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Old 04-05-2018, 06:41 PM
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Dinosaurs, asteroids and extinctions.


We're told that an asteroid killed off the dinosaurs. We're also told (I think) that the Cretaceous-Paleogene extinction event lasted something like 10,000 years.

I understand that a cataclysmic meteoric impact would create a 'long winter', but my understanding is that that would last a few years, not a few thousand years.

Am I wrong about the duration of the extinction event? Am I wrong about the duration of the long winter? How exactly does such a quick event cause such an extended extinction event?
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Old 04-05-2018, 07:38 PM
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The Cretaceous–Paleogene (K–Pg) extinction event did occur over a duration of at leaste a few millenia; there are debates over exactly when it ended, but the start is widely held to correspond with a thin layer of iridium-containing sediment which is not generally found in the Earth’s crust. Although the event probably did cause a world wide winter due to dust thrown up into the Earth’s atmosphere that may have lasted several years or possibly a decade, the real cause of mass extinction was the widespread effects on photosynthetic life and a resulting reshuffling which favored species and clades which were more adaptable. This occurred across all kingdoms but particularly affected the megafauna which predominately consisted of dinosaurs which were consisted of both reptilian species and pre-avian species. The smaller and more adaptable aves and reptiles survived but the class of warm-blooded creatures in the class Mammalia suddenly came into their own in the scavenging environment of post-apocalyptic new era and competed and grew into existing and new environmental niches including flying animals (bats), Pleistocene and Eocene terrestrial megafauna (unglate herbivores; canine-, feline-, and hyena-like obligate carnivores, and ursines), and the variety of marine mammals which came from diverse paths of terrestrial mammals. Euarchontoglires, including primates, stayed small until much later.

So while the climate effects of the initial impact only lasted for a few years or perhaps a couple of decades, the downstream effects on evolutionary fitness on both microfauna and macrofauna due to the impact on photosynthetic flora had long ranging impact upon all life on Earth for thousands of years and altered the course of evolutionary development by disrupting the existing homeostatis. And we are statistically due (according to some, overdue) for another impact of comparable size and destructive capability. Consider that next time you hear politicians arguing to spend money on weapons and wars, or whether to allocate a paltry few billion dollars to planetary exploration or solar orbiting satellite mission.

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Old 04-05-2018, 08:05 PM
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Or to put it much more succinctly, ecology is complicated, and it can take a long time for all of the indirect effects to work themselves out.
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Old 04-05-2018, 11:20 PM
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There is some evidence that extinctions were already underway when the asteroid hit. The speculated cause was a period of climate change starting a million years prior to the impact, possibly as a consequence of massive continental volcanism in India (the Deccan Traps). In this variation, the asteroid impact definitely finished off the dinosaurs, but they were already declining.
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Old 04-06-2018, 05:41 AM
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Quote:
Originally Posted by Smudge777 View Post
We're told that an asteroid killed off the dinosaurs. We're also told (I think) that the Cretaceous-Paleogene extinction event lasted something like 10,000 years.
I don't know the specific source of the 10,000 years claim, but it could mean "no longer than 10,000 years, but possibly a couple of months." What we know about the timings of extinctions is fuzzy thanks to Signor Lipps* and the raw number of years in "fuzzy" gets larger the further back in time you go thanks to error bars on dating methods.


*(Which I've always thought should have a mascot similar to one of the Four Hearseman of the Alpaca Lips, just a punk eek should have a variety of this guy.)
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Old 04-06-2018, 06:16 AM
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Originally Posted by nachtmusick View Post
There is some evidence that extinctions were already underway when the asteroid hit. The speculated cause was a period of climate change starting a million years prior to the impact, possibly as a consequence of massive continental volcanism in India (the Deccan Traps). In this variation, the asteroid impact definitely finished off the dinosaurs, but they were already declining.
That sort of "one-two punch" is speculated to be a common cause of extinction as I recall. One problem causes a decline in a species, and before it can recover another comes along and exterminates it entirely.
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Old 04-06-2018, 06:24 AM
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That sort of "one-two punch" is speculated to be a common cause of extinction as I recall. One problem causes a decline in a species, and before it can recover another comes along and exterminates it entirely.
If I recall correctly, the vast majority of dinosaur species that ever existed were either extinct or well into a decline by the time the asteroid is believed to have struck. As I recall this conclusion is reached by analyzing the volume and variety of the fossil record, which seems to have entered a precipitous decline by the time of the asteroid event 65 million years ago.

As others have pointed out, the asteroid itself would have had an initial major impact lasting several years. But the secondary effects due to loss of plant diversity and collapse of food chains would have had an impact that lasted well beyond that time - perhaps thousands of years.
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Old 04-06-2018, 07:17 AM
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What I find most fascinating is that, while this extinction event is the best known, it is by no means the worst!

That would be "the Great Dying":

https://en.wikipedia.org/wiki/Permia...tinction_event

The vast majority of life on Earth went extinct (96 percent of all marine species died out).

Allegedly, it was so bad, life took 10 million years to recover to previous levels.
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Old 04-06-2018, 02:51 PM
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T. Rex and the Crater of Doom

This is a book I found interesting. It discusses in some detail how the evidence let to the asteroid impact theory.
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Old 04-06-2018, 03:02 PM
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T. Rex and the Crater of Doom

This is a book I found interesting. It discusses in some detail how the evidence let to the asteroid impact theory.
Another good one is Night Comes to the Cretaceous.
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Old 10-04-2018, 08:03 AM
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Originally Posted by nachtmusick View Post
There is some evidence that extinctions were already underway when the asteroid hit. The speculated cause was a period of climate change starting a million years prior to the impact, possibly as a consequence of massive continental volcanism in India (the Deccan Traps). In this variation, the asteroid impact definitely finished off the dinosaurs, but they were already declining.

The Deccan volcanic flows started say ~250,000 years before the asteroid hit and continued till ~500,000 years after.

http://www.sci-news.com/geology/scie...ion-02345.html

The exact duration of the biggest flows/eruption and dates vary based on the study.

Quote:
Recent studies indicate that Deccan volcanic eruptions occurred in three main phases with the initial and smallest Phase-1 at ~67.4 Ma; the relatively short main Phase-2 with ~80% of total Deccan volume ends in C29r below the KT boundary; and the last Phase-3 at the base of C29n in the early Danian .., about 280 ky after the Cretaceous-Tertiary boundary (KTB) mass extinction
https://massextinction.princeton.edu...enture-science

So it looks as if the Deccan /reunion hotspot flow kept beating up the environment, starting maybe 250,000 years before, landed heavy punches before the extinction, and the largest haymakers around the time of the extinction and again ~ 280,000 years later

Combined with chicxulub, that's a powerful kick towards extinction

Last edited by barath_s; 10-04-2018 at 08:04 AM. Reason: Format
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Old 10-04-2018, 11:22 PM
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... it can take a long time for all of the indirect effects to work themselves out.
Indeed and evolution being what it is, they likely still working themselves out.
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