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02 Apr 2019 04:36

midtskogen wrote:
Source of the post Very interesting, though I've never liked the hypothesis that the extinctions happened in a few years rather than in millennia or even a million years.

Very interesting, indeed.  And I agree with your skepticism, though am also reminded of the old geologists, who (for admittedly good reasons at the time), did not like catastrophism, or the notion that large geologic events happened very rapidly.  Even the idea that craters or extinctions were caused by rocks falling out of the sky was once thought ridiculous.

In this case I don't think the idea that impact-generated extinction could be that rapid is too ridiculous.  We know the effects were very dramatic, affected the whole world within hours, and were also short-lived.  But at the same time the story of the findings by this scientist and his interpretations does sound too good to be true.  As usual I'll wait to see what the rest of the geological community makes of it. :)
 
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02 Apr 2019 12:55

It's been known for a while that there was an impact due to the iridium found in the KT layer, so the asteroid hypothesis has been around for some time.  The trouble with catastrophic explanations is that something "sudden" in geological terms usually means many thousand years, so something happening in days or a few years is not necessary to explain something.  Few dispute that there was an asteroid impact, but the question is: was it the only cause of extinction?  I'm reluctant to rule out a more complex explanation, but the Chicxulub crater gives an idea of the size of the event, and if conclusive fossil evidence for sudden mass dying can be provided, I'll happily change my mind.  If the impact was the single cause, it's quite exciting, but for precisely that reason it also needs clear evidence.
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02 Apr 2019 23:57

midtskogen wrote:
Direct evidence for sudden KT extinction? Very interesting, though I've never liked the hypothesis that the extinctions happened in a few years rather than in millennia or even a million years.

That was a very interesting article midtskogen. Thank you for linking it. I always knew that something wonderful was buried in Hell Creek (well, terrible for the dinosaurs, but an absolute treasure for paleontologists).

It has been discussed elsewhere on the forum that the dinosaurs would have probably survived other extinction-level events, like ice-ages and the Deccan supervolcanic eruptions. Cumulatively however, the global cooling, climate change thereof and the various volcanic disturbances around the world weakened the ecology of the ancient archosaurs to such an extent that couple with this asteroid impact, they did not stand a chance of recovering, even if there were dinosaur-survivors in the few years immediately after the impact (which there certainly were). It was the final nail in the coffin, and these findings seemingly prove it. More research will doubtless be needed before this is irrefutable fact, and DePalma was right to keep this hushed until now to gain an edge on his competitors. Open-access to evidence is indeed a hallmark of good science, but as a 1890 issue of the New York Herald once stated: “Scientists Wage Bitter Warfare.
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08 Apr 2019 09:30

Stellarator wrote:
midtskogen wrote:
Direct evidence for sudden KT extinction? Very interesting, though I've never liked the hypothesis that the extinctions happened in a few years rather than in millennia or even a million years.

That was a very interesting article midtskogen. Thank you for linking it. I always knew that something wonderful was buried in Hell Creek (well, terrible for the dinosaurs, but an absolute treasure for paleontologists).

It has been discussed elsewhere on the forum that the dinosaurs would have probably survived other extinction-level events, like ice-ages and the Deccan supervolcanic eruptions. Cumulatively however, the global cooling, climate change thereof and the various volcanic disturbances around the world weakened the ecology of the ancient archosaurs to such an extent that couple with this asteroid impact, they did not stand a chance of recovering, even if there were dinosaur-survivors in the few years immediately after the impact (which there certainly were). It was the final nail in the coffin, and these findings seemingly prove it. More research will doubtless be needed before this is irrefutable fact, and DePalma was right to keep this hushed until now to gain an edge on his competitors. Open-access to evidence is indeed a hallmark of good science, but as a 1890 issue of the New York Herald once stated: “Scientists Wage Bitter Warfare.

I would also like to find out if we can link this mass extinction event to others, like the Permian.  Are these super mass extinction events truly periodic and does the sun's path around the center of the Milky Way influence these events?
 
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09 Apr 2019 00:30

A-L-E-X wrote:
Source of the post I would also like to find out if we can link this mass extinction event to others, like the Permian.

No, the Permian mass extinction was almost certainly exclusively the work of supervolcanic eruptions in Siberia known as the Siberian Traps. There was cursory evidence of 'shocked quartz' in the continental strata of Australia/Antarctica suggestive of an asteroid impact from that time, but this evidence is challenged by its outdated methods of detection. Whatever the case may be, supervolcanoes don't seem to follow a pattern of any sort, aside from that of short-term tectonic shifts.

A-L-E-X wrote:
Source of the post Are these super mass extinction events truly periodic and does the sun's path around the center of the Milky Way influence these events?

No, they are not periodic. If traced on a timeline, it may seem like events like these are superficially so, but in actuality the events have little in common with one another. The only cyclic extinction-level events may be those of large asteroid impacts, since one the size of the Chicxulub impactor (the one that finished off all non-avian dinosaurs) strikes about every 100 million years or so, one slightly smaller strikes at around 50 million years or so and so forth. These NEOs obviously orbit the sun like the Earth, and so have a cyclic nature in relation to our planet. The trouble here with this theory is that the vast majority of those asteroids and comets, even those of the size of the K/T impactor, are alone not enough to truly count as extinction-level events when they hit (though they ARE quite devastating). To qualify as deadly, they need to hit in a particularly sedimentary deposit or shallow sea, and in sequence with other natural disasters which have already weakened the local ecology (during the Late Cretaceous, those were the Deccan Traps blowing some hundreds of thousands of years before the Chicxulub steroid impact).

Aside from that, it is difficult to say what may be cyclic and what is not in terms of extinction, since the overall fossil record, especially that which is older then 500 million years, is incomplete at best.

A-L-E-X wrote:
Source of the post and does the sun's path around the center of the Milky Way influence these events?

Probably not as much as one would think, since the chances of the sun being in the danger zone of a supernova explosion or a gamma ray burst during its 250 million year orbit roughly on the galactic plane is pretty slim. That being said, there are various extinctions attributed to interstellar trouble, the most recent of which is the Pleistocene extinction of 2.6 million years ago, in which a supernova 150 light-years away is possibly linked to the great dying of many Earth megafauna, especially shallow marine animals like the massive Carcharocles megalodon shark. This dying off of the megafauna is attributed to increased risk of cancer (up to 50%) in those creatures from fast moving muon particles released by the supernova. Smaller creatures seemed ansorb less of the particles, and thus escape harm.
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09 Apr 2019 14:20

That's fascinating!  Have one of our big mass extinction events also been linked to a gamma ray burst?   The Ordovician-Silurian mass extinction is mentioned as one that may have been caused by a GRB. 

https://arxiv.org/abs/0809.0899

 As far as the closest star that we know of that may go supernova in the future, that would be Betelgeuse, though the timescale of that happening is uncertain.  How bad would the effects be here if it did? 

About supervolcano eruptions, is there any connection between them and impact events?


Reading through all these https://en.wikipedia.org/wiki/Extinction_event#Patterns_in_frequency

Although each mass extinction had its own causes, there does seem to be a relationship between the different extinction stimuli, since no one cause can be attributed to a single mass extinction, rather there seems to have been a chain reaction with the mass extinction as the ultimate result.

Some evidence for periodicity:

https://www.cambridge.org/core/journals ... 284E9CAA3F

https://arxiv.org/abs/1005.4393


https://arxiv.org/abs/1206.1804

https://www.nature.com/articles/nature03339

And some info on the sixth mass extinction that's now underway.

https://www.youtube.com/watch?v=z9gHuAwxwAs

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5544311
 
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10 Apr 2019 01:04

A-L-E-X, I have answered your questions regarding mass extinctions, supernovas etc in the Science & Astronomy Questions thread.
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10 Apr 2019 01:24

The titles say it all:


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13 Apr 2019 02:04

This discovery was probably "eclipsed" by the hype surrounding the recent M87 blackhole image, but the TESS satellite (Transiting Exoplanets Survey Satellite) has discovered the first direct evidence of an exocomet (or even two whole families of them!), orbiting the young star Beta Pictoris 63 light-years away. This star and its burgeoning orbital clouds is well-known in astronomical circles for being a rich source of solar-system formation data.  The success of TESS in its discoveries cannot be overstated:

https://www.eso.org/public/archives/releases/sciencepapers/eso1432/eso1432a.pdf

https://arxiv.org/pdf/1903.11071.pdf

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14 Apr 2019 01:06

Yet more space news concerning exoplanets (this week has been a busy one!):

A second planet some 6 times the mass of Earth may have been spotted orbiting our closest neighboring star, Proxima Centauri. Remembering the false-detection of a planet orbiting Alpha Cen. B, I remain cautious about accepting this for the moment, but it seems like the Proxima system is indeed a busy one.

https://www.scientificamerican.com/article/a-second-planet-may-orbit-earths-nearest-neighboring-star/

https://www.space.com/proxima-centauri-possible-second-exoplanet.html

https://news.nationalgeographic.com/2016/08/earth-mass-planet-proxima-centauri-habitable-space-science/
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14 Apr 2019 02:04

Stellarator wrote:
Source of the post this week has been a busy one!

Yes.  Also worthy mentions are the Falcon Heavy launch with recovery of all boosters, and the Israeli crash on the Moon.
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15 Apr 2019 15:45

Stellarator wrote:
Yet more space news concerning exoplanets (this week has been a busy one!):

A second planet some 6 times the mass of Earth may have been spotted orbiting our closest neighboring star, Proxima Centauri. Remembering the false-detection of a planet orbiting Alpha Cen. B, I remain cautious about accepting this for the moment, but it seems like the Proxima system is indeed a busy one.

https://www.scientificamerican.com/article/a-second-planet-may-orbit-earths-nearest-neighboring-star/

https://www.space.com/proxima-centauri-possible-second-exoplanet.html

https://news.nationalgeographic.com/2016/08/earth-mass-planet-proxima-centauri-habitable-space-science/

So now we have two planets around Promixa? :) I just wish that star was more magnetically stable so there was a chance of it having habitable worlds!  Or maybe the main star of the system has them and we just haven't detected them yet!  It's the most sunlike star we know of!
 
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16 Apr 2019 02:29

A-L-E-X wrote:
Source of the post Or maybe the main star of the system

Alpha Centauri itself is a binary system, comprised of the primary star Rigil Kentaurus (a G2V type sun 10% more massive then Sol) and it`s sister Toliman (A K2V type sun about 90% the mass of Sol) who circles the systems barycenter at a perihelion distance of 11.2 AU (1.68 billion km) and a aphelion distance of 35.6 AU (5.33 billion km). Each could have a possible small solar-system orbiting them, though the likelihood of a planet being habitable in one is uncertain due to the closeness of the binary system.
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19 Apr 2019 15:10

Thanks for the graphs!  I've always wondered what shadows would look like in multiple star systems- especially with different colored stars!
 
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20 Apr 2019 16:19

A-L-E-X wrote:
Source of the post I've always wondered what shadows would look like in multiple star systems- especially with different colored stars!

Space Engine is a good way to experience it. :)

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