What Really Killed the Dinosaurs? | Hacker News Reader

What Really Killed the Dinosaurs?

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71 pointstokenadult65 comments

The best theory I heard to date is this -

The moon is getting slowly away from the Earth. If we extrapolate backwards, it's obvious that at some point in dinosaur times it was mere meters away from the Earth surface and that's what kill the dinosaurs - they were knocked off by the moon.

it's obvious that at some point in dinosaur times it was mere meters away from the Earth surface

Is there some particular reason under the Hacker News guidelines

http://ycombinator.com/newsguidelines.html

as interpreted by the Hacker News welcome message

http://ycombinator.com/newswelcome.html

that this is the top comment under this thread?

This prompted me to look up other comments by the same user.

http://news.ycombinator.com/threads?id=abcd_f

AFTER EDIT: Just as an example of what I think is a helpful link to share in a Hacker News thread, here are new journalistic reports, "Mammal ancestry expanded after dinosaurs died off,"

http://www.usatoday.com/story/tech/2013/02/08/mammal-ancesto...

and "Rat-Size Ancestor Said to Link Man and Beast"

http://www.nytimes.com/2013/02/08/science/common-ancestor-of...

about scientific investigation into the most recent common ancestor of placental mammals.

I'm no scientist, but I do think it's interesting that the theory of a massive asteroid destroying the dinosaurs arose in the age of nuclear weapons. The article mentions a newer theory involving climate change, which seems to befit the present day.

Why do you find it interesting that this theory arose in the age of nuclear weapons? The "age of nuclear weapons" has been some 60 years now, a lot of new information has come within these past 60 years. Unless your implying that nuclear weapons somehow lead them to this idea. I would argue that the 110 mile crater would be a bigger influence but that's just me.

What he is saying is that it looks like we are explaining the unknown based on our greatest fears - coming to a conclusion and then finding evidence to support it - rather than by looking at the evidence.

It doesn't mean the conclusion is wrong, just that it is always worth remembering how our ability to analyze data points is always done through a haze of our own experiences.

It also arose in the Space Age, when knowledge of space was increasing dramatically.

It only seems reasonable that theories would find wider applications. Knowledge of climate change has greatly increased in the past couple of decades, and it's not as if there's something that only restricts that knowledge to being applied within a few centuries of the present.

To be fair, knowledge of everything else was also expanding dramatically... And the impact theory only really solidified in the 90s after they found the crater.

It is actually even more closely related to nuclear weapons that the timing tells, one of the main proponents of the impact theory was Luis Alvarez, a physicist who had significant influence on the ignition system of the plutonium bomb dropped on Nagasaki (http://en.wikipedia.org/wiki/Exploding-bridgewire_detonator#...).

(The other one was the geologist Walter Alvarez, his son.)

One thing I've always wondered about is what would remain of anything humanity built in 65 Myrs. If there had been a species of very smart dinosaurs populating the Earth for, say 100kyrs, and having a nuclear-capable civilization for say 200yrs... would we even see it?

I keep toying writing a book around the idea that a spaceship full of dinosaurs returns to Earth, having aged very little (Langevin's paradox), and find the planet populated by the offsprings of these pesky tiny egg eaters. Kind of like Planet of the Apes in reverse.

Oh well, if only I had time to write more than HN comments ;-)

As a "Planet of the Apes" fan myself this sounds like a very cool idea, honestly

There is a Star Trek Voyager episode on the idea of dinosaurs leaving earth. http://en.memory-alpha.org/wiki/Distant_Origin_(episode)

It is one of my favorite Voyager episodes.

Thanks so much for the pointer. Will be looking at it right away!

They were quite powerful given that they had a 65MY head start. I hoped they might have brought them back for a visit to handle the borg/dominion. Geeky enough for ya?

If they were nuclear-capable, we'd probably know about them. Even long after the concrete had crumbled into dust and the steel had rusted into minerals, the isotope makeup of the spent fuel would be unmistakable. See: http://en.wikipedia.org/wiki/Natural_nuclear_fission_reactor for a really interesting story. In Oklo, the reactor was critical 1.7 billion years ago and it's still easily recognizable.

It's easily recognizable as a nuclear reactor. But how do you distinguish a natural reactor from an artificial one?

Furthermore, if we assume an intelligent species, wouldn't they either

1) Try to bury and hide leftover stuff, to the point where it's no longer easily found and/or recognizable?

2) Draw more energy out of it than we currently do, to the point where all that would be left would be Fe or Pb?

Also, I forgot to mention that of course, my intelligent dinosaurs would have to be space faring. And that's where a stronger objection appears (IMO): on the surface of the moon, stuff tends to remain unaltered for a long time.

In isolation it's hard to distinguish. But if you find 30-50 reactors all over the globe that were all critical at the same time and all went silent at the same time, I think you'd have to think very hard about how that happened.

As for 1) current proposals (which continually fail to be implemented) are actually to concentrate the stuff and put it in geologically stable locations (c.f. Yucca Mountain). That would seem to be easier to find.

And 2) isn't really plausible. You can't select out and "convert" isotopes like that. You get the fission products you get, and your choice to get "more" out of them is really about how long you are willing to wait for them to decay.

For (1), we choose well hidden geological location, e.g. stuff that is about a mile deep. My guess is we don't have such an extensive knowledge of geologically stable locations one mile below surface.

For (2), I'd venture to say that this is based on what we know today. But then, nuclear reaction or coherent light or traveling to the moon were not exactly "plausible" in 1900 either.

What we know from physics is that there's still a lot of residual energy that could theoretically be extracted, to the point where these isotopes are naturally radioactive.

So to me, that means we are likely to one day figure out how to harness that residual energy.

It depends on where they bury it. On a scale of millions of years, the landscape can be changed radically. Continents get eroded, tectonic plates collide and get subducted. On mere thousands of years, sea levels rise and fall, rivers change course etc.

For instance, the ancient cities of Ur and Uruk used to be close to the shore of the Red Sea, whereas nowadays the sites are about 200km away (silt deposits built up over millenia). The Aegean sea used to extend into a large gulf into Western Anatolia around the time of Homer's Troy.

Everything humans built won't last more than a few thousands of years and modern buildings just a few decades. Even satellites in orbit will decay and burn up in a similar time.

It would be difficult for any visitor coming to an abandoned Earth a million later to discover anything about our presence.

The Earth's crust recycles itself every so often, so given a large enough timeframe, most of the existing surface will be gone, nuclear accidents or no. I suppose a ocean spills could last longer.

http://en.wikipedia.org/wiki/Crustal_recycling

Leonard Richardson wrote that story and it's hilarious.

http://strangehorizons.com/2009/20090713/dinosaurs-f.shtml

This is very odd. Just today an article was published in Science that reinforces the theory that the Chicxulub impact was responsible (although the system was "under stress" before):

http://www.sciencemag.org/content/339/6120/684

I would like to know why the system was Under Stress.

The article kind of contradicts itself. First saying that the asteroid impact theory is pretty outdated and then not really coming up with anything other than maybe it was asteroid impact and/or volcanic activity and/or changing sea levels.

The impact theory is outdated in that people used to think it was by far the largest cause of the extinction. What the article is saying is that scientists now agree it was far more balanced between impacts, volcanoes, and sea levels. Exactly how much each of those contributed is still debated.

It's still generally considered the root cause.

Consider, it's hard to see how sea level changes could be a cause of such a wide spread extinction event. (~75% or more of all species were wiped out) However, it's possible that an asteroid impact could lead to both volcanic activity AND sea level change. That's not to say sea level change was not a contributing factor, just it's most likely part of the overall cascade caused by the impact.

PS: People have caused a significant die-off in what is almost a geologic instant. (http://en.wikipedia.org/wiki/Category:Extinctions_since_1500) However, while habitat destruction is often blamed for man of those extinctions that's just another name for human intervention.

> it's possible that an asteroid impact could lead to both volcanic activity

It could lead to local seismic activity, sure, but I don't think it'd be enough to cause enough volcanic activity. I may be wrong, though.

I noticed the same problem. Sympathy for contrarian stories is a known tic of Slate magazine. Maybe most concisely illustrated by their "you're doing it wrong" series on cooking standard dishes like pancakes, but see also

  http://www.economist.com/blogs/democracyinamerica/2009/10/contrarianisms_end_1

I think it came from their founding editor, Michael Kinsley, who has a taste for this kind of thinking.

I read an interesting comment on Reddit recently that the higher oxygen content of the atmosphere is what primarily supported massive life forms (and that seemed to be proven at least plausible by a recent experiment where researchers were able to grow larger dragonflies in an oxygen-rich environment).

Given the current descriptions of the environment at the time -- higher volcanism, an asteroid impact, global wildfires -- is it reasonable to conclude that this had a huge impact on the oxygen content of the atmosphere? And, if so, couldn't that have simply led to a tremendous selection pressure on species, where larger animals were constantly oxygen-depleted and smaller, more efficient ones were able to continue thriving? Think about it: a Tyrannosaurus would require an immense amount of oxygen to be able to maintain an active hunting pattern; if the oxygen in the atmosphere were depleted by even just a few percent, it would find things like running nearly impossible, and long-distance travel would require frequent rest breaks. I'm not sure how this half-assed notion would fit into the oceanic species' extinction, but it makes a lot of sense for why so many of the larger species died out over a period of time while the smaller ones survived.

I never understood why small dinosaurs wouldn't have had the same likelihood of survival as small mammals?

Also why didn't dinosaurs living in the sea survive this?

I've always had the suspicion there was something more going on to wipe out an entire animal kingdom at once.

why small dinosaurs wouldn't have had the same likelihood of survival as small mammals?

A good question. Of course one category of small theropod dinosaurs (clade Aves, commonly known as birds) did survive the extinction of the rest of the dinosaurs, as the article points out. It's a greater puzzler to figure out why the sea-going groups of clade Reptilia (NOT dinosaurs), like the mososaurs and plesiosaurs, became extinct. An extinction event that brings an end to life forms both on land and at sea is quite a major extinction event.

http://en.wikipedia.org/wiki/Cretaceous%E2%80%93Paleogene_ex...

"I never understood why small dinosaurs wouldn't have had the same likelihood of survival as small mammals?"

Maybe they did have the same likelihood, as in mathematicl probability, but the specific circumstances just worked out this way. A little like the anthropic principle - if it hadn't, we wouldn't be in the world we observe.

Maybe some proto-rat-creature-mammal-things just lucked out.

The anthropic principle, and this type of stochastic lottery argument, are terribly unsatisfying. They may be right, but then again, they may not. They're eminently unfalsifiable, and shouldn't be given any more credence than a typical appeal to divinity.

I vehemently disagree with it being equivalent to an appeal to divinity. I haven't anywhere said 'this is what happened'.

If you want to say it's equivalent to an answer of 'I don't know', then that's fine.

I'm sure you didn't, but either way the outcome is the same. You throw your hands up in the air and walk away, seemingly content to look no further. The anthropic principle and its ilk are a dead end for investigation, and ultimately useless to invoke.

Who said I was content not to look further?

Does "this is what I guess, as far as I know" imply I don't wish to know any more?

The question is "why didn't some other outcome have the same likelihood?" and the answer was, perhaps it did. We don't know what the most likely outcome of the extinction was, only which one occurred.

Mammals are more adept to adapting to climate change. Reptiles on the other hand have a very hard time dealing with even a few degrees of temperature change from there norm.

Sure, but dinosaurs were closer to birds (and thus also warm blooded, as I understand it).

Birds are not strictly "warm blooded" as mammals are, but yes they are not strictly cold blooded ether. They are able to generate their own body heat to some extent yes, but are still fare more susceptible to climate change then a mammal would be.

I don't know about birds during these "dark" times, but todays birds are pretty resilient to wide change in temperature even on a daily basis. They are capable of generating and circulating fair amount of body heat. Their average temperature is typically much higher than mammals. They are also well insulated, more than humans, apes, dogs, cats...

Its also easier for birds to migrate than for land based creatures.

Except that birds did quite well during the extinction event, all things considered; more so than mammals.

But plenty of reptiles survived just fine. It's as if there were something special about dinosaurs. Could there have been some major virus that wiped them out and left other species untouched?

His question was to why "small dinosaurs" did not have the same chances as mammals.

Large dinosaurs(there were no large mammals, but if there were it would apply the same to them) had different issues then the rest, mainly two different things, food and oxygen.

The first reason food, is the main reason. These large animals required huge amounts of food to survive. As the ecosystems collapsed the available food supplies dropped to almost nothing.

The second reason and the same that animals grew to be so large during this time period is predominantly because the oxygen levels were much much higher then they are now. As the ecosystem collapsed so did the oxygen levels. This is why we do not have larger animals now.

They did, they're called birds. Small mammals just grew into more large animal locations.

I know next to nothing about dinosaurs, so someone correct my ignorance:

Don't we define Dinosaurs, in some sense, as "animals that were alive then and aren't alive now?". Obviously, some of the Dinosaur species were related, but aren't there lots of different families of Dinosaurs which aren't connected? Had the wolves died too, wouldn't they also be considered as just another family of Dinosaur?

(Again, I don't really know if this is how Dinosaurs are defined or not. One argument against is that people talk about "birds" being descended from Dinosaurs).

No, dinosaurs are a distinct kind of animal;

- http://en.wikipedia.org/wiki/Dinosaur - http://en.wikipedia.org/wiki/Archosaur

Animals species that used to be alive are classified "extinct", as opposed to being around today which is "extant".

Wolves wouldn't have died off at this time, large mammals hadn't evolved yet.

No, we define dinosaurs "as the group consisting of Triceratops, Neornithes [modern birds], their most recent common ancestor, and all descendants" (Benton, via http://en.wikipedia.org/wiki/Dinosaur). And to answer the GP: yes, many small dinosaurs did in fact survive until today. You can hear them singing in the big blue room behind your office window in spring and summer.

> Also why didn't dinosaurs living in the sea survive this?

The entire ecosystem of the planet collapsed, lots of things went extinct (including some mammals), the classic "dinosaurs" are just the most famous ones.

Precisely. So many things went extinct that is probably better to ask "why did this group survive?" instead of "why did this group go extinct?".

Dinosaurs are still alive today. Birds are avian dinosaurs. What I like to see are those dinosaur shaped chicken nuggets in the supermarket and thinking about how you're really eating dinosaurs.

This idea was punted around for a long time and gained momentum during the “dinosaur renaissance” of the 1970s. By 1996, paleontologists had begun to find fuzzy, fluffy, feathery dinosaurs that confirmed what had been proposed on skeletal grounds—birds are just an offshoot of the dinosaur family tree.

There is a part of me that wants this to be the result of a mischievous entity watching from on high and thinking "oooh, I should probably hide some bones to match that theory, why didn't I think of it when I put the dinosaurs there in the first place..."

It doesn't even have to that high of an entity - there was the Archaeoraptor scandal: http://en.wikipedia.org/wiki/Archaeoraptor

This is the first I've heard of the Deccan Traps. Interestingly, they're "almost" on the opposite side of the globe from the Chicxulub impact (21'N 90'W to 17'N 77'E).

I wonder if their formation or activity might have been caused by the impact?

The Deccan lava flows started about three million years earlier, see for example http://www.ias.ac.in/jessci/jun2001/1352.pdf

Judging by current-day mammals and comparing them to current-day reptiles and birds which have a lot in common with dinosaurs, mammals may have been smarter and more fit to survive in general, especially to changing conditions.

This sounds like one of those "just-so" evolutionary stories without much evidence to back it up.

Since birds are dinosaurs, I wonder what the evolutionary history is of the big birds like emus and dodos. Did they come from medium-sized dinos?

Looks like that is still very much an open question (from a quick scan of wikipedia) - http://en.wikipedia.org/wiki/Ratite

--edit-- though not dodos, pretty sure they were a type of pigeon... or I could be making that up.

Current bird size has nothing to do with their ancestors really since all birds share a common ancestor, all variance came after they branched off.

That's sort of what I suspected; too bad!

The size doesn't matter :)

All feathered creatures must have been evolved from a single one (that first got that feather-mutation), like Archaeopteryx or something older, but the difference in their sizes may be something that occured later.

Yes, but it's kind of interesting if some big birds had big ancestors running around with the dinosaurs. "Later" could mean "after someone got feathers" but still be before the mass extinction.

I recommend reading Jack Horner's "How to build a Dinosaur", he talks about this sort of thing, namely that you can take an existing flightless bird, give it teeth, a tail, and flip the arms around and you've basically got a dinosaur.

The creepy part is people are actually messing around with chicken genes and can turn on things like "grow teeth" and "grow a tail".

- http://www.ted.com/talks/jack_horner_building_a_dinosaur_fro...

You'd think the guy who was the dinosaur adviser for Jurassic Park would actually learn the lesson from the movie, so if we all get eaten to death by chickens, here's your guy.

Isn't the lesson from the movie that the park would just need better security?

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