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grandpa

So, this is as good a time and place as any to ask a question that has bothered me from the first time I heard about the

Chicxulub impact

mass extinction theory.  Keep in mind, I live in Austin and need only travel a 100 miles or so to visit a noted K/T boundary exposure with a high indium content layer along the Brazos River. I'm also not so far from the Yucatan Penn.  So here's what I can't figure out.

 

This major catastrophic event occurs - a large asteroid hits the earth.  Immediately there is a massive explosion that wipes out all life for many, many, many miles, poisons the earth's oceans and leads to a "nuclear winter" type event that kills the majority of animal and plant life (both predator and prey) on earth and in the sea.  Many animals and plants die immediately from the impact, more die very soon, others exist for (how long - 1000 yrs, 10,000, 100,000 more?) as life continues to decline from the event, species die out, domino effect leads to others of the food chain dying, etc., etc.  (How thin must 1000 , 10,000, 100,00 yrs of sedimentary deposits  be?)

 

With that as a given, shouldn't there be a thin layer of sediment just littered with fossil evidence covered with debris and further sedments from the impact.  I'd think that the K/T boundary, along with a layer of high indium content and such things as bedoites (impact glass metamorphs also found about 100 miles away) would also have a layer just inundated with fossil life that died immediately or soon after (say within 100 years) impact.  Where's that layer?  What's up with that?  Why was there not an immediate affect on life, or if there was, where is the fossil evidence of that?  I would think there would be a global layer indicative of such a pin-point-event mass extinction. 

 

If the

Chicxulub impact acidified the ocean instantly wouldn't we for sure find a thick layer of ammonites, etc. all laying there to be picked up that represented the entire order that existed at the end of the Cretaceous, not all in one place mind you, but all in one thin layer globally, all having died at virtually the same time.

 

The lack of such a layer (or is there evidence of one?) leaves me thinking more may have been involved,( e.g. major volcanic activity set off by the impact that lasted a "long" time (X-1000 -  X-Million yrs.) and slowly made the environment incompatible.  Now I don't have the science to back that up, I'm just hypothesizing because I don't see the evidence to back up what I think an impact mass extinction theory would offer in the fossil record.

 

Please help me understand what I am missing and explain why the asteroid extinction makes sense vis-a-vis the fossil record.  (Also, please point me to the high-density fossil layer that supports the Chicxulub theory - I want to collect THERE!)

 

I'm looking at it from a lay-person perspective and need more understanding.  I have no problem with the "theory" if the facts "on the ground" can be offered to validate it.

 

Grandpa

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DPS Ammonite

@grandpa In response to Grandpa’s great question, I would think that there might be an increase or at least a difference in preservation of fossils found in the sediments just above the boundary. Other than a recent article about a possible site in North Dakota that claims to be a very rich site, https://www.sciencedaily.com/releases/2019/03/190329144223.htm,

I could not quickly find any other articles about mass KT boundary fossil sites that are rich in fossils.

 

I have some unsupported ideas as to why rich KT sites are rare. 

 

On the land, creature preservation is rare. It take a catastrophic event to bury creatures such as a flood, landslide or volcanic eruption. If the bolide caused a fire, little would be left to fossilize except for a little fine organic matter. If a giant wave swept everything away, the creatures might have been ground down into pieces too small to ID. A little layer of impact related glass spheres now turned to clay would not have been enough to bury most creatures.

 

If the bolide did increase the acidity of the ocean and probably rain too, the acid may have dissolved the creatures away before they could fossilize in both ocean and land sediments.

 

Also, if the creatures died out over a period of hundreds or thousands of years, a large spike in fossil creation might not occur and be noticeable in the geological record.

 

Further research is needed to find more KT sites with fossils.

 

 

 

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Scylla

I wasn't there, but imagine 1000's of carcasses piled up somewhere on the charred and battered surface. They would rot away in a relatively short time period unless burried, frozen, or mummified. The latter two categories would then rot when thawed or rehydrated. I think a similar thing is happening now with all the mammoths in Siberia rotting as the permafrost thaws. So where would carcasses pile up and then get burried? Maybe at the base of mountains or canyons? But the canyons will erode. So most of the earth's surface would not be amenable to these fossils forming in the first place. Even if they formed, they may have eroded away, or are just burried too deeply for us to recognise them. I do expect some sites should have fossil evidence of such a global catastrophe, and maybe the Tannis site is just that. I also think marine deposits would be more likely than terrestrial ones.

 

https://www.newyorker.com/magazine/2019/04/08/the-day-the-dinosaurs-died

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grandpa

@DPS Ammonite thanks for the thoughtful response.  While I find these interesting hypotheses all; I, however, find myself unconvinced sufficiently by any or all of them together.  It would seem that each of the events you posture would leave their own footprint in the sediment layers.  Am  I wrong?  Also, if I can find an iridium-rich layer (not indium) still present and bedoites (impact glass) still laying around outside Bedo, Tx , why is there not at least a layer of ash or fossilized "surface" disturbance as evidence.

 

No, I think this deserves more thought, at least on my part, before my questions are answered.

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grandpa

@Scylla thanks for your thoughts as well.  Still, I think about the ashfall area in Nebraska.  I would think, if volcanic ash covers up that many fauna and beautifully preserves them - predator and prey alike  side by side on a  lakeside - an asteroid striking the earth and the ash from the fires and dust from the explosion which would fill the atmosphere in massive (I can't even imagine) amounts and then rain down back on the earth's surface would, somewhere at some distance from the event on the planet, lead to much fossil evidence of such a massive, planet wide impactful event.  Wouldn't you?

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grandpa
56 minutes ago, DPS Ammonite said:

Other than a recent article about a possible site in North Dakota that claims to be a very rich site, https://www.sciencedaily.com/releases/2019/03/190329144223.htm,

@DPS Ammonite this is much more along the lines of what I'm thinking of.  Yes, there should be more sites, many more like this if the theory is correct.

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Randyw

That is an excellent question @grandpa. My own personal thought unsupported by any evidence is that the dinosaurs were already pretty much extinct before the impact. Quite a bit before the impact there is a smaller biodiversity of dinosaurs and actually very few dinosaur fossils found Within a couple of meters of the boundary layer.  So I suspect that the dinosaurs were on the way out or even completely gone except for a few isolated pockets before the impact.

While there has been a few isolated single bones found as young as 61 mya they are still highly controversial and the testing methods were themself untested.

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grandpa

@Randyw you raise an interesting point, and one that I've just been reading about this evening/morning as I try to better educate myself on the K/T extinction event.  I was just reading about the Deegan Trap in Cretaceous India and the improved dating of the 3 major periods of volcanic activity associated with that area.  The article points to the second, and strongest period of volcanism as beginning some 250,000 years prior to the Chicxulub impact and extending right up to the K/T boundary.  The authors argue that this event resulted in the decline of the dinos and Chicxulub was the final kick that pushed the dinos over the edge.  A "decline to a slow end" scenario seems to better align with what little I understand about the fossil record of that boundary period than a "flourishing biota with a punctuated end" and no bodies to show for it.

 

One thing my evening's reading has opened my eyes to is that there is still a lot of controversy about what all was involved in the extinction - many ideas, little all-convincing evidence.  So I guess the extinction scientists have some job security for the near future at least.

 

Now we need to get to work on the 6th mass extinction and see if we can escape it somehow.

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Scylla

Not all ash is the same. Most volcanic ash is mostly silicate, great stuff for preserving dead animals as fossils, especially a thick layer of it. Most ash from fires are metal carbonates and very alkaline, great for making soap from animal fats. Even if dinosaurs were gone before the impact, something should have been around to get killed and fossilized.:zzzzscratchchin:

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Randyw
1 hour ago, Scylla said:

something should have been around to get killed and fossilized.:zzzzscratchchin:

Yes. But what if the impact while major wasn’t the disaster invisioned. IE what if many of the creatures alive then survived the impact but the environment effects are what caused the biodiversity explosion that occurred afterwards. There are theory’s that believe that great environmental stresses speed up the evolution of species as “Mother Nature” tries out new models to cope with said stresses. Just speaking hypothetically of course.

theres a whole stretch of time where there were no large animals and we all know how few small mammals and stuff get fossilized..

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Randyw

After all. How may huge impacts have there been but with no huge fossil beds around them? Not talking worldwide in these cases but as local.

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