Asteroid Dust Found in Crater Closes Case of Dinosaur Extinction (phys.org) 56
Phys.org shares an announcement from the University of Texas at Austin:
Researchers believe they have closed the case of what killed the dinosaurs, definitively linking their extinction with an asteroid that slammed into Earth 66 million years ago by finding a key piece of evidence: asteroid dust inside the impact crater.
Death by asteroid rather than by a series of volcanic eruptions or some other global calamity has been the leading hypothesis since the 1980s, when scientists found asteroid dust in the geologic layer that marks the extinction of the dinosaurs. This discovery painted an apocalyptic picture of dust from the vaporized asteroid and rocks from impact circling the planet, blocking out the sun and bringing about mass death through a dark, sustained global winter — all before drifting back to Earth to form the layer enriched in asteroid material that's visible today. In the 1990s, the connection was strengthened with the discovery of a 125-mile-wide Chicxulub impact crater beneath the Gulf of Mexico that is the same age as the rock layer.
The new study seals the deal, researchers said, by finding asteroid dust with a matching chemical fingerprint within that crater at the precise geological location that marks the time of the extinction... The telltale sign of asteroid dust is the element iridium — which is rare in the Earth's crust, but present at elevated levels in certain types of asteroids... In the crater, the sediment layer deposited in the days to years after the strike is so thick that scientists were able to precisely date the dust to a mere two decades after impact.
"We are now at the level of coincidence that geologically doesn't happen without causation," said co-author Sean Gulick, a research professor at the UT Jackson School of Geosciences who co-led the 2016 expedition with Joanna Morgan of Imperial College London...
The dust is all that remains of the 7-mile-wide asteroid that slammed into the planet millions of years ago, triggering the extinction of 75% of life on Earth, including all nonavian dinosaurs.
Death by asteroid rather than by a series of volcanic eruptions or some other global calamity has been the leading hypothesis since the 1980s, when scientists found asteroid dust in the geologic layer that marks the extinction of the dinosaurs. This discovery painted an apocalyptic picture of dust from the vaporized asteroid and rocks from impact circling the planet, blocking out the sun and bringing about mass death through a dark, sustained global winter — all before drifting back to Earth to form the layer enriched in asteroid material that's visible today. In the 1990s, the connection was strengthened with the discovery of a 125-mile-wide Chicxulub impact crater beneath the Gulf of Mexico that is the same age as the rock layer.
The new study seals the deal, researchers said, by finding asteroid dust with a matching chemical fingerprint within that crater at the precise geological location that marks the time of the extinction... The telltale sign of asteroid dust is the element iridium — which is rare in the Earth's crust, but present at elevated levels in certain types of asteroids... In the crater, the sediment layer deposited in the days to years after the strike is so thick that scientists were able to precisely date the dust to a mere two decades after impact.
"We are now at the level of coincidence that geologically doesn't happen without causation," said co-author Sean Gulick, a research professor at the UT Jackson School of Geosciences who co-led the 2016 expedition with Joanna Morgan of Imperial College London...
The dust is all that remains of the 7-mile-wide asteroid that slammed into the planet millions of years ago, triggering the extinction of 75% of life on Earth, including all nonavian dinosaurs.
Hot (Score:2)
There's another version of the asteroid theory, not cold, but hot [wnycstudios.org].
There's a much longer version you can watch on YouTube.
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You can have both. The heat is short lasting and more localised (even all the way up to Canada is still less than global), the cooling is going to stick around for quite some time.
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Not localized. The theory is that molten glass rained down on the entire surface of the planet (rock was vaporized, ejected into space, solidified, was pulled back down, and liquefied on its way back down through the atmosphere).
Wrong (Score:5, Funny)
https://img-9gag-fun.9cache.co... [9cache.com]
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Scientists have show that the moon is moving away at a tiny, although measurable, distance from the earth every year.
If you do the math, you can calculate that 85 million years ago the moon was orbiting the earth at a distance of about 35 feet from the earth's surface.
This would explain the death of the dinosaurs. . . the tallest ones, anyway. . .
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Please tell me you understood that was a joke.
Causation (Score:4, Insightful)
It wasn't the asteroid that killed all that life, though. It would have been the rapid climate change from all the dust in the atmosphere, no? Many organisms would not have been able to adapt quickly enough, especially large reptiles that can't regulate their body heat as well in a changing climate. Marine life would have been spared more than land-based organisms (which was the case).
That is not to say that a giant asteroid hitting the planet wouldn't have killed a lot of organisms on impact, through earthquakes, for example. This isn't just a semantic disagreement. Causation matters, in science and in life, in generation (whether it's a single cause or many). People seem to have a poor grasp on complex causality, which is one of the reasons we have things like conspiracy theories (not to get too off-topic).
Re: Causation (Score:2)
"in general" not "generation".
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I am also not a paleontologist, but I don't think that the placental mammals had evolved yet. At a minimum they were not yet widespread, marsupials were the primary if not only type of mammal besides the monotremes for the next several million years. That's why only marsupials and monotremes were found in Australia, it broke off before placental mammals arrived and set off on it's own journey across the nascent Indian Ocean. Humans and later dogs were the first placental mammals on the continent.
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Opossums are in North America.
Some theories think that marsupiuls evolved in N.A. when Pangaea was around and they traveled through Antarctica into Australsia.
Re:Causation (Score:5, Informative)
The land masses of the world were considerably closer together 65 million years ago. And the K-T boundary layer, with elevated levels of Iridium and soot from forest fires, has been found all over the world, including in New Zealand.
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It's doubtful that there's a single thing alive today that traces its ancestry to anything that lived in in what is now Arizona the day before the impact.
Chicxulub: Yucatan. What you're thinking of was 50,000 years ago.
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While that's true, the "hellfire raining from the heavens" thing is generally considered to be limited to 500-1000 miles away from the point of impact.
I believe there's a bit more headroom than that before you end up in orbit.
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Some of the more recent simulations have suggested that it is in fact the impact, or the immediate effects of the impact, that caused a large fraction of deaths. The impact sent huge amounts of material into orbit that started out blindingly hot. While quickly cooling, that material became incandescently hot again upon re-entering the atmosphere around the world. Much of the surface of the earth in the hours following impact have been likened to being in a pizza oven. The night sky would have become ill
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Certainly the shock wave, tsunamis, earthquakes and other direct effects of the asteroid impact would have killed a lot of organisms immediately or very soon after, but yes, the large scale extinction was caused by the climate effects from the vast amounts of dust sent up into the atmosphere. This would almost certainly wipe out most if not all of the megafauna within a few short years. The reason, I suppose, that avians and mammals survived is because they were smaller and their caloric requirements were h
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I wouldn't rule out aspiration of large amounts of iridium laden meteorite dust. Or the death of plants that formed the base of the food web, due to changes in sunlight. Mating grounds lost to sedimentation destroyed vast amounts of water creatures. Imagine all of the insects whose instars couldn't break out of the water because of floating fine dust covering their ponds and lakes. Not to mention migration cues and pathways disrupted and destroyed completely because the landscape and polarization of ligh
The Variables (Score:5, Insightful)
It seems perfectly reasonable to argue that an asteroid impact could generate rock dust that would be thrown in to the atmosphere.
It seems perfectly reasonable to argue that residue of rock dust at the Chicxulib crater is physical evidence that the asteroid which caused the crater generated dust.
But the kinetic energy of that asteroid striking the earth's surface would be a result of half the mass of the asteroid multiplied by the square of its velocity. We could generate a crater of the same size from a smaller asteroid moving more quickly. The article discusses that heightened levels of iridium, brought to the Earth by the asteroid, have been found "all around the world" at an equivalent time point in local geologic records, strongly suggesting that the dust raised by the Chicxulub impact was globe-spanning.
but we've seen evidence of volcanic ash spanning the globe. When Krakatoa erupted in 1883 the shockwave circled the Earth. When Mt St. Helens erupted in 1980, the dust had circled the globe within about two weeks [usgs.gov].
It definitely looks as though all the necessary elements have been found. But is this enough to account for everything? For example, this piece in the New Scientist [newscientist.com] points out that the fossil record in New Zealand shows dinosaurs there living on at least another million years after the Chicxulub impact.
Fascinating story, interesting to see where this goes... but very interested [and maybe just a tad sceptical] of the certainty of their findings...
I look at it like this (Score:1)
I look at it like this: We know an asteroid hit the earth creating a gigantic (150+km) crater 66 million years ago. It is a once-in-hundreds of millions of years kind of impact. We know that an impact creating such a crater, would have severe planet-wide effects. We know that 75% of species on earth became extinct very soon after (you could say "immediately" in geological scales). Putting 1+1 together tells me the probability that a rare event that can seriously affect life on earth, and the rare mass extin
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Yeah and you could have been dying of a heart attack the moment someone shot your heart. That's some great defence to a murder charge.
If a big ass asteroid like that hit the earth at the exact same time, you don't look for alternate causes. If there were volcanic eruptions, you look into how the asteroid caused them.
Re:I look at it like this (Score:4, Informative)
And the exact same thing can be caused by widespread volcanic eruptions changing the climate in the exact same way.
There's also a theory that the impact CAUSED widespread earthquakes and volcanic eruptions in the aftermath.
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And possibly the breakup of Gonwandaland, IIRC.
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Except that Gonwandaland broke up 180 million years ago.
Just google "earth 65 million years ago" to see mock-up maps.
Re:The Variables (Score:5, Interesting)
But the kinetic energy of that asteroid striking the earth's surface would be a result of half the mass of the asteroid multiplied by the square of its velocity. We could generate a crater of the same size from a smaller asteroid moving more quickly.
Not quite. Smaller high speed asteroids are likely to produce high altitude airburst - Something like Cheliabinsk 2013 or Tunguska. Higher the speed, higher the altitude at which it will disintegrate. Additionally, a lot of the fragments will burn out. More damage on the ground, less dust.
According to most models, Chicxulib was slow enough and big enough to reach the surface and throw into the atmosphere material from the bottom of the shallow sea which was there at the time. Depending on which model you take you are looking at anything up to several times of Chicxulib mass thrown into the atmosphere.
To put things into perspective - Chicxulib alone without the debris it threw from the ground is ~ 735 km^3. With the debris from the ground - anything up to 1000s of km^3.
Compared to that Minoan eruption ~ 50km^3m and temperature anomaly of ~ 2-5 degrees for more than a decade, Samalas ~ 30km^3 2-3 degrees for a decade and Krokotoa ~ 25km^3 and 1.5 degrees for a few years. It is the chill from those degrees that killed everything after Chicxulib, not the impact.
Re:The Variables (Score:4, Insightful)
We could generate a crater of the same size from a smaller asteroid moving more quickly.
Could we? The range of plausible asteroid impact velocities is not huge given that all asteroids (not comets) orbit in the same plane in close-to-circular orbits. The most likely impact velocity is 17 km/sec, and the distribution around that is not huge.
The article discusses that heightened levels of iridium, brought to the Earth by the asteroid, have been found "all around the world" at an equivalent time point in local geologic records, strongly suggesting that the dust raised by the Chicxulub impact was globe-spanning.
I would go with "demonstrating" not "strongly suggesting". Direct evidence can be taken as direct evidence. It is not "more scientific" to pretend that it isn't.
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points out that the fossil record in New Zealand shows dinosaurs there living on at least another million years after the Chicxulub impact. I have little dinosaurs running and flying around my back yard. I give them seeds, suet, and mealworm snacks,
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And speaking of that lot, it's probably time to put out another suet block for the woodpecker-saurs....
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We speak of the mammoths having died out 10,000 or so years ago, but a tiny population survived on Wrangel Island until 3,700 years ago. That doesn't negate the larger effect of climate change and more intense predation being responsible for their eventual extinction.
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Iridium is extremely rare on earth, so the volcanism theory cannot account for the quantity of it deposited around the world. There's just nowhere for it to have come from inside the earth. It is, however, relatively abundant in asteroids.
Tanis (Score:5, Informative)
I missed this story [wikipedia.org] when it came out in 2019. They claim they have a fossilized site from the day it happened.
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I apparently missed that as well.
If they're correct (and the indications seem to be to an amateur like me), that's an incredible find.
Thanks for sharing.
Case Closed (Score:2)
I keep hearing that this case has been closed over an over. I thought we established this a decade ago when we found the crater.
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correlation is not causation! (Score:2)
maybe it was the absence of dinosaurs that attracted the asteroid.
really makes you think, doesn't it.
Minor quibble. . . (Score:2)
. . . . dinosaurs survived. Just not many, and the Megafauna Dinosaurs went extinct. But there's an entire phyla of dinosaurs today, that have done fine.
We call them, 'birds'. (grin)
Not closed (Score:2)
I get what they are saying. But the slashdot author of the article is clearly a journalist and not a scientist. We don't proclaim "the science is settled and no further discovery is allowed here". We never do that. Well, actually a lot of people do, especially those who like to say "science says this" but don't actually understand the scientific method.
A lot of very "scientific" people sure knew a lot of science to prove the earth was the center of the universe. And it hampered further progress to say th
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That's actually not a very good example to use, since there was no actual evidence to demonstrate that Earth was the center of the universe, opposition came from the religious authorities (essentially the "anti-science" group). A better example would be the introduction of the germ theory rather than Galen's stupid "vital humors" hypothesis.
The impact alone didn't kill the Dinosaurs (Score:1)
The impact alone didn't kill the Dinosaurs, the impact caused the gravitation shift which lead to their extinction, while the Dinosaurs roamed the earth the gravitation force was lower which is how such large life forms were able to support themselves, after the impact when gravity was higher such large lifeforms could no longer support themselves.
And if you consider what caused the gravitational event, then it was probably a combination of the mass of the planet increasing and a closer orbit to the sun. In
Re: The impact alone didn't kill the Dinosaurs (Score:2)
Consider the mass ratio of the planet versus the asteroid (or asteroids).