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Dinosaurs, Mammals and survival at the KT boundary

 
 
farmerman
 
  1  
Reply Thu 2 Nov, 2006 11:55 pm
talk--If all things are equal, there wasan equal chance for fossils to form all the way through the MAastrichtian. Fossils form very well in desert conditions, (dessication plus added wind blown sediment. The fact that the dinosaurs were disapearing was not an artifact of preservation anomalies, it was because there were no more of a particular species. We have a Creationist on the line who makes the same argument . Paleosols of te late Cretaceous were often carbonates, hence the name of the Cretaceous as the time of the "chalk" seas would mean that the sea giant reptiles of the Parapsid and uerapsid sub classes would be preserved in the ocean sediments and they just disappeared by mid to early late cretaceaous.

Extinctions leading up to a major time break that we automatically define by extinction is circular reasoning after all. SO Im not saying that a comet wasnt a factor. Most geologists now just dont believe that it was the single factor for the loss of dinosaurs, 5 orders of mammals, certain mollusca and many sea creatures. There has to be another longer term causative factor in this , the third(actually tied for second) place extinction.
There was another minor extinction that occured in the Miocene(15 MYa) and that one is tied to a bolide hitting the Chesapeake BAy. A detailed (special investigation) account is being prepared by the USGS and a book about it was written by a geo named Wiley Poag. From this bolide hit, and from the extensive reaction measured in the pre Miocene sediments, we now have developed newer lithotectonic models that predict the response from the crust ,M discontinuity, and down to the asthenosphere where Shear waves and compression waves are attenuated . The upper mantle and lithosphere are modeled more like yogurt and not a sheet of metal. Thats why geologists in the 50's were at a loss to explain why crustal material was so deformable but seemed to need high shear strengths to transmit energy of deformation for 100's of kilometers. Now we know that ist because srust "rides" over deformable "putty" that moves like the plumes of a lava lamp. Plastic deformation occurs in most all rock bodies no matter how indurated they appear. So a bolide crater like Chixclub would have presented itself in a fashion that we can now fairly accurately predict. The silicate rocks coisite and stishovite occur at extreme distances from the crater area and can be better used to show the actual "fabric" of the bolide hit. The low Angle projection for the bolide at Chixclub isnt defined by the shape of the subsurface crater because that feature is buried under the mobile crust of a moving plate. Instead, the shape of the stishovite shock area is sortof like a ellipse with an open bottom which is similar to the feature at Tunguska, except Tungska is more "bow tie' shaped since its felt that this was an air burst. The pattern of shocked quartz(stishovite/coesite) is important for minerals exploration.


I sometimes do exploration work in cratered areas because I explore for claims for Titanium minerals and rutile is another consequence of bolide smacks. (everything readjusts its crystal shapes and turns into tetrahedrons and that yields rutile(anatase) an Fe/ Ti ore that is easy to work ). Bolides are really good mineral locations because the shocking imparts an unstable "crystal lattice change" on most of the minerals and these extend out quite a distance. Since we can tell stishovite by gravity separation in placer sands, we can track bolide hits very easily just by specific gravity without any fancy equipment so these bubbas are easy to find after we see examples of hit areas on areial photos.
While this has nothing to do with dinosaurs it lets you know that many tools we use in paleo analyses are open to analyses from a myriad of directions and geophysics, computer modelling, old fashioned prospecting, as well as drilling have all come at the chixclub from a number of different directions and left many of us quite skeptical of the "terminator theory"
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talk72000
 
  1  
Reply Fri 3 Nov, 2006 12:54 am
farmerman, thanks for all the info. I am not saying the asteroid was the main factor of extinction. I am just describing the destructiveness of the asteroid impact. Paleontology is a sketchy science at best. It is tough trying to figure out what actually happened millions of years ago as the evidence all disappeared thru erosion, corrosion, weathering, whatever. I would think it is more a hodge podge of snapshots than a video.
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farmerman
 
  1  
Reply Fri 3 Nov, 2006 06:31 am
That a precise analogy talk. I had a colleague give a talk regarding the use of tree rings in determining the rain cycles of certain areas in the ancient west. He said its like a " collection of family pictures that have been torn up and thrown about for a 100 mile radius. WE have to piece the p[ictures together and then try to find their order"
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talk72000
 
  1  
Reply Fri 3 Nov, 2006 08:41 pm
stuh505, thanks but why the explosion? Is it because kinetic energy is converted to pressure with high speed meteor stopped by stationary earth? I guess also the superhot meteor would expand the trapped air and explode?
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stuh505
 
  1  
Reply Fri 3 Nov, 2006 11:16 pm
Because the speed of an impacting meteorite is over 10 kilometers per second, and the energy delivered is proportional to the square of the speed. At this speed and mass, the energy delivered is so great that the meteorite is completely vaporized on impact. Thus it is basically the same as a point explosion on the surface, and the metoerite material is just dispersed into the atmosphere. If the meteorite comes in at an angle that is nearly tanget, like 80 degrees, then it does break up creates a linear chain of explosion patterns.
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talk72000
 
  1  
Reply Fri 3 Nov, 2006 11:49 pm
But the case in point is a 12-mile diameter asteroid and an 18-mile cum 3-mile thick crust at the Yucatan Peninsula. The atmosphere is only 30 miles and the crust 18 miles so the combined resistance is 48 miles which is 4 times the the width of the asteroid which would pass thru in less than a second hardly enough time to burn up. The composition of the asteroid is what would determine the scenario. If it is one solid piece of rock it would certainly pierce the crust with hardly any damage. I doubt an 18-mile crust would vaporize a 12-mile asteroid. If the asteroid was a defunct comet then it is a loose conglomeration of rocks and dirt with ice. After all, a 12-mile diameter object would have a very small gravitational pull to solidify the mass of a comet. This could probably burn off the fluffy stuff in the atmosphere with the hard core of rocks penetrating the crust and partially exploding on impact and spraying the earth with a world-wide fall-out of iridium.
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stuh505
 
  1  
Reply Sat 4 Nov, 2006 12:36 am
Meteors are objects that burn up in the atmosphere. Meteorites are objects that do not burn up in the atmosphere. Therefore, meteors are just the low density comets which are composed of dust gas and volatiles. They make a neat show but are of no danger.

We are talking about a meteor. The meteors do not burn up precisely because they are dense. And they are dense because they form in a completely different way. Some of them are from exploded planets or proto planets but most of them are basically just asteroids.

As such the meteor did not rely on its own self gravity to form and you cant use that as a measure of its density. There are a number of different types of meteors...they can be classified based on their type mainly: stony, iron, or stony-iron...or based on their source, being primitive (From an undifferentiated body) or from a differentiated one.

Most of them meteors are primitive stony meteors with compositions similar to materials found on Earth. The KT meteor was presumed to be a stony meteor. They have density around 3 g/cm^3...much less than the density of the pure iron differentiated meteors.

When a stony or iron meteor enters the atmosphere, of course it does not burn up. The outer layer is heated to incandescence but the heating only penetrates a few centimeters and this has cooled off completely by the time it strikes the ground.

We are not talking about a solid iron meteorite...that would basically be the result of the core of a small planet being extracted and hurled at Earth. Not likely!

I cannot give you the exact mathematical equations but the experts in this field agree that meteors of this size do vaporize and create an explosion. It is not just the meteor's own material that is thrown up. A lot of matter from the planet can be thrown up, too.

I dont know exactly how much, or if the crust was ruptured or not, ...but I do know that it did not "penetrate" the crust as you describe. It certainly is possible to rupture the crust, as I'm sure happened when the meteor that formed the moon hit Earth.
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talk72000
 
  1  
Reply Sat 4 Nov, 2006 01:03 am
With a velocity of 100,000 mph and a meteor almost as wide as the crust is thick, I am not at all persuaded with the vaporizing explanation. The crust has already given way in the form of the crater and being so close to water the crust is nearly 3 miles thick or slightly more. The meteor got swallowed up by the molten mantle underneath the crust. Of course, earlier I mentioned that at impact loading (high-speed) all materials behave like solids so the mantle even though molten would behave like a solid and thus smashing the meteor to pieces on impact and exploding under the crust.
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rosborne979
 
  1  
Reply Mon 30 Jun, 2008 05:03 pm
We got off track on impacts and such, but I still don't think we've answered the original question...

The original point of this thread is that at the time of the KT extinction, there seems to have been relatively little difference between the classic survivors (mammals), and dinosaurs that went extinct.

In order to help the thread along, at this point I would like to narrow the question from "Dinosauria" in general, to specifically Therapoda.

In other words...

Some Therapods were warm blooded, Mammals were warm blooded.
Some Therapods were small, Some Mammals were small.
Some Therapods had feathers (down), Mammals had fur (fluff).
Some Therapods ate eggs, Some Mammals ate eggs.
Therapods were robust and diversified, Mammals were robust and diversified.

The differences between the two groups are not dramatic, and yet the result was.

Many creatures from the mammalian line survived, but from the Therapod line, only birds survived. I can perhaps understand why birds survived, because of their unique skills (flight). But that really leaves us with the original question: Why did multiple lines of Therapod vanish, when multiple lines of mammalians, all very similar in characteristics survive?
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farmerman
 
  1  
Reply Mon 30 Jun, 2008 06:03 pm
Boy, If you guys dontquit arguin Im goin home.
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spendius
 
  1  
Reply Mon 30 Jun, 2008 06:07 pm
Chicken!
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rosborne979
 
  1  
Reply Mon 30 Jun, 2008 06:32 pm
farmerman wrote:
Boy, If you guys dontquit arguin Im goin home.

I'm not arguing. I would just like to explore the event and the resultant evolution in more detail. That's all.
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spendius
 
  0  
Reply Fri 4 Jul, 2008 06:51 pm
I need one more for a Ten-Up on the Science Forum so Hiya Ros how's it going?
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spendius
 
  1  
Reply Fri 4 Jul, 2008 06:53 pm
That's serious trolling eh ros?
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rosborne979
 
  1  
Reply Thu 6 Feb, 2014 03:26 pm
Only slightly related, but couldn't find a better thread for it: http://www.reuters.com/article/2014/02/05/us-science-arctic-idUSBREA1425W20140205
Setanta
 
  1  
Reply Thu 6 Feb, 2014 03:41 pm
@rosborne979,
Thanks Roswell--i am bemused because paleontologists have long stated with confidence exactly what the diet of periglacial species was, and they didn't mention wildflowers. It's always interesting to see new data crop up in these matters.
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farmerman
 
  1  
Reply Thu 6 Feb, 2014 10:05 pm
@rosborne979,
you know what they say about extraordinary claims?

There were also the same number of derived species of non arctic versions of these animals that lived in the arboreal and subtropics that also became extinct.
We have forested swamps in upper Pa and lower NYS that became ice free forested areas with aspens , willows, swamp maples etc and the megafauna that hung in there were also become extinct.

There was another "Bolide of the Holocene Bottom " hypothesis, but nobody's found it yet.
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farmerman
 
  1  
Reply Sat 8 Feb, 2014 07:06 am
@rosborne979,
If we look at habits of such megafaunas as brown bear and grizzly bear, we see that a seasonal protion of their diets are flowers and , often, linden buds. I think that omnivorous animals and herbivores adapt to whatever is available.
This guy seems to be saying that flowers were a larger part of the diets. I gotta reread it carefully to see what he said about pollen cores
rosborne979
 
  1  
Reply Sat 8 Feb, 2014 11:57 am
@farmerman,
If they are right, that environment must have been spectacular with huge prairies of blooming wildflowers.
panzade
 
  1  
Reply Sat 8 Feb, 2014 12:21 pm
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