
The asteroid impact which led to the extinction of the dinosaurs - dangerman
http://www.3quarksdaily.com/3quarksdaily/2017/08/ten-minutes-difference-that-doomed-the-dinosaurs.html
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ouid
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.

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mannykannot
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?

~~~
mark-r
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.

~~~
UnpossibleJim
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.

~~~
mark-r
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?

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EwanG
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."

~~~
ekianjo
The interesting part is this;

> 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.

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Reason077
The BBC covered this very topic in an interesting documentary recently:

[http://www.bbc.co.uk/news/science-
environment-39922998](http://www.bbc.co.uk/news/science-environment-39922998)

[http://www.bbc.co.uk/programmes/b08r3xhf](http://www.bbc.co.uk/programmes/b08r3xhf)

(It does make me wonder about anthropogenic SO2 emissions, and how much of a
cooling effect these have on our climate!)

~~~
roceasta
>anthropogenic SO2 emissions, and how much of a cooling effect these have on
our climate

Anthropogenic SO2 emission as a fringe strategy for global cooling:

[https://www.technologyreview.com/s/511016/a-cheap-and-
easy-p...](https://www.technologyreview.com/s/511016/a-cheap-and-easy-plan-to-
stop-global-warming/)

------
perseusprime11
"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?

~~~
jandrese
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.

------
jMyles
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.

~~~
ChuckMcM
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.

~~~
neaden
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.

~~~
ChuckMcM
Thank you for your response.

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.

~~~
thaumaturgy
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?"

