists at first.

But now it's the prevailing theory (not accepted universally, but widely). The only way that could happen is if it has lots of good evidence and explanatory power.

One detail I've heard is that the Yucatan impact happened to hit an area where the rocks were rich in a specific substance (for the life of me I can't recall what it is; not iridium; that's the marker that shows the event was an impact, but it would be present in any such impact. Strontium, perhaps?)

The presence of this contaminant in the dust cloud is responsible, in this refinement of the theory, for the especially "deadly" nature of the impact. This also explains why other impacts of similar size were not accompanied by mass extinctions.

As to the spotty nature of the extinctions, we have to keep in mind that such a catastrophic event has many effects, global and local; the fate of any one microenvironment is highly contingent. For instance, a particular phylum can be destroyed by a drastic drop in its (collective) food species; those food organisms may eventually recover from a small fraction of surviving individuals, but the predatory group is gone forever.

One piece of evidence for this scenario is the rise of giant birds and mammals that moved into niches previously filled by various dinosaurs; the underlying ecosystem recovered, and another species evolved to exploit the top predator's role.

But it's quite true that there are many unanswered questions about the K-T extinctions. The research is very much an ongoing concern.

lpetrich
2002-Jan-26, 07:19 AM
I'm still sure that the asteroid impact is the ultimate cause of the dinosaurs' extinction, whatever intermediate causes there had been. In fact, that dust debunker stated that "he believes it may have been sulfate aerosols produced from impacted rocks and soot from global fires that could have shut down photosynthesis and caused global cooling."

Hypothesis which deserve to be tested, of course.

lpetrich
2002-Jan-26, 07:34 AM
The Curtmudgeon:
More seriously, this is an example of one of the major problems with the evolutionary theory [ducking hurled brickbats while still typing quickly /phpBB/images/smiles/icon_razz.gif ], in that the Bio side bases their ideas on what they think they know about Geo/Astro/Whatever, while the Geo guys are moving ahead based on what they think they know about Astro/Bio/Whatever, and the Astro guys also have what they believe to be a handle on the other five aspects of the elephant. But when they start talking to one another at length and in detail, they find out that "Hey, wait a minute, you can't assume that--it doesn't work that way!"


And what's your point? The most that you've demonstrated is that interdisciplinary cooperation can be difficult when one has to master the arcana of several different fields. I don't see how that discredits research into biological evolution in general, which is what you are trying to imply.



The Curtmudgeon:
But the biggest problem with the whole K-T Dinosaur Killer theory has been that the most plausible scenario invoked for it, the photosynthesis-stopping dust cloud, wouldn't have been as selective as the fossil record indicates: there are too many species, both plant and animal, that survived the K-T impact essentially unchanged. I'm glad to see that the scientists are now admitting this hole in the theory and looking for ways to fill it in (or, more likely to my way of thinking, patch it over).


The most you've demonstrated is that one ought not to jump to simplistic cause-and-effect conclusions. I'm sure that that impact is the ultimate cause of the K-T mass extinction, because it would otherwise be an extreme coincidence. However, that says little about intermediate causes, like what that meteorite's impact injected into the atmosphere and the vegetation fires that it caused; these will have to be researched more carefully.

lpetrich
2002-Jan-26, 08:10 AM
There is actually a simple way of surviving asteroid impacts, or at least those elsewhere on one's home planet: lay low until the dust/haze/soot settles. The next step is to consider what species could easily have done so.

For land plants, it's practically a no-brainer, since many species' seeds can stay dormant for months or years if well-preserved by cold or dryness. In fact, many species of plants do not survive their first production of seeds, as many gardeners undoubtedly know (annual vs. perennial plants). An alternative way of surviving is to drop the leaves during a dry or cold season and regrow them from food supplies stored in roots when conditions improve again. And some plants are adapted to toughing out cold weather; for example, cold-climate evergreen trees.

This strategy can be pursued by land animals to varying degrees; the animals can slow down or enter a long sleep (hibernation/aestivation). Cold-blooded animals like turtles and lizards can easily slow down; warm-blooded ones have to be specially adapted to do so, and are generally not. This could easily account for the demise of the dinosaurs, since if they were warm-blooded, they would have needed to continuously eat, and losing much of their food would mean quick starvation. However, that makes the survival of birds and mammals a mystery, since they are also vulnerable to food-supply interruption. However, most of the mammalian survivors, and probably many of the avian ones, were relatively small, mouse-sized to cat-sized. Reduction in food supply may have simply meant a reduction in population, without outright extinction, at least for generalist species.

However, for this mechanism to work, much of our planet must have had slowed rather than stopped plant growth if the haze had lasted for several months. However, if the haze was partially transparent, then some light would have gotten through and allowed plants to do a limited amount of growth.

We now go from the land to the water.

For marine algae, especially microscopic algae, life is much more difficult, since they cannot store much food, and since they may be very temperature-sensitive.

As to marine animals, they are dependent on those algae, though often very indirectly; marine food chains can have several levels. Thus, if the algae start dying, they will cause their eaters to start dying, and so on up the chain. Also, the eaters can be temperature-sensitive, making them additionally vulnerable.

GrapesOfWrath
2002-Jan-26, 11:34 AM
On 2002-01-26 02:34, lpetrich wrote:
The most you've demonstrated is that one ought not to jump to simplistic cause-and-effect conclusions. I'm sure that that impact is the ultimate cause of the K-T mass extinction, because it would otherwise be an extreme coincidence.
So, what would the timing of the eruption of the vast Deccan Traps mean? Would that be just an extreme but inconsequential coincidence?

Donnie B.
2002-Jan-26, 01:03 PM
OK, what follows is pure speculation, but...

Could the Yucatan impact have triggered the eruption of the Deccan Traps? Maybe the K-T extinction was a one-two punch.

When you consider that the Traps are almost directly opposite the impact site, things get even more interesting.

Has anybody modeled the shock waves resulting from a big impact? Could there be a lensing effect that produces amplification of the shock opposite the impact?

If the Traps were in a "state of readiness", maybe the impact set them off, or multipled smaller eruptions that were already underway. That led to a second source of dust and particulates that completed the job the asteroid started.

[/speculation]

Kaptain K
2002-Jan-26, 01:07 PM
I wish I could remember where I read it, so I could give a link or source, but it has been hypothesized that since the Deccan Traps are nearly antipodal to the impact site, it could be direct cause and effect.

Donnie B.
I was composing this when you posted. It is not a reply to you. Perhaps a confirmation.
_________________
TANSTAAFL!

<font size=-1>[ This Message was edited by: Kaptain K on 2002-01-26 08:12 ]</font>

Donnie B.
2002-Jan-26, 01:09 PM
Ahhh! Sulfates!

I do believe that's the substance that's enhanced in Yucatan rocks, and why that impact site was so unlucky. In this scenario, the vaporized sulfates produced the mother of all acid rains, damaging plant life directly, and altering the Ph balance of the oceans and fresh water lakes and streams.

I'll look for a link if I have some time this weekend.

[Later...]

Found a couple of decent references on this theory. The first is a research paper (relatively easy to follow), the second a more general, popular overview.

http://www.google.com/search?q=cache:6Re6AyPMICcC:www.lpi.usra.edu/meetings/lpsc97/pdf/1790.PDF+Chicxulub+sulfates&hl=en

http://neo.planetary.org/SocietyProjects/Belize/BelizeGeology.html


<font size=-1>[ This Message was edited by: Donnie B. on 2002-01-26 08:17 ]</font>

GrapesOfWrath
2002-Jan-26, 07:45 PM
On 2002-01-26 08:07, Kaptain K wrote:
I wish I could remember where I read it, so I could give a link or source, but it has been hypothesized that since the Deccan Traps are nearly antipodal to the impact site, it could be direct cause and effect.
This idea was written up in a 1/5/95 article in Time magazine (http://www.time.com/time/magazine/archive/1995/950109/950109.science.html), so you may well have read it there. It attributes the idea to Hagstrum and Boslough. My advisor was working on antipodal detection of earthquakes, so I had the same idea early on. When I read the Time magazine article, I called Boslough. Turns out he was an undergrad at Caltech when my advisor was a graduate student there--and had also got the idea from him!

Michael Rampino, Ken Caldeira, Duncan Steel, and many others have worked on the idea. Part of the genesis of the idea is the antipodal nature of a large impact on Mercury and its Caloris basin (http://www.cmnh.org/fun/dinosaur-archive/1995Feb/0360.html).

James
2002-Jan-27, 03:37 AM
On 2002-01-25 19:48, The Curtmudgeon wrote:


On 2002-01-25 17:08, James wrote:
Okay, how about this scenario: the asteroid slams into the Chuxalub(or what would become the Chuxalub) area. IIRC, about that time in Earth's history, the continents were almost where they are now, and there really wasn't a Yucatan Penninsula as we now know it. In other words, the asteroid hit in the middle of the pre-historic Gulf of Mexico. As we all know, when an asteroid hits water, you have more trouble than when it hits land, right? So, it hits. You got: tsunamis, earthquakes(the asteroid is about 5-6 miles across; you know it's gonna hit the bottom of the sea), blast cloud, debris falling everywhere, etc. You know that any and everything within a good area around the blast crater is gonna be gone, that's almost a given. I'd say that the Americas felt the brunt of the blow from the asteroid. The rest of the world? I don't know. All I know is that you have the earthquakes and tsunamis going everywhere from the impact crater and that the tsunamis had to have reached for several miles inland, given the chance. Maybe the asteroid and/or the earthquakes which happened as a result of the asteroid stirred volcanoes to erupt where none had been before or even caused some eruptions to be even more intense than otherwise.

But a big part of the problem is that the extinctions seen in the fossil record weren't limited to any particular area of the world, but were limited to particular phyla all over the world! I can see how your scenario would cause mass extinctions in a particular area, such as the Americas or even just North America, but the tsunamis wouldn't reach the Pacific. (Unless it's postulated that North and South America were physically separated at the time, i.e. the Panama Isthmus was a strait. This idea does feature in explanations why South America grew some very distinctive animals for a while, but that is all dated much later than K-T, into the earliest Pleistocene IIRC. But even with a Panamanian Strait at the time of K-T, it would be too narrow for much of a tsunami to propagate through, and what little did get through would dampen down long before it reached Asia, or even the Pacific islands.) I doubt any such tsunamis would even reach the Indian Ocean, although of course there's much more open ocean connecting the Atlantic and Indian Oceans than the A & P.

A mantle-level shock wave, of course, could propagate whether there's an isthmus or strait at Panama, but again there's the question of how it could cause phyla-specific extinctions. It's a much better candidate, IMHO, than the Dino-Whacker, since effects would be more local in scope, but it still leaves questions.

I went to the Science Museum of Minnesota earlier today. They had and exhibit on the native cultures around the world. Anyway, I saw a map there from when National Geographic did their maps series some time ago, and it was a map of the continents as they moved over the globe over the history of the Earth. IIRC, the map they showed at the time of the K-T impact there was no Isthmus of Panama, but, look at where the asteroid impacted. It hit right on the inside edge of the(or what would become the) Yucatan Penninsula. You may have been right in that the tsunamis may have not gone to the Pacific, but I think that Donnie, lpetrich, and GrapesofWrath have covered the possibilities quite nicely. /phpBB/images/smiles/icon_smile.gif /phpBB/images/smiles/icon_biggrin.gif



Anything else, I don't know. You wouldn't happen to have a time machine I could borrow?

Well, my first priority when I get my time machine up and working is to go kill Alexander Graham Bell (and probably Watson, too, just to be safe). But after that, we can see about a loan. /phpBB/images/smiles/icon_biggrin.gif

You got a problem with Bell? May I ask why?




...if you accept evolution whole-heartedly...

I don't know if this is an attack on evolution, but I'll tell you this: evolution ain't perfect. If a scientist says it is, smack him/her upside the head. They're wrong. Granted, we've only known about dinosaurs just a few decades longer than evolution, but no one ever said either theory was perfect. /phpBB/images/smiles/icon_biggrin.gif

That particular statement wasn't meant as an attack on evolution, just pointing out that my particular objection in this post shouldn't be rejected out-of-hand, just because I'm a Bible-thumping Creationist.

Well, if you hadn't told me that you were, I probably would have had my suspicions, but I wouldn't have rejected your POV out-of-hand.


Yours is a good start, James, but I don't see that it can cover the ground fully either.

Who said it was supposed to? We just don't have enough evidence to postulate further nor can we hypothesize without knowing how things were in the Chuxalub area before the impact.


The ("K-Mart shoppers! We have a Blue Light Special on Dino-Whackers on aisle 9!") Curtmudgeon


LOL
That's a good one. /phpBB/images/smiles/icon_smile.gif

_________________
"It is possible to store the mind with a million facts and still be entirely uneducated." -- Alec Bourne

<font size=-1>[ This Message was edited by: James on 2002-01-26 22:39 ]</font>

David Simmons
2002-Jan-27, 04:16 AM
On 2002-01-25 15:37, The Curtmudgeon wrote:

More seriously, this is an example of one of the major problems with the evolutionary theory
Curtmudgeon


How would having the dionsaurs not wiped out by dust affect the Theory of Evolution by Natural Selection?

The disappearance of the dinosaurs would certainly affect the survival of every other species, but if they disappear, does it matter how?

<font size=-1>[ This Message was edited by: David Simmons on 2002-01-27 11:33 ]</font>

lpetrich
2002-Jan-27, 04:55 AM
The Chicxulub impact site is mainly limestone, meaning that an impact would produce a lot of carbon dioxide, which traps heat. However, sulfur would be present as an impurity, and a sulfuric-acid haze would reflect sunlight. Thus, the Earth would suffer first blocked sunlight and then some greenhouse heating.

Also, I'd like to clarify a hypothesis about the origin of the Deccan Traps that was presented here.

The planet Mercury has a big basin with concentric rings called Caloris; it is almost certainly a big impact crater that was filled in by resulting lava flows, just like the lunar maria. On the other side from it is some oddly-fractured terrain which appears to be the result of shock waves from that impact converging on that spot.

There is similar such fractured terrain on the opposite side from some lunar maria, notably Imbrium and Orientale, which suggests similar antipodal focusing.

And the Deccan Traps are hypothesized by some to be the result of antipodal focusing of seismic waves from the Chixulub impact. It would have created deep cracks, which would have allowed lava to escape.

However, back then, southern India was about 30 degrees off from Chicxulub's antipode. But it was off in longitude and not latitude, and its longitude is not directly observed, as its latitude and orientation are (paleomagnetism), but is instead inferred from its travel endpoints and from seafloor-spreading evidence. India had started as part of Gondwana and it ended by ramming into Asia, and if it had taken a more easterly route, it would have been right on target.

Here's a URL on the Moon connection (http://www.cmnh.org/fun/dinosaur-archive/1995Feb/0360.html)

GrapesOfWrath
2002-Jan-27, 05:08 AM
At the December 1993 American Geophysical Union meeting in San Francisco, Hiroo Kanamori presented a poster session about the effect of the impact of Shoemaker-Levi on Jupiter at the antipodal point.

Donnie B.
2002-Jan-27, 02:32 PM
I don't think it's absolutely necessary for the Deccan Traps to have been precisely antipodal to the Chicxulub impact. Assuming that they represent a place where the crust was already weak, or magma was already close to the surface, they might have been triggered into eruption even if they were close to, but not precisely at, the antipode.

As to the composition of the rock at the impact site, it has been (and is being) studied closely, and it is indeed rich in carbonates and sulfates. The possibility of intense, worldwide acid rain is a very intriguing one, and may help explain the pattern of extinctions.

GrapesOfWrath
2002-Jan-27, 02:41 PM
On 2002-01-27 09:32, Donnie B. wrote:
I don't think it's absolutely necessary for the Deccan Traps to have been precisely antipodal to the Chicxulub impact. Assuming that they represent a place where the crust was already weak, or magma was already close to the surface, they might have been triggered into eruption even if they were close to, but not precisely at, the antipode.
No, of course not, but in order to apply the physical theory, the Traps would have to have been a lot closer than what they appear to have been. Otherwise, we're just flinging out velikovsky-like events that may or may not have anything to do with one another. The possibilities have been seriously considered, but no one has yet come up with something that could reasonably satisfy the issue.

DALeffler
2002-Jan-27, 05:58 PM
I'm completely confused by the article linked in ToSeek's beginning post on this thread.

Doesn't the article say that global cooling resulting from the dust created by an asteroid impact (or sulfate aerosols from the same impact) is what smeared the dinos into the extinction files?

What I (the layman) read from the article is that even looking for Earth-orbit crossing objects is - "by far" - not nearly so important as it was before Pope's study: after all, how likely is it I'm gonna die in an airplane crash?

How likely is it I'd die in an airplane crash and how less likely is "by far"?

<font size=-1>[ This Message was edited by: DALeffler on 2002-01-27 13:03 ]</font>

lpetrich
2002-Jan-27, 08:00 PM
First, I think that ToSeek had misunderstood the article; he/she seems to think that the article was implying that the Sun was not obscured by anything when the artlcle clearly stated that a sulfate-droplet haze would have done the obscuring.

Also, doing a websearch for "fungal spike" uncovered several references to spikes in fungus-spore abundance that exactly correlated with various mass extinctions, notably the Permo-Triassic and the K-T one. This suggests that fungi must have had a feast at this time, which is consistent with the hypothesis of mass kills at P-Tr and K-T. I state "mass kills", because the death of individuals need not mean the end of a species (extinction); dying plants can be survived by their seeds/spores.

Fungal growth also suggests that much of the Earth stayed above freezing at that time, which is consistent with addition of both CO2, which heats the Earth, and some Sun obscurer(s) (dust/haze/soot) that kept light from reaching plants.

ToSeek
2002-Jan-28, 02:55 PM
On 2002-01-27 15:00, lpetrich wrote:
First, I think that ToSeek had misunderstood the article; he/she seems to think that the article was implying that the Sun was not obscured by anything when the artlcle clearly stated that a sulfate-droplet haze would have done the obscuring.


What's to misunderstand? I just provided a link and echoed (somewhat tongue-in-cheek) the thrust of the article that asteroid impacts may not be as deadly as once thought.

GrapesOfWrath
2002-Jan-28, 03:17 PM
I just want to know if you really are a he/she.

ToSeek
2002-Jan-28, 04:08 PM
On 2002-01-28 10:17, GrapesOfWrath wrote:
I just want to know if you really are a he/she.


Yes, I really am a he/she.

The Curtmudgeon
2002-Jan-28, 10:05 PM
On 2002-01-26 02:34, lpetrich wrote:
And what's your point? The most that you've demonstrated is that interdisciplinary cooperation can be difficult when one has to master the arcana of several different fields. I don't see how that discredits research into biological evolution in general, which is what you are trying to imply.

No, I'm stating that I believe evolution is discredited for reasons that I well know are not accepted by the majority of readers/posters on this site, nor do I expect them to be. I accept Genesis as fact, the vast majority here do not, and I know that I am limited to working within that framework.

The lack of good cross-field work doesn't discredit evolution itself, but it does call into question the reliance on the evolutionary scenario as beyond the point of being seriously questioned on a scientific basis. Too many people, and judging from what is published in the open press, even scientists put more reliance on NeoDarwinian evolution as basically proven beyond doubt than the scenario can justifiably bear once it is realised that many of the arguments are based on unsafe assumptions in fields beyond the normal scope of the various individuals.

I'll give a concrete example of what I'm talking about here (although this example has nothing to do with the Dino-Whacker). The earliest forms of life on Earth are (unless you accept Hoyle's Panspermia theory) supposed to have evolved in the ocean, due in part to its mixture of components (i.e., the ocean isn't just water + salt, as we all know). That's fairly taken for granted within the Biological circles--but trouble starts rearing its head when you realise that the Geology crowd have serious problems with the putative age of the ocean. It's simply not "salty" (in a general sense, not just NaCl) enough to have been around 4 billion years which the Bio crowd "need" for their scenario to play out and produce life. The geologists have measured rates of erosion and other processes which transport minerals, etc., into the ocean, and evaporation and other processes which concentrate the mineral content by leaching water out, and if these processes have been anything like constant at the levels we see today, the ocean couldn't possibly be anything close to billions of years old or else it would be much more highly saturated than it is.

Nothing in this prevents the biological theories of early-life evolution, or the geological theories of how the ocean formed, from being Good Science--but when you start building a "whole Earth" scenario which requires both, then you introduce problems because one points to 4 billion years and the other to a much lesser time span (IIRC, on the span of no more than several millions at the greatest stretch, although the accuracy of the data and the extrapolations from it are unclear). My point is that, in general, biologists don't realise that the geology implicit to their scenario doesn't work well based on what is seen today (and geology has, for various other reasons, been steadily moving away from Catastrophism for more than a century now, so that modern processes are supposed to mirror very well processes at all times in the Earth's history). Instead, when someone raises the point, they often get labelled (or libelled, if you will) as Creationists, because "everybody knows" that "only" the Bible-thumpers don't accept evolution.


The most you've demonstrated is that one ought not to jump to simplistic cause-and-effect conclusions. I'm sure that that impact is the ultimate cause of the K-T mass extinction, because it would otherwise be an extreme coincidence.

And you have some reason for believing that extreme coincidences can't happen?

And I note that your statement assumes that there even was such an impact. Yes, it's a generally-accepted assumption, and most theories regarding that era accept it rather than not (and I'm not even saying that it didn't happen), but it's still an assumption. What we have is what appears to be an ancient crater of a certain age, and certain aspects of it make it more likely that it is an impact crater rather than a volcanic crater, so the math is done to determine what would be the necessary object to cause such an impact crater, and voila, we have our Dino-Whacker. But there could be other explanations for it, and nobody (by necessity) ever observed the Dino-Whacker so it cannot be positively stated as the cause. And then, having this hypothetical impactor, scientists run the maths the other direction to see what would be the actual results of said impact, and the theory develops this Earth-encircling dust cloud of pulverised Yucatanium that blocks photosynthesis for a period of some years, and some books I've read have postulated some decades or longer. But that's where I say the problem creeps in: it's one thing for the geologists to say that this would be the result of the size and kind of impact we're discussing, and another thing for the biologists to say that this would then cause the dino extinctions because the effects of a world-wide stoppage of photosynthesis for any appreciable length of time would have even greater fallout (pun intended) than that, which we don't see in the fossil record.


However, that says little about intermediate causes, like what that meteorite's impact injected into the atmosphere and the vegetation fires that it caused; these will have to be researched more carefully.

That's more along the lines that I'm trying to keep this discussion to: what other explanations, instead of a world-wide halt to photosynthesis, could be justifiably proposed to connect the impact of a Dino-Whacking asteroid with the actual whacking of the dinos? Stopping photosynthesis as a mechanism is using Fat Boy on an ant hill; you'll certainly not have ant problems anymore, but that'll be the least of the effects you will get. Instead, can we see any reasonable basis for, perhaps, the impact causing a change in the composition of the atmosphere which was taken in by the dinos and other whacked groups and killed them off (collective asthma?) while having lesser or other effects on other groups to explain why they didn't disappear? If the asteroid did lay down a marker level of iridium as seems to be the case, could it also have raised the iridium level in the atmosphere for some period of time, and could that have had effects that explain the observed pattern of extinctions? How would we determine if either of these scenarios are plausible? What evidence should we be looking for, and at what point do we say, "Okay, the necessary evidence isn't there, so we need to propose some other mechanism"? Or is the evidence there?

I'm actually trying not to let this become a Creation-v-Evolution debate; I know that such would be totally out of line here. But I do want to see a discussion of how the Asteroid Impact theory could possibly have worked out to cause the mass extinctions--and more importantly, the mass non-extinctions at the same time--because the most popular (or at least, the most popularly published) scenario doesn't work for me.

The (hmm, my bag of pithy sayings is empty again) Curtmudgeon

The Curtmudgeon
2002-Jan-28, 10:46 PM
On 2002-01-26 22:37, James wrote:
I went to the Science Museum of Minnesota earlier today. They had and exhibit on the native cultures around the world. Anyway, I saw a map there from when National Geographic did their maps series some time ago, and it was a map of the continents as they moved over the globe over the history of the Earth. IIRC, the map they showed at the time of the K-T impact there was no Isthmus of Panama, but, look at where the asteroid impacted. It hit right on the inside edge of the(or what would become the) Yucatan Penninsula. You may have been right in that the tsunamis may have not gone to the Pacific, but I think that Donnie, lpetrich, and GrapesofWrath have covered the possibilities quite nicely. /phpBB/images/smiles/icon_smile.gif /phpBB/images/smiles/icon_biggrin.gif

Yes, the discussion is forming nicely along the lines that I was asking for: if we accept the impact, then how would that explain some phyla dying out almost immediately and others not at all? Many of the points raised still have problems explaining the selectivity, but that's always going to be the touchiest point and while I'd like to see it more directly addressed, my main concern is simply that it not be ignored as I feel that the photosynthehalt (if I may counterfeit a word) theory does.

My memory of similar maps to what you describe is that Panama was underwater only very much earlier (i.e., when North America broke off from Laurasia and South America from Gondwanaland, before they drifted into each other) or very much later (a break is postulated to explain certain of the anomalies of early Pleistocene life in South America, although it must have filled in later to allow the armadillos to get to Texas), but not during the dino age because very many of the South American dinos are essentially the same as North American, or at least closely-related. But that could be out-of-date info now, since I'm sure I haven't seen such a comparative display of maps in the last ten years or so. I do know there have been a lot more dino discoveries in Argentina, etc., since I saw maps done on it, so maybe they've found more distinct dinos.


You got a problem with Bell? May I ask why?

It's basically a long-standing personal joke among my family and friends. I hate telephones, and often simply ignore the thing when it rings at home if I don't feel like answering it, yet for the past twenty years I've been working in the telephony industry. So I've been threatening for years that my first priority with a time machine is to put an end to the Devil's Device by killing Bell before he invents it. (And yes, I'm fully aware that someone else would just invent it sooner or later, probably very close to the same time. As I say, it's really just a long-running joke, and given your mention of a time machine, it's my more-or-less instinctive first reply--it's not really intended to mean anything or to be taken seriously.)


Well, if you hadn't told me that you were, I probably would have had my suspicions, but I wouldn't have rejected your POV out-of-hand.

Unfortunately, many do. I don't mean many here on BABB--it's not a problem I've ever really seen here, but that could be at least in part because the posting rules don't allow for the types of discussions where it's more likely to happen. But I've never been ill-treated here on BABB because of being a 'thumper (of course, that also requires that I don't do any 'thumping on my part, beyond what I can justify as being astronomy-related, such as Star of Bethlehem discussions). But in more general discussion areas, and in the press, to raise questions vis-a-vis NeoDarwinism is often to get pummelled as a Creationist whether or not the label is true, or whether or not the point is justified by the form or content of the question(s) raised.



The ("K-Mart shoppers! We have a Blue Light Special on Dino-Whackers on aisle 9!") Curtmudgeon


LOL
That's a good one. /phpBB/images/smiles/icon_smile.gif

<Blush> One tries one's best.

The (okay, so how do I top it now?) Curtmudgeon

Russ
2002-Jan-28, 10:49 PM
On 2002-01-25 20:39, Donnie B. wrote:
One detail I've heard is that the Yucatan impact happened to hit an area where the rocks were rich in a specific substance (for the life of me I can't recall what it is;

It was Limestone. Calcium Carbonate. What was to become the Gulf of Mexico was full of corral reefs, which are mostly limestone.

The impact blasted Gazillions of tons of CO, CO2 and portland cement into the atmosphere. /phpBB/images/smiles/icon_razz.gif /phpBB/images/smiles/icon_lol.gif

lpetrich
2002-Jan-28, 11:00 PM
I don't object to someone being a Devil's Advocate, but one ought not to be a jerk about it; one ought not to whine about how wronged one is.

On the origin-of-life problem and the sea-saltiness problem, they are separate. Sea gains its salt from inflowing water, and loses its salt by reaction with newly-formed oceanic crust, deposition from evaporation of big shallow seas, etc. What's really necessary for the origin of life is lots of organic materials.

And one curious result is that the early Earth's atmosphere is now thought to be neutral, rather than reducing, as was expected from cosmochemical grounds. Urey-Miller experiments done with neutral experiments form very little organic material compared to those done with reducing atmospheres, which causes trouble. There are some alternative origin spots; instead of the oceans as a whole, hot springs would be a good origin site, because they often contain outgassed hydrogen gas, thus being a reducing environment, and because they have lots of opportunities for catalyzed chemistry along their surfaces.

As to moving away from Catastrophism, that was done because catastrophism has a rabbit-out-of-a-hat quality, and because of confusion of uniformity of natural law and uniformity of rate. Catastrophe theories have actually been revived in recent decades, and the Earth's surface is thought to have been significantly different in its early years. But these are now testable hypotheses; one can test whether a big meteorite struck the Earth by looking for iridium spikes and similar evidence, and one can study very old rocks for clues as to Earth's early days.

And just because we aren't around to see something does not mean that we cannot make hypotheses about it. And sometimes VERY strong hypotheses.

The Curtmudgeon
2002-Jan-28, 11:03 PM
On 2002-01-26 23:16, David Simmons wrote:
The disappearance of the dinosaurs would certainly affect the survival of every other species, but if they disappear, does it matter how?

I think it does. I think that any scientific explanation, whether it's the theory of how life evolved on this planet or the theory of how gas giants like Jupiter formed, has to take cognisance of all the repercussions of any mechanism invoked. In other words, if the most popular (or most popularised) theory of planet formation explained how Earth-like and gas giant planets could be formed in the same stellar system, but required that the gas giants were formed at much greater distances from the star than we see in our solar system, or required that visible asteroid belts appear between every planetary orbit, or the like, then I'd be raising the same objection to that. The How? is critical to a scientific theory, and when a theory is as widely accepted as being factual as is the case with evolution, then it's even more critical that it not leave any truck-sized holes open.

The ("It just did!" doesn't work for science) Curtmudgeon

The Curtmudgeon
2002-Jan-28, 11:09 PM
On 2002-01-28 09:55, ToSeek wrote:
What's to misunderstand? I just provided a link and echoed (somewhat tongue-in-cheek) the thrust of the article that asteroid impacts may not be as deadly as once thought.


Yes, let's not blame ToS; I was the one who started the whole interpretation thread, based on ToS' link. It may well be that I misunderstood the article, through skimming where I should have been reading. I probably took ToS' link statement, "Dust didn't do it", and read that back into the article when it really wasn't there in the original.

So let's just say that it's my own question about the Asteroid Impact, rather than the author of the linked article; the article sparked me into raising the point, even if it wasn't the point he was making.

The (I've been too busy to be focused lately) Curtmudgeon

The Curtmudgeon
2002-Jan-28, 11:42 PM
On 2002-01-28 18:00, lpetrich wrote:
I don't object to someone being a Devil's Advocate, but one ought not to be a jerk about it; one ought not to whine about how wronged one is.

Believe it or not, I'm really not trying to be a jerk. My sincere apologies if I'm coming across that way.

But I'm ignoring a good-sized chunk of the rest of your post, simply because I'm trying to be a good boy and keep to only astronomic topics here, and we're in danger of getting into that general evolutionary discussion I don't want to get into here. Your points are good, but you're answering my example posted above when I tried clearly to label that point as not being in the main flow of the Asteroid Impact discussion. I only brought it in as an example of the dichotomy I see in the biological/geological aspects of the theory, and not for it to be discussed on its own merits (or demerits).


But these are now testable hypotheses; one can test whether a big meteorite struck the Earth by looking for iridium spikes and similar evidence, and one can study very old rocks for clues as to Earth's early days.

Ah, but are iridium spikes necessarily evidence of asteroid/meteorite impacts? Or are there geological processes which could account for them? And are the iridium deposits as widely found as would be needed for the impact theory?


And just because we aren't around to see something does not mean that we cannot make hypotheses about it. And sometimes VERY strong hypotheses.

Granted, but we must always keep in mind that they are hypotheses, not facts. I have no problem with saying we have very strong evidence for the Chuxlub site being an impact crater; it's a very workable hypothesis and stronger than competing hypotheses. I do have a problem with just making a jump from that to the position that it was the Dino-Whacker, unless a workable mechanism for how it would have done so can be shown. (And I'm not stipulating that Chuxlub had to be the DW if one existed; I'm only using it because it is the generally accepted DW impact site. If you want to postulate a different DW impact site, that's fine by me and doesn't change my argument in the least.)

We know that something whacked the dinos; that much is a given fact (although "whacked" can be argued, if it is supposed to imply a short time period; I'm not using it that way here, only that the dinos were here and now aren't). I'm arguing that the Asteroid Impact theory has problems as the sole explanation for that.

The (and trying not to be a jerk about it) Curtmudgeon

GrapesOfWrath
2002-Jan-29, 04:07 AM
On 2002-01-28 18:09, The Curtmudgeon wrote:
Yes, let's not blame ToS; I was the one who started the whole interpretation thread, based on ToS' link. It may well be that I misunderstood the article, through skimming where I should have been reading. I probably took ToS' link statement, "Dust didn't do it", and read that back into the article when it really wasn't there in the original.
O, it was in the original. That is the title, no? Of course, you can probably blame that on an editor.

ToSeek
2002-Jan-29, 01:42 PM
On 2002-01-28 18:09, The Curtmudgeon wrote:

Yes, let's not blame ToS;


I heartily concur.

lpetrich
2002-Jan-29, 07:47 PM
As to why different sorts of planets formed in different places in the Solar System, that's reasonably well understood. Planets are leftovers from the solar nebula that were left behind as that nebula collapsed to form the Sun. These leftovers formed a big disk that orbited the Sun.

As the Sun settled down, it became hot enough to heat up the nearby nebula, driving off volatiles like water and ammonia and methane ices -- and hydrogen and helium. This is why the inner planets are mostly metal silicates (rocks) and iron-nickel.

The farther parts of the nebula did not get heated as much, so the ices condensed. And when sufficiently-large icy planets formed, they started accumulating hydrogen and helium, forming the Gas Giants. These planets then proceeded to repeat in miniature the formation of the Solar System; Jupiter's big moons repeat the procession from rocky to icy, though the other big planets have all-icy moons.

There was even some material that never completed the process of becoming part of a planet; the asteroid belt, the Kuiper Belt, and the Oort Cloud are big examples.

lpetrich
2002-Jan-29, 08:48 PM
As to why an iridium spike would be significant, that is an interesting bit of cosmochemistry. The average amounts of various elements in various places can be measured, and it turns out that the Earth's crust is short on iridium compared to the Earth's mantle or meteorites. This is most likely due to the chemical fractionation that has happened in continental crust as a result of volcanic activity. The continents are silicon-aluminum (sial) atop silicon-magnesium (sima), while the ocean crust is only sima.

So the Alvarez father-and-son team decided that iridium abundance would be a good way of measuring sedimentation rates; interplanetary dust can reasonably be assumed to arrive at a constant rate, and it would become diluted to a greater or lesser degree by Earth sediment, with more sediment meaning more dilution.

But the Alvarezes found a big spike in iridium abundance at the Cretaceous-Tertiary boundary -- too high and too short to be reasonably attributed to a change in sedimentation rate. So they considered the possibilities: volcanism and a meteorite strike.

There are two main kinds of volcanoes, which can be distinguished by their lava: sima volcanoes and sial volcanoes.

Sima volcanoes are spreading-zone volcanoes like at the Mid-Atlantic Ridge, and also hotspot volcanoes like the Hawaiian Islands volcanoes. These volcanoes produce lots of smoothly-flowing lava, but not a lot of dust; these volcanoes are relatively iridium-rich.

Sial volcanoes are found in island arcs and in volcanic arcs on continents; they are associated with subduction zones. They emit very viscous lava, and also dust/ash; these volcanoes are relatively iridium-poor. Mt. Pinatubo and Mt. St. Helens are good examples of this sort of volcano.

So the volcanoes that most easily put lots of dust into the atmosphere are the kind that release the least iridium.

Also, end-of-Cretaceous volcanic eruptions like the Deccan Traps had erupted over a few hundred thousand years -- and had produced the smoothly-flowing sima lava. Imagine a super-Hawaii in southern India.

So this leaves a meteorite. It would strike quickly, of course, and its dust would stay in the atmosphere for a few years, judging from the residence times of the dust from big volcanic eruptions like those of Krakatoa and Tambora.

Additional support for the meteorite hypothesis comes from the discovery of tektites, microtektites (glassy beads), and shocked quartz crystals with the right inferred age. The shocking of that quartz would be a natural result of the force of the impact (a few tens of km/s), and the tektites and microtektites would be metal-silicate rock melted by the impact and splattered outward.

So it's clear that there had been a big impact at K-T; finding an impact crater with the right age (Chicxulub) only clinches the case. What connection it had had to the K-T mass extinction is another question, of course.

David Simmons
2002-Jan-29, 09:05 PM
On 2002-01-28 18:03, The Curtmudgeon wrote:


On 2002-01-26 23:16, David Simmons wrote:
The disappearance of the dinosaurs would certainly affect the survival of every other species, but if they disappear, does it matter how?

I think it does. I think that any scientific explanation, whether it's the theory of how life evolved on this planet or the theory of how gas giants like Jupiter formed, has to take cognisance of all the repercussions of any mechanism invoked ...

In what way does the theory of evolution by means of natural selection "invoke" the mechanism of a catastrophic destruction of life?

I don't see how your example of a theory making an incorrect prediction about planet formation applies to this case. I don't remember the theory of evolution making any predictions about meteorite impacts or any other kind of global catastrophe.