What Really Did Kill The Dinosaurs?

Mythopoeika

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"The changed environmental conditions meant the bigger animals (dinos) died out before the smaller ones (mammals)"

But even the tiniest (chicken sized) dinosaurs disappeared, whereas the larger (badger sized) mammals survived.

Still a lot of mystery surrounding the extinction event.
Global cooling. Small dinosaurs couldn't withstand the cold. They weren't able to make their own heat like the big dinos.
Mammals were able to survive, being warm-blooded.
 

Xanatic*

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Why did turtles and crocodiles survive then?

Oldrover is referring to birds. Birds are not dinosaurs, they are a spin-off.
 

rynner2

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"The changed environmental conditions meant the bigger animals (dinos) died out before the smaller ones (mammals)"

But even the tiniest (chicken sized) dinosaurs disappeared, whereas the larger (badger sized) mammals survived.
Evidence please. 'Had larger (badger sized) mammals' even evolved at that early date? The general thinking (as I understand it) is that the original mammals were tiny, shrew sized creatures, too small to make a decent mouthful for even a small dino. Only when free of predation by various dinosaur species were they free to evolve into different (and larger) sizes.
 

rynner2

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Why did turtles and crocodiles survive then?
Aquatic reptiles would have avoided many of the problems of the asteroid strike aftermaths.

But I'm sticking with the University professors and other technical experts, rather than worrying about some people (qualifications unspecified) who choose to post on an internet message board! :twisted:
 

EnolaGaia

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Why did turtles and crocodiles survive then? ...

The usual explanation is that they were aquatic, and their food chain wasn't disrupted to the same extent as it was on land.
 

EnolaGaia

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Evidence please. 'Had larger (badger sized) mammals' even evolved at that early date? The general thinking (as I understand it) is that the original mammals were tiny, shrew sized creatures, too small to make a decent mouthful for even a small dino. Only when free of predation by various dinosaur species were they free to evolve into different (and larger) sizes.

The semi-aquatic proto-mammal* Castorocauda (discovered in 2004) was circa 17 inches long (nose-tip to end of its beaver-like tail) and weighed an estimated 1 - 2 pounds. It lived circa 100 million years before the K-T boundary event, earning it the title of oldest known animal with hair / fur (for the time being).

* I say 'proto-mammal' because there's a longstanding dispute over where to draw the line between ancestral forms and 'proper mammals'. A liberal interpretation (based on features) opens the door to including Castorocauda. A stricter interpretation (the so-called 'crown mammal' approach, limiting 'mammal' attribution to only those lineages leading to today's mammals) would exclude it.

All the current mammal taxonomic orders pre-date the K-T event. Under current categorizations, they represent the descendants of all 10 (out of 15) orders that survived the K-T boundary.

Other examples refuting the notion of all mammals being tiny terrestrial shrew-like beasties as of the K-T event are cited on the Wikipedia page for Castorocauda:

https://en.wikipedia.org/wiki/Castorocauda
 

PeteByrdie

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Still more than twice the number of dinosaur species on the planet than mammals. The question of what killed the dinosaurs is pretty outdated. It's a shame the BBC isn't more up to speed.
I haven't yet had the chance to view the documentary, but my experience of science reporting is that they feed us simplified information, with only those lines of enquiry that aid the narrative of scientific discovery they intend to portray. I think there's still a mystery why so varied a group as non-avian dinosaurs vanished, perhaps especially because some bird species survived. Factors sometimes ignored, however, include the paucity of the fossil record, which doubtless gives an incomplete picture of the rate of extinction, and that a great many species didn't survive the event, non-avian dinosaurs were not selected specifically for extinction.

Oldrover is referring to birds. Birds are not dinosaurs, they are a spin-off.
Taxonomically, birds are theropod dinosaurs. There's nothing wrong or especially misleading in describing them as such.
 

PeteByrdie

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But I'm sticking with the University professors and other technical experts, rather than worrying about some people (qualifications unspecified) who choose to post on an internet message board! :twisted:

Ha! Nothing wrong with that. But we can speculate. After all, as forteans we know the history of science is also a history of some ideas becoming dogmatic, for a while at least.
 

oldrover

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But I'm sticking with the University professors and other technical experts, :twisted:

Me too, that's why I find the type of coverage on the BBC sloppy at times. It's not as if they've got a particularly good record in the last few decades accuracy wise when it comes to dealing with ancient life.

Not sure what you mean by this. The changed environmental conditions meant the bigger animals (dinos) died out before the smaller ones (mammals), which could still scrabble some sort of small-scale living.

Can you explain why the BBC (and its army of experts, universities, and researchers) should be 'more up to speed'?

I don't say through some sort of bizarre taxonomic correctness, but I think that to continue to talk about 'The Day the Dinosaurs Died' is lazy and misleading. Think of it this way, as I said there are twice as many dinosaur species today than mammal, by species just under half of the mammals are still vulnerable to predation by dinosaurs, and by individual the vast majority are. Dinosaurs don't often occupy the larger body niches today, the exception being the ratites and only a few hundred years ago this was even more pronounced with the moa and the aepyornis. Go back further and you have in places apex predator roles being filled by large ground birds throughout most of the Cenozoic, and that's in the presence of large predatory mammals. And today in some areas the role of top predator is still filled by dinosaurs. Aside from that they dominate many ecosystems the World over, occupy every continent, and have radiated to fill pretty much every niche you care to name in one place or another.

Of course all this is only relevant if you believe birds are dinosaurs, and frankly that's not a conversation anyone should be having today. As Pete says above birds are Therapod dinosaurs. Rather than the idea some might have that they appeared only at the end of the Cretaceous, their history goes back into the Jurassic and they're not even that derived either, as many/all of their features are shared with other Therapod lineages. And there's plenty to be said about just how diffuse a line there is between the birds and some of the most famous non availan dinosaurs, velociraptor, gigantoraptor, etc. But that's one I do recommend you look to the experts for, but pick them carefully, go for a scientist regularly publishing in the field.

So, I think to talk about dinosaur extinction is something an institution like the BBC, part of who's remit is to educate, should avoid. Instead, they should be reflecting and underlining current research, and addressing the current more complex and interesting questions about ancient life.

And yes, there were badger sized mammals in the Cretaceous, and they probably ate dinosaurs. Edit: Here's a snippet from 'Nature', with evidence that they did prey on dinosaurs. https://www.nature.com/nature/journal/v433/n7022/full/nature03102.html
 
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oldrover

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Global cooling. Small dinosaurs couldn't withstand the cold. They weren't able to make their own heat like the big dinos.
Mammals were able to survive, being warm-blooded.

Don't fall into the trap of thinking dinosaurs were cold blooded, or that mammals were warm blooded. The terms warm and cold blooded are these days largely binned, internal temperature regulation is a spectrum, present in some species absent in others. For example not all mammals alive today let alone the Mesozoic are ''warm' blooded. Not even all Eutherian mammals are. And definitely not all reptiles are 'cold blooded'.

Internal temperature regulation in terrestrial animals may be an adaptation toward parental care, I think it is. And it's interesting to see that in the Monotremes it's absent until breeding takes place, at which point and during the nurturing phase they start to metabolise heat. Also there's a species of python which shivers while brooding to increase its body temperature in the same way that heterothermic mammals do. Most interesting to me is the question of whether the Crocodilians are derived ectotherms, and if so whether their decision to leave the kids to it is part of that.
 
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oldrover

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To expand a little on the 'Nature' link on Repenomamus giganticus, the dinosaur munching Mesozoic mammal (Enolagia's point about the use of the term noted)

When the dinosaurs ruled the world, the mammals hid in the shadows, daring to grow no bigger than shrew-like insectivores that hunted at night. Or so we thought.

https://www.newscientist.com/article/dn6874-large-mammals-once-dined-on-dinosaurs/

Turns out the size in this source is equated to a honey badger.

It lived circa 100 million years before the K-T boundary event, earning it the title of oldest known animal with hair / fur (for the time being).

The earliest known evidence for hair is from the Permian, but it's not not associated with any particular animal as it's known from coprolite. Which is an issue because that's before the remains of the earliest known candidate for hair, as inferred by facial nerve channels. https://www.nature.com/articles/srep25604

* I say 'proto-mammal' because there's a longstanding dispute over where to draw the line between ancestral forms and 'proper mammals'. A liberal interpretation (based on features) opens the door to including Castorocauda. A stricter interpretation (the so-called 'crown mammal' approach, limiting 'mammal' attribution to only those lineages leading to today's mammals) would exclude it.

All the current mammal taxonomic orders pre-date the K-T event. Under current categorizations, they represent the descendants of all 10 (out of 15) orders that survived the K-T boundary.

Taxonomy is an ever shifting thing isn't it. I do like Crown group definitions though. Personally, as a layman I struggle to decide where the term 'mammal' should be applied, or reptile for that matter, in terms of the early representatives of the two groups. After the Amniotes were we all reptiles back then? Or is there a case for applying another term for us Synapsids at that stage?
 

EnolaGaia

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... The earliest known evidence for hair is from the Permian, but it's not not associated with any particular animal as it's known from coprolite. Which is an issue because that's before the remains of the earliest known candidate for hair, as inferred by facial nerve channels. https://www.nature.com/articles/srep25604

Yes, agreed ... In my earlier post I deliberately limited my retrospective scope to 'specific known / named animals exhibiting key mammal-like features' (in the context of responding to rynner2's query). You're right - certain key features associated with 'mammals' (and 'mammals alone' in the popular mind ... ) can be traced much farther back than most people realize.

All of which comes back to ...


Taxonomy is an ever shifting thing isn't it. ...

Indeed it is, and that makes it difficult to know what's what when the basic scheme keeps shifting beneath you.

Taxonomy is a double-edged sword. On the one hand, it's a great aid for sorting and making sense of things. On the other hand, premature commitments to categorization can problematically bias subsequent interpretation / incorporation of new data. With respect to evolution (or similar ongoing processes) it can only ID the waypoints, and it offers little value in understanding the course of events that comprise the 'real story'.

Unfortunately, we can interrogate the past only through its surviving evidence, leaving us with a set of found items whose interrelationships we can only imagine. It's like seeing a movie only in terms of widely-separated little glimpses. You can lay out the cast of characters spied within those glimpses, but you can never be sure what happened to or among them along the way. Even worse - you can't be sure you've even seen all the characters!

In the mean time, the general population tends to think of evolution in simplistic terms - e.g., a fairly linear path condensed into a fast-forwarded progression from (e.g.) scum to crawling fish to giant dinosaurs to us humans. Few non-specialists appreciate the complex, sometimes convoluted, multi-dimensional aspects of life's history on earth.

I'd like to believe that at some point in the future (assuming our species has one ... ) taxonomy per se will recede in importance (e.g., maintained only as a quaint indexing scheme) and there will have arisen some new model or account that better represents the process / plot rather than the characters in isolation.
 

oldrover

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Taxonomy is a double-edged sword. On the one hand, it's a great aid for sorting and making sense of things. On the other hand, premature commitments to categorization can problematically bias subsequent interpretation / incorporation of new data. With respect to evolution (or similar ongoing processes) it can only ID the waypoints, and it offers little value in understanding the course of events that comprise the 'real story'.

Unfortunately, we can interrogate the past only through its surviving evidence, leaving us with a set of found items whose interrelationships we can only imagine. It's like seeing a movie only in terms of widely-separated little glimpses. You can lay out the cast of characters spied within those glimpses, but you can never be sure what happened to or among them along the way. Even worse - you can't be sure you've even seen all the characters!

In the mean time, the general population tends to think of evolution in simplistic terms - e.g., a fairly linear path condensed into a fast-forwarded progression from (e.g.) scum to crawling fish to giant dinosaurs to us humans. Few non-specialists appreciate the complex, sometimes convoluted, multi-dimensional aspects of life's history on earth.

I'd like to believe that at some point in the future (assuming our species has one ... ) taxonomy per se will recede in importance (e.g., maintained only as a quaint indexing scheme) and there will have arisen some new model or account that better represents the process / plot rather than the characters in isolation.

Add hybridisation to that too, instead of a tree of life with nice diverging twigs they'd be very, very tangled. We're all hybrids. But then that leads to the questions about what constitutes a species in the first place. Apparently at present there are about six current models in mainstream use today.
 

EnolaGaia

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Agreed ... That's another reason I suspect some other overall reference model / scheme will eventually supplant, or at least augment, our current version of taxonomy.
 

EnolaGaia

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A newly published study offers (as far as I've seen over the last 4 decades) the most comprehensive reconstruction of how the K-T boundary asteroid event affected the atmosphere, weather, and the prospects for both animals' and plants' survival.

The authors' statement of significance reads as follows:
... A worldwide layer of soot found at the boundary is consistent with global fires. Using a modern climate model, we explore the effects of this soot and find that it causes near-total darkness that shuts down photosynthesis, produces severe cooling at the surface and in the oceans, and leads to moistening and warming of the stratosphere that drives extreme ozone destruction. These conditions last for several years, would have caused a collapse of the global food chain, and would have contributed to the extinction of species that survived the immediate effects of the asteroid impact.

News Article Summarizing the Published Study:

http://www.livescience.com/60217-dino-killing-asteroid-caused-two-years-of-darkness.html

Study's Abstract (and full text if you have access):

http://www.pnas.org/content/early/2017/08/15/1708980114
 

EnolaGaia

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This article summarizes a new study offering evidence suggestive of the interplay between the Chicxulub impact and the Deccan Traps eruptions. It also takes into account the possibility of aggravated volcanic activity along the mid-ocean ridges (the boundaries among tectonic plates). I think this is the first time anyone's correlated impact and volcanic aspects of the K-T boundary event with regard to physical evidence (as opposed to generally coincident timing). I also believe this is the first time anyone's provided evidence supporting the notion that oceanic / seafloor volcanic activity played a significant role.

The Meteorite That Killed the Dinosaurs May Have Also Triggered Underwater Volcanoes
The end of the Cretaceous period 66 million years ago was a rough time to be living on Earth.

Three global catastrophes occurred nearly simultaneously: The Chicxulub meteorite slammed into what is now Mexico’s Yucatan Peninsula, the massive Deccan Traps volcanic province in modern-day India erupted, and some three-quarters of Earth’s plants and animals, including all non-avian dinosaurs, went extinct. The occurrence of these three events at the same time in our planet’s history has fueled a decades-long debate about causal links. Either a large sequence of volcanic eruptions or an extraterrestrial impact could conceivably cause a mass extinction – but were they all somehow connected?

As Earth scientists, we have reason to believe that there may be another event to add to the list. Our new research, published in Science Advances, shows that the Chicxulub impact may have triggered additional volcanic activity far from the Deccan Traps – along tens of thousands of miles of undersea volcanic ridges that lie at the edges of tectonic plates. The meteorite impact caused large seismic waves that traveled around the globe and were apparently capable of flushing magma out of the mantle and into the oceanic crust. This would presumably be more bad news for the dinosaurs and other flora and fauna of the time. ...

FULL ARTICLE: https://www.smithsonianmag.com/scie...e-nature+(Science+&+Nature+|+Smithsonian.com)
 

ramonmercado

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eburacum

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I think this is the first time anyone's correlated impact and volcanic aspects of the K-T boundary event with regard to physical evidence (as opposed to generally coincident timing).
Maybe so, but there appears to be quite a good correlation between the Hellas Basin impact on Mars and the Tharsis volcanoes, so there does seem to be a connection between impacts and geological activity elsewhere in the Solar System. The Hellas impact was probably much bigger than Chicxulub, though.
 

AlienView

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No definitive answer? - IF using what is known, and most of the historical data is already known, has not given
a solid and provable answer to date - there is none.

So its time for the hypothetical AlienView.

The dinosaur experiment was finished - no further meaningful results could be obtained simply by increasing
size and power - We needed to go elsewhere and could not let the Planet Earth resources be wasted
by hugh beasts, who while interesting, were both bestial and inefficient.

Hence most dinosaur species were removed from planet Earth - And this allowed for the implantation of
other more meaningful species, and especially and eventually Man.

The 'Genetic Experiment' that has been playing out since then is a matter of historical record.
 
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EnolaGaia

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Initial results are being evaluated and reported from the project drilling into the Chicxulub crater. This news item summarizes the evidence for one extremely violent day's events.
Ancient Rock Reveals Shocking First Day After Dinosaur-Killing Asteroid Impact

Scientists say they have spotted evidence of what it was like on the first day after the dinosaur-killing impact event, thanks to an analysis of rock taken from the famous Chixculub crater.

... Rock cores recently taken from the resulting crater show evidence of hills, tsunamis, fires, and atmosphere-altering gases, all produced in the first day after the impact.

“It’s so rare in geology that we get to look at the rocks and read a story on the timescale of hours,” Sean Guelick, the study’s first author from the University of Texas at Austin, told Gizmodo.

The impact probably went as follows, based on the rock samples and what we already know about the area surrounding the crater. Initially, the site of the impact was shallow ocean, less than 100 feet deep. An enormous rock, perhaps a few miles wide, struck and immediately created a large crater. The meteorite would have welled up rock that then collapsed outward, creating a hilly ring. Soon, the ring would have been covered by more than a hundred feet of so-called shocked rock, deformed by the high heat and pressure. The ocean would then have filled the crater, depositing any debris it was carrying. Finally, the wave that flooded the land would return, depositing soil and other material it picked up from the shore. The process would have taken just hours, according to the paper published in the Proceedings of the National Academy of Sciences.

“You look at a meter of core, and typically you’re looking at millions of years of time. In this case, you instantly made a hole with the impact and buried it with all these dynamic processes,” Guelick said. ...

Perhaps most surprising were the soil and charcoal particles they found in the rock, evidence that a tsunami returned to the site of the impact from shore. “It speaks to the energy of the impact,” Katherine Freeman, one of the study’s authors and a professor at Penn State, told Gizmodo. She explained that the patterns in the charcoal were complex, so it’s not as easy as simply saying there were forest fires, but the charcoal was suggestive of high-energy heating that took place hundreds of miles away.

This research doesn’t immediately offer an explanation to how the impact led to a mass extinction. However, the core seemed to be missing sulfur, Guelick said. This could mean that the impact released the sulfur into the atmosphere. A mass extinction would require planetwide catastrophe, and a quick addition of sulfur and other molecules to the atmosphere could have caused global cooling and darkness. ...
FULL STORY: https://gizmodo.com/ancient-rock-reveals-shocking-first-day-after-dinosaur-1837991356
 

EnolaGaia

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New research indicates the Chicxulub (K-Pg Boundary) impact resulted in an immediate acidification of the surrounding ocean(s). This new finding fills in a missing piece of the catastrophic after-effects. Although it had long been believed the die-off of marine life was largely caused by radical acidification of the seas, this acidification was presumed to have taken a long time and resulted from some sort of secondary effect (e.g., massive vulcanism).

That Dinosaur-Killing Asteroid Instantly Acidified Our World's Oceans, Too

We know that the Chicxulub impactor was responsible for the extinction of the land-based dinosaurs when it slammed into Earth some 66 million years ago. But new research shows the asteroid severely acidified the oceans too, wiping out much of the life residing underwater.

It's the first direct evidence scientists have found that the dino-destroying impact was also to blame for the instant acidification of the waters – enough to prompt a mass extinction that should act as a warning for us today.

Significant amounts of marine life were wiped out by the Chicxulub asteroid, the researchers say; it seems there wasn't a gradual build-up of acid levels caused by volcanic activity, as had been previously hypothesised.

"Our data speaks against a gradual deterioration in environmental conditions 66 million years ago," says geochemist Michael Henehan, from the GFZ German Research Centre for Geosciences. "Before the impact event, we could not detect any increasing acidification of the oceans."

"The ocean acidification we observe could easily have been the trigger for mass extinction in the marine realm," says geologist Pincelli Hull, from Yale University in Connecticut. ...

FULL STORY: https://www.sciencealert.com/the-di...extinction-by-instantly-acidifying-the-oceans

See Also:
https://www.sciencedaily.com/releases/2019/10/191022080721.htm
 

EnolaGaia

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The full report on this latest research is accessible at PNAS:

https://www.pnas.org/content/early/2019/10/15/1905989116

Here's the Significance statement from the online publication ...

Significance
Debate lingers over what caused the last mass extinction 66 million years ago, with intense volcanism and extraterrestrial impact the most widely supported hypotheses. However, without empirical evidence for either’s exact environmental effects, it is difficult to discern which was most important in driving extinction. It is also unclear why recovery of biodiversity and carbon cycling in the oceans was so slow after an apparently sudden extinction event. In this paper, we show (using boron isotopes and Earth system modeling) that the impact caused rapid ocean acidification, and that the resulting ecological collapse in the oceans had long-lasting effects for global carbon cycling and climate. Our data suggest that impact, not volcanism, was key in driving end-Cretaceous mass extinction.
 

Kondoru

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Old rover is right, the dinosaura still rule the world, but only the small, fluffy, fashionable ones.

I think the other taxons died out because they were unfashionable.
 

EnolaGaia

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Other pieces of the puzzle are falling into place. It appears that the earlier, massive and long-lasting Deccan Traps eruptions served as the source for dramatically increased mercury levels evident from strata and fossils worldwide.
Earth's Atmosphere Had Terrifying Mercury Pollution Even Before The Killer Asteroid

Even before the Chicxulub asteroid hit Earth 66 million years ago, dinosaurs and other life forms were dealing with toxic mercury levels, a new study suggests.

The fresh evidence serves up even more contention in a "long-running and bitter" debate over how the dinosaurs died all those years ago. While some scientists blame their demise solely on the notorious asteroid that hurtled into our planet, others maintain there's more to the story.

Violent volcanic eruptions began at least tens of thousands of years before the asteroid impact, and it's thought all that lava could have exacerbated the impact of the cataclysmic event that claimed three-quarters of all life on Earth.

Examining ancient fossilised bivalves from around the world, scientists have now pinned a global increase in mercury and carbon dioxide on a series of long-lived eruptions that formed the feature now known as the Deccan Traps. These events lasted for nearly a million years and formed much of western India during the Cretaceous-Paleogene mass extinction. ...

Mercury is a toxic trace chemical, and volcanic eruptions are the largest producer of it here on Earth. When this element makes its way into the ocean, it becomes highly reactive with organic matter and is readily taken up by phytoplankton, which mollusks then eat.

Using their shells as an indicator of water quality and temperature, scientists now think the Deccan Traps eruptions had profound, long-lasting and global climatic and ecological impacts.

"Mercury anomalies had been documented in sediments but never before in shells," says geochemist Sierra Petersen from the University of Michigan.

"Having the ability to reconstruct both climate and a volcanism indicator in the exact same materials helps us circumvent lots of problems related to relative dating."

Sediment records, for example, are limited because they have not yet linked mercury emissions to global climate changes; the new study was able to do just that. ...
FULL STORY: https://www.sciencealert.com/earth-...before-the-asteroid-that-killed-the-dinosaurs
 

EnolaGaia

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The debate over the primary cause of the dinosaurs' extinction has entered a new round. Recently published research by multiple teams from multiple nations indicates the massive Deccan Traps vulcanism event(s) occurred too early and affected global temperatures too little to be blamed.

This article focuses on the study's lead author / team at Yale ...
In death of dinosaurs, it was all about the asteroid -- not volcanoes

Summary:
Volcanic activity did not play a direct role in the mass extinction event that killed the dinosaurs, according to an international team of researchers. It was all about the asteroid.

Volcanic activity did not play a direct role in the mass extinction event that killed the dinosaurs, according to an international, Yale-led team of researchers. It was all about the asteroid.

In a break from a number of other recent studies, Yale assistant professor of geology & geophysics Pincelli Hull and her colleagues argue in a new research paper in Science that environmental impacts from massive volcanic eruptions in India in the region known as the Deccan Traps happened well before the Cretaceous-Paleogene extinction event 66 million years ago and therefore did not contribute to the mass extinction.

Most scientists acknowledge that the mass extinction event, also known as K-Pg, occurred after an asteroid slammed into Earth. Some researchers also have focused on the role of volcanoes in K-Pg due to indications that volcanic activity happened around the same time.

"Volcanoes can drive mass extinctions because they release lots of gases, like SO2 and CO2, that can alter the climate and acidify the world," said Hull, lead author of the new study. "But recent work has focused on the timing of lava eruption rather than gas release."

To pinpoint the timing of volcanic gas emission, Hull and her colleagues compared global temperature change and the carbon isotopes (an isotope is an atom with a higher or lower number of neutrons than normal) from marine fossils with models of the climatic effect of CO2 release. They concluded that most of the gas release happened well before the asteroid impact -- and that the asteroid was the sole driver of extinction.

"Volcanic activity in the late Cretaceous caused a gradual global warming event of about two degrees, but not mass extinction," said former Yale researcher Michael Henehan, who compiled the temperature records for the study. "A number of species moved toward the North and South poles but moved back well before the asteroid impact." ...
FULL STORY: https://www.sciencedaily.com/releases/2020/01/200116141708.htm
 

EnolaGaia

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This BBC article focuses on an affiliated team in the UK.
Dinosaur extinction: 'Asteroid strike was real culprit'

Was it the asteroid or colossal volcanism that initiated the demise of the dinosaurs 66 million years ago?

This has been a bit of a "to and fro" argument of late, but now a group of scientists has weighed in with what they claim is the definitive answer.

"It was the asteroid 'wot dun it'!" Prof Paul Wilson told the BBC.

His team's analysis of ocean sediments shows that huge volcanoes that erupted in India did not change the climate enough to drive the extinction. ...

(T)he Deccan Traps, as the volcanic terrain in India is known, certainly had massive scale - hundreds of thousands of cubic km of molten rock were erupted onto the land surface over thousands of years.

But the new research from Southampton University's Prof Wilson, and colleagues from elsewhere in Europe and the US, indicates there is a mismatch in both the effect and timing of the volcanism's influence.

The group drilled into the North Atlantic seafloor to retrieve its ancient muds.

"The deep ocean sediments are packed full of these microscopic marine organisms called Foraminifera," Prof Wilson explained.

"You get about a thousand of them in a teaspoon of sediment. And we can use their shells to figure out the chemistry of the ocean and its temperature, so we can study in great detail the environmental changes that are occurring in the run-up to the extinction event.

"And what we discovered is that the only way in which we can get our (climate) model simulations to match the observed temperature changes is to have the volcanic emissions of harmful gases done and dusted a couple of hundred thousand years before the impact event.

"We find the impact event is exactly contemporaneous with the extinction." ...

FULL STORY: https://www.bbc.com/news/science-environment-51150001
 

EnolaGaia

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The 'impact winter' triggered by the Chicxulub strike played a larger role than expected in facilitating the resultant extinctions, and the soot lofted by the strike is now believed to have been more important than previously suspected.
After the Dinosaur-Killing Impact, Soot Played a Remarkable Role in Extinction

The famous impact 66 million years ago kicked up soot into the atmosphere that played an even bigger role in blocking sunlight than experts had realized

The interstellar object (alternatively a comet or an asteroid) that killed the dinosaurs when it slammed into Earth didn't work alone. Researchers have shown previously that its after-effects, such as tidal waves and earthquakes, played an important role in the mass extinctions of three-fourths of plant and animal life. Now, new research suggests that one of the most important factors was the soot-rich smoke from fires sparked by the collision. ...

When the impactor plowed into the Earth and created the Chicxulub crater in Mexico, it vaporized the crust and created a planet-wide plume of debris that emitted radiation at a rate about 20 times stronger than the sun. It ignited plants and animals in its path. Later, lightning from impact-generated storms ignited more fires, maintaining an atmosphere rich in soot. ...

The soot was the death knell for many marine creatures. While oceans protected them from blazes, the soot remained in the atmosphere to block most sunlight for nearly two years, darkening the skies and preventing photosynthesis. The new calculations suggest that it took almost six years for sunlight levels at the surface to return to normal, hindering recovery and leading to mass marine extinctions.

"Soot blocked sunlight, greatly reducing if not shutting down photosynthesis on both the land and in the sea" ... "Without photosynthesis, the base of the food chain would have collapsed. While fires may have demolished vegetation on land in large areas of the world, globally distributed soot may have ravaged vegetation elsewhere." ...
FULL STORY: https://www.smithsonianmag.com/science-nature/soot-dinosaur-impact-180974708/

PUBLISHED REPORT: https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2019GL085572
 

Ladyloafer

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just randomly browsing through my bookshelves and upon my copy of Reader Digest Strange Stories and Amazing Facts , i opened it on No Room in the Ark; how did the dinosaurs die?

theories include; lemming like mass suicide due to boredom, cosmic radiation, and dino egg-eating mammals. it concludes it was probably a combination of eggshell thinning and a cooler climate. without body hair or feathers to protect, they got too cold. also poison flowers, which killed the herbivores and hence the predators.

whilst amusing i also found it astonishing that 'only' 45 years ago, when this book was published, there is no mention of asteroid impact.
astonishing because this is such a common and well known FACT that its hard for me to get my head around the idea that within my lifetime this was an unknown.

yeah i know science and knowledge is constantly changing and adapting and discovering, it just feel like Asteroid strike killed the dinosaurs has always been known o_O
 
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