In summary, the meteorite collided with a small shallow sea, and vaporized a large volume of sulfur-containing gypsum deposits. The sulfur in the atmosphere interacted with water in the atmosphere and formed sulfuric acid in sufficiently large quantities to cool the earth by about 10C, and make photosynthesis non-viable everywhere on earth for long enough that large herbivorous dinosaurs incapable of hibernation died off entirely.
The survival of any birds at all has puzzled me, as modern birds seem to have very active lifestyles and metabolisms that would not tolerate long-term scarcity (as many Cretaceous birds flew, I am guessing the same applied to them.)
This is also true of small mammals, though many can hibernate. I sometimes wonder if it was winter in one hemisphere, and all the surviving mammals were hibernating.
Some modern birds, such as scrub jays, cache food for the lean season - perhaps that is how their ancestors survived?
Right, the article hints at this at the very end, hypothesizing that those animals that did survive were able to adapt to the conditions of an extended winter better than the larger herbivores and their predators.
Birds for instance can subsist on nuts and insects -- things that might survive a disturbed global climate -- and recover the next year, with some local die-offs.
Large herbivores though have to eat plant matter constantly. They can hardly survive a week without eating, let alone months. Those population die-offs then in turn cause a die-off among any species that depends on hunting those animals.
The article mentions that small animals that could subsist on seeds rather than live plants could have survived. This sounds plausible depending on how long it took for plant life to reestablish.
Don't forget, animals (dinosaurs, but also insects) of this size needed the higher concentrations of oxygen in the atmosphere that was present, pre impact. Even a temporary disturbance in oxygen output of the huge forests and robust plant life (including algaes) would have killed animals of this size much quicker than starvation or temperature change.
That's one thing I haven't read about yet, what happened to those oxygen levels of the distant past? Has anybody tried to estimate oxygen levels over time, especially during the extinction event?
Thanks - I was overlooking that seeds can survive a lot longer than the plants that make them. Also roots and rhizomes can survive the death of their above-ground components. Then there are plants that germinate only in response to fire, plants that undergo mass flowerings, and cyclical insects like cicadas - I imagine any of these things could help small mammals and birds survive.
From the article "But it is only last year that we successfully drilled into the impact site, and only now, for the first time, do we really understand why the impact was so fatal. And if the meteorite had arrived ten minutes earlier, or ten minutes later, it would still no doubt have inflicted devastation, but the dinosaurs would still be here and you wouldn't."
> The drilled cores give us the answer. As I mentioned earlier, they are surprisingly deficient in gypsum, although gypsum is abundant both in the more recent sediments, and in nearby sediments laid down before the impact. So the missing gypsum must have been destroyed by the heat of the impact, sending sulphur dioxide gas up into the atmosphere.5 We already know from studies of volcanic eruptions that over months or years this sulphur dioxide would slowly react in the atmosphere to form a haze of sulphuric acid droplets, scattering sunlight and cooling the Earth. That haze, rather than simply dust, is how the Mt Pinatubo eruption affected climate.
> Extrapolating from Mt Pinatubo and other recent eruptions, and taking into account the enormous volume of gypsum sediments in the impact zone, we can estimate that the haze produced by the Chicxulub impact would have blocked enough sunlight to reduce temperatures worldwide by more than 10oC (18oF), while acid rain would also have contributed to the death of much marine life. On land, trees would have shed leaves and shut down as if for what would turn out to be an unusually long winter. The dinosaurs, hugely diverse and successful as they had been through some 180 million years, had no such way of adapting. The herbivores, and the carnivores that fed on them, perished.
> Where did those ten minutes come from? From the rotation of the Earth. The asteroid is falling towards Earth on a fixed trajectory, but the Earth itself is spinning beneath it, one revolution every 24 hours. This corresponds to around 1,000 miles an hour in the region of interest. So arriving ten minutes earlier or later would have placed the impact some 150 miles further to the East or West. And if this had happened, the asteroid would have missed the shallow gypsum-rich continental shelf, and encountered only the oceans on either side. No gypsum in the impact zone, no sulphuric acid haze, no long deep winter. While things might have been pretty rough for anything living within a couple of thousand miles or so, the rest of the world would hardly have noticed.
"And if the meteorite had arrived ten minutes earlier, or ten minutes later, it would still no doubt have inflicted devastation, but the dinosaurs would still be here and you wouldn't."
What does the author mean by we wouldn't be here? Were there no other animals during the Jurassic age? Won't humans be living just like other animals? Maybe be not as advanced but nevertheless be around hiding etc. What am I missing?
When the dinosaurs are around the small mammals can't break out of their niche and evolve into the forms we see today. The dinosaurs have too much of a head start on them. They were stuck for millions of years as mice and rats, and it wasn't until there was a sudden vacuum in the ecosystem that they were able to evolve into larger animals.
The mammals were more adaptable, but in a stable environment that isn't a big advantage. They can't compete against the highly specialized dinosaurs.
Interestingly enough, you see this effect with genetic algorithms today. They're very prone to getting hung up on local maxima and never finding the best solution.
I find the tone of absolute certainty off-putting.
> The asteroid is falling towards Earth on a fixed trajectory, but the Earth itself is spinning beneath it, one revolution every 24 hours. This corresponds to around 1,000 miles an hour in the region of interest. So arriving ten minutes earlier or later would have placed the impact some 150 miles further to the East or West. And if this had happened, the asteroid would have missed the shallow gypsum-rich continental shelf, and encountered only the oceans on either side. No gypsum in the impact zone, no sulphuric acid haze, no long deep winter. While things might have been pretty rough for anything living within a couple of thousand miles or so, the rest of the world would hardly have noticed.
> ...
> And if the meteorite had arrived ten minutes earlier, or ten minutes later, it would still no doubt have inflicted devastation, but the dinosaurs would still be here and you wouldn't.
While the specific hypothesis about the chemistry of the impact zone is very cool - and drilling and analysis a very compelling project - I think that the credibility of the conclusion is clouded a bit by the idea that the reader is supposed to accept with certainty that the events unfolded exactly as the author describes to within a 10-minute window.
I would be interested to understand the affront you feel.
When I read it I heard the process of elimination that scientists went through ruling out all of the ways it could not have happened, leaving only this explanation which fit the facts.
He also explained the 10 minute notion based on earth rotation and some of the other work that had been done which had tried to explain other aspects of the extinction (like why did all the plant life die off?)
As a result I felt the author had done an acceptable job of explaining why he was so certain. Clearly that didn't work for you and I would like to understand that.
I've heard multiple explanations for what exactly killed the dinosaurs off, and every time the person giving them has been fairly certain and had a good explanation for why. Hearing another explanation is always going to make me skeptical now.
Edit: To give some more details this still doesn't explain why dinosaur specie diversity was going down before the impact, or why no small non-avian dinosaur species survived anywhere in the world when so many mammal, reptile, and avian-dinosaur species did.
I am asking because I am interested in the communication and presentation of scientific results to diverse audiences.
I have observed that the notion of 'current best explanation for the observed results' can be misinterpreted. All science is the process of people trying to find an alternate explanation, other than the one proposed, that fits the evidence and can make predictions about evidence that has yet to be found. It is the totality of the observed facts that the explanation explains, and the ability to accurately predict other facts that will be found assuming the explanation is the one that really explains things.
What I've observed is, as you have described, that during the evolution of the scientific investigation, especially when hypotheses are shown to be incomplete and are updated, that communication is heard as a "different" answer rather than as a more refined answer. As my daughter observed about meteorologists predicting rain, "they don't really know, they are just guessing." And that is true with all science, there is no Arc of Knowledge where we can look up the answers to the questions in the back.
The author of the article clearly felt convinced, based on the evidence presented, that this hypothesis about the events that took place is the most accurate idea we have to date. And they showed how other possible explanations had been explored, how predictions (about Iridium) had been made and validated, how estimates of mass and size were made, how the physics of the impact compared to those on other planetary bodies that don't have erosion, Etc. And that confidence they felt came across as 'certainty'.
And yet, their own confidence and their sharing of how they came to have that confidence is off putting. Which is, I am fairly certain, exactly the opposite of what the author had hoped for. They had hoped to share their understanding so that the reader could be confident in their own belief that this is, to the best of our knowledge, exactly what happened so long ago.
I too am interested in this. I have a grandfather who is otherwise thoughtful and open-minded and exceptionally intelligent, but he finds the asteroid impact theory of extinction completely impossible. Attempting to convince him has been fun in that we have a good relationship and he'll readily respond to me without turning it into a fight. If I can learn what works and what doesn't when changing his mind with available evidence, then that might work with other more difficult people.
In his case, there are a few issues:
1. Related to the other commenter's point, he's not fond of statements of absolute certainty. He likes to say, "well, we weren't there, were we?" I liked the article a lot, but I can see how it was doing really well right up until the very end, where it accelerated into story mode. Everything before that was more carefully written; "we think this because...", "it could have been this other thing, but probably not because...". For people willing to consider evidence that runs contrary to their belief system, a preponderance of evidence coupled with consideration of differing opinions is way more convincing.
2. It stretches the limits of his imagination. On human scales, imagining a global catastrophe like this can be difficult. Media, artist's depictions, CGI and so on don't seem to help much here (caveat: unless they're really, really good). Examples from other parts of the solar system do help a little.
3. He wants all of his questions answered. From that standpoint, this article is excellent. People want puzzles tidied up into nice, neat little arrangements with a bow on top. Why did some things survive and others didn't? If it just got really cold, why did the dinosaurs in the ocean die out? If it was so big, why can't we find the asteroid that did it? Weren't things already dying out anyway? What if the dinosaurs just got so big that they couldn't reproduce anymore? These are all actual questions he's had. It can be a very frustrating dialogue for scientists and the science-interested, where we learn not to expect answers to all questions right away and any answer that begins with "I don't know" is regarded as evidence contrary to the theory, but the more answers that can be provided, the better, even if they're our best guess at this time. So then you have to know your subject matter really, really well, better than the majority of hobbyists do.
4. Constant exposure helps a lot. I think people that become comfortable with lack of certainty also tend to become averse to argument and conflict, and that doesn't help their cause in the long run. You have on the one hand someone who will argue a case from a position of ideological certainty, and on the other hand someone who says "maybe" and "we don't really know" and "at this time we think" a lot. If you know nothing about some given subject, who would you tend to believe? Imagine it's someone presenting arguments for a subject you have tenuous opinions about, but not a lot of expertise or domain knowledge. I think this is why people like NDT and Nye and Dawkins are more popular in the mainstream while being somewhat distasteful among other intellectuals. They present evidence-based views with the same conviction and tonality and theatre as you might expect from a preacher.
That last point runs somewhat contrary to the first, but I think there's a happy medium where I can just send grandpa a really good article, like this one, about once a week or so, and say, "here, this does a good job of answering some of your questions, what others do you have?"
Earlier explanations of the dinosaurs' demise were pretty speculative. Impact and Deccan traps volcanism were the about the only hypotheses that had specific physical evidence to support them.
According to Stephen Jay Gould, it turned out that the claim of declining dinosaur (and ammonite) diversity was exaggerated through poor statistical analysis, failing to account for the fact that a species' last appearance in the record does not mean that it became extinct immediately afterwards. Furthermore, when paleontologists specifically looked into diversity up to the boundary, they found it. Diversity is always changing, so some decline beforehand is not fatal to the theory.
Gould also believed that many geologists resisted the impact hypothesis on the basis of a somewhat dogmatic objection to 'catastrophism' in any form. This kept competing theories alive longer than perhaps they should have.
FWIW, I am not entirely satisfied with the explanations of how some classes (especially birds) survived, but in any case there were not so many survivors; terrestrial vertebrates came fairly close to total extinction. When the odds are long, chance can make a big difference.
Journalists often want a simple story to tell, and the myth of the dispassionate, objective scientist is largely just that: they will present the ideas they favor in the best light that evidence permits, and sometimes beyond. Furthermore, the evidence increases over time, whether for or against a hypothesis. When a hypothesis accumulates more, and more diverse, evidence consistent with it, its plausibility goes up, and if you want an informed opinion (of anything), you have to follow those developments.
> When I read it I heard the process of elimination that scientists went through ruling out all of the ways it could not have happened, leaving only this explanation which fit the facts.
I share the affront, based largely on this very idea.
You're using Sherlock Holmes' catchphrase: "Eliminate the impossible, and whatever remains, however improbable, must be the truth". It's fun fiction, but it's terrible science; you're never going to be able to distinguish between the improbable and the impossible to the degree required, and more importantly, you'll never even be able to enumerate, much less eliminate, every theoretical possibility.
This is the fallacy of accepting the alternative: You conjecture that cold temperatures are caused by the god of the winter wind blowing on the earth. You do a careful statistical analysis demonstrating that it is unlikely that day-to-day temperatures are determined by chance variation (for example, December days are overwhelmingly and predictably colder than July days). So you "logically" accept that you've supported the god-of-the-winter-winds theory. You haven't; rejecting one hypothesis is not evidence in support of any particular other hypothesis.
Thank you for this response. I am really interested in your first sentence.
As I understand your response, I paraphrased a description of the scientific method and you were affronted by it. Is it science in general?
Your last paragraph was especially illustrative for me, while I am not familiar with a "fallacy of accepting the alternative" as I read it, your statement "rejecting one hypothesis is not evidence in support of any particular other hypothesis" does not explain to me the evidence you used to reject one hypothesis over another.
Please correct me if I'm wrong, but it reads like you feel that any hypothesis would be acceptable as an alternate. However that is not true, either in science or in Sherlock Holmes novels. As you probably know, in a Sherlock Holmes story at the end is the big reveal in which all of the facts are put together by the detective so that all of them can be true at the same time. Sometimes he does this by finding an additional clue which binds together two seemingly unrelated bits of evidence. But the great detective would not entertain a theory that the "Easter Bunny did it" in the absence of any possibility that the Easter Bunny could have done it.
In order for an alternative hypothesis to be considered valid by a scientist, it must first explain every fact that we already know to be true. Further, if the alternate needs an entirely new thing that hasn't been discussed before (your "God of Winter" for example), then it also has to have the evidence that was used to establish that new thing. As a scientist you have to accept that your hypothesis and your new thing will be challenged until nobody can find a single fact that would have to be different or a way in which your evidence can not be verified or reproduced. Of course during that process of challenging a lay person might hear one scientist who supports on hypothesis and one who supports a different hypothesis.
But would this be offensive to you? And if so what generates the offense? The lack of an answer or the multitude of answers?
"The asteroid is falling towards Earth on a fixed trajectory, but the Earth itself is spinning beneath it, one revolution every 24 hours. This corresponds to around 1,000 miles an hour in the region of interest. So arriving ten minutes earlier or later would have placed the impact some 150 miles further to the East or West."
If the asteroid had arrived 10 minutes later on the same trajectory, the Earth would have moved about 18,000 km through space and it would have missed us entirely!
It's unlikely that the asteroid would have come so close (18,000 km is closer than GPS satellites) without being pulled to Earth because of the planet's gravitational field.
At 40,000 MPH (or about 18 kM/s) at best, the Earth could deflect it somewhat from 18,000 miles out. Remember that escape velocity is only 11 kM/s, so even if the asteroid grazed the atmosphere if it didn't slow by more than 7 km/S it would have just shot back out into space.
The GP is correct, if the asteroid is on an orbit that is outside of the ecliptic plane.
But to the article author's point, had it landed on nothing but ocean it would have had a different outcome. I believe the +/- 10 minutes conceptually was a way of illustrating some of the things that would have changed the outcome.
I agree with your skepticism of the author's conclusion. For example, we only know that the location/timing of the asteroid impact was so devastating because it did in fact hit there and so we were able to study it and find the "smoking gun", in other words, it wasn't obvious. But how can you assume that if it hit somewhere else at some other time that we wouldn't have found some hidden life-ending mechanism in that event as well?
