|In a message dated 5/29/2002 8:49:32 PM Eastern Daylight Time, firstname.lastname@example.org writes:
you still need to realize that all that vaporized earth is going to be put into orbit, regardless of what your shockwave is doing
Oh, I assure you..... I do realize that rock has been vaporized and pitched up into the atmosphere.... And that's just it you see..... Large quantities of rock was vaporized..... Vapor.... This stuff gives you some types of your acid rains and etc, depending on the rock compositions... high sulfur content, etc. I'm sure you know that the rock you are talking about is that which was basically crushed to a fine powder and launched up into the stratosphere... The impact explosion caused by an object some 10 km in diameter would have ejected some 21,000 cubic km of debris out of the forming crater..... Around 1,700 cubic km of this debris would have been launched up into space at some 50 times or so the speed of sound..... Or so we think. Shot into earth circling trajectories, the debris would have remained in orbit for only a tiny period of time.... minutes maybe..... before slamming back into the atmosphere. Some would have hit the ground, others would have been completely! v! ! aporized. Those pieces that are not completely vaporized reach the surface from space as tektites. Most are only centimeters in size, while others can weigh in excess of several kilos. Microspherules are tiny, glassy, rapidly cooled molten rock droplets that supposedly ignited wild fires around the world and set the atmosphere to broiling temperatures as they radiated their heat. They apparently originate from the condensing vapor of the melt sheet. The stratospheric debris would stick around for varying amounts of time, depending on the size of the particulates. Upper level winds, heat from the sun, etc, would shuffle it around, making it thicker in some places, lighter in others, and maybe even non-existant on other parts of the globe.
Rob, the point you are talking about is one that I briefly touched on concerning the "nuclear winter" hypothesis. It apparently wasn't as bad as was once thought...... As with anything that deal with these mass extinctions, we don't know this for sure..... It's just a maybe :-) ..... The debris tossed into the atmosphere was nothing compared to the soot, ash, and smoke bellowed into the atmosphere by the fires supposedly started by the infalling debris. That was the main culprit when it came to darkness..... That is if it even turned completely dark.........
The question is one of did the impact actually produce as much dust as we say it should have??? As the Science article "No 'Darkness at Noon' to Do in the Dinosaurs" states, perhaps the "darkness at noon" dust scenario was more like a dim winter's day in Seattle. It's all about estimating the amount of the smallest bits of debris from the impact. To cut off photosynthesis and starve the dinosaurs, unbelievable amounts of submicrometer particles would have to have been tossed onto the atmosphere where it would have floated for a few months before being blown out and washed out. The problem is that this fine dust cannot be measured directly in the 3-millimeter-thick global layer of impact debris. It would have weathered away to clay. Geologist Kevin Pope of Geo Eco Arc Research in Aquasco, Maryland, searched the literature for reports of the size and abundance of larger, more rugged bits of impact debris.... your typical quartz grains averaging 50 micrometers in siz! e.! ! What was found is that the global layer consists mostly of relatively large spherules condensed from the plume of vapor that rose out of the crater from the impact. From these measurements, an understanding of the dispersal of the dust cloud was attempted. What Pope found is that the size of this larger debris dropped off sharply with increasing distance from the impact.... Something like dust falling from wind-blown debris clouds rather than debris coming from a blast that sent it around the globe. When Pope modeled debris dispersal by winds alone, his modeled drop-off in both size and mass of debris grains.... It resembled what was seen in the actual preserved global layer. These results remained true only if the total amount of debris produced by the impact was relatively small. Assuming that the impact debris had a distribution of particle sizes similar to that of volcanic ash, the conclusion is that less than 1% of the debris consisted of submicrometer particles. This ! me! ! ans that the dust in the global layer was 2 to 3 orders of magnitude less than what would be needed to shut down photosynthesis.
Of course this is a very complicated problem. What's going on here is basically all inferences in the relation between large and small particles..... and it's not very obvious. Those that disagree with Pope's assessment say that a 10km impactor should have generated copious amounts of dust..... But as I sated in my post, some admit that "if dust really can trigger major extinctions, there should have been many impact-triggered extinctions in the past few hundred million years, because there have been many impactors larger than the few-kilometer minimum for a global dust cloud". But, since none besides the one at the KT has been "proven", some researchers are leaning toward global fires and their sun-blocking smoke as the main villain in the death of plant-life and the shutting down of photosynthesis. And as I said, these types of fires would come from the vapor that condensed into blazing-hot droplets, or microspherules, that fell to the surface, radiating ! he! ! at on the way down. Impactors in the range of 10km and larger are the only ones that could possibly throw up enough vapor to set the entire planet on fire. But again..... as I said in my post...... even this doesn't agree with the known fossil record and every single one of its recognized extinction events.
Simply put, if dust really isn't to blame for the mass extinctions, then the environmental punch from large impacts would be less than researchers have generally assumed.
Speculating.... I'm betting that impactor trajectory is a big factor concerning how much dust is actually tossed into the atmosphere. Those that slam into the earth, forming bowl craters, deposit all their kinetic energy directly into the earth. The massive amount of resulting debris is thus blown out of the forming crater and into the atmosphere. Impactors with oblique trajectories, like that of Chicxulub, deposit most of their kinetic energy, not into the earth, but directly into the atmosphere itself. Thus, less amounts of debris is blown far out of the crater and up high into the atmosphere. This could also explain why the melt sheet, according to studies like that of Horner's, apparently didn't reach Montana..... It simply wasn't as large as assumed since it simply wasn't made up of massive amounts of material... Or, being as "light" as it would have been, that is, having less material,..... and traveling at such faster then sound speeds, the melt sheet might have h! ad! ! an angle to it that caused it to race along the ground for only a few hundreds (thousands???) of km before it arched upward into the atmosphere... Topography of the ground itself could be a factor. As it did so, it dropped its cooling, and thus much denser microspherules, in the pattern observed by Pope. It's like taking a broom and sweeping a thick layer of dust. The dust cloud moves along the surface for a bit but then lifts up off the ground, arching up as it drops its larger clumps. (Forget the effects of static electricity for a minute..... even though this would have been a factor in impact dust as well.) This says nothing to the fact that the KT impactor hit ocean first..... not rock. Plasma, vapor, ... all that fun.... I don't know what these variables would have done. But, since I do not own a super computer, nor a projectile accelerating gun with super slow-motion photography equipment, I can't test my ideas.
Everyone has the mechanism they like the best..... Since we don't know the facts, pretty much anything is up for grabs.