h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Entry: The K-T Boundary Extinction Event - A701722
Author: Frogbit - U175610

Started life as a footnote to Ammonites (also in PR). The details of the extinction event commonly blamed on a meteor.

Hi Frogbit,

Is this what you meant to say?

"It was commonly accepted that the dinosaurs died out because they were cold-blooded, and C O U L D regulate their core temperatures effectively in the new darkness, ..."

Awu.

No. It was COULDN'T - thanks Ausnahmsweise. Have also put in a missing tag.

Great entry, I learned something today.

BUT, let me see if I can summarize what I read correctly:

1 - Dinos died in the KT-boundary era. This boundary (or the currently eras themselves) exists because something climatic happened between them, otherwise people would not correlate eras with layers of earth. Or: Otherwise these layers would not be visible. Additionally: There is evidence for a major bang in that era (Iridium and quartz stuff).

SO: A climate change must be correlated with the extinction of the Dinos (and 70% of the rest too? Is that figure that high?) SO: This climate change could have been caused by: Pollution due to volcanoes or by a impact of a bollide (one l or two 'll's BTW?), or a combination of both.

Is that the synopsis?

What about the theory about an over-crowded planet with just enough food for all dinos and just enough clean air for more sensible species, and then a NOT-SO devastating impact followed by some mild changes in climate, triggering the inevitable.

In other words: Maybe the whole biosphere was at it's limit, and a minor change could have triggered a massive revolution. No really BIG bollides and really big mass eruptions needed to explain this. But then again, hollywood would never make a movie out of this.

Great entry. I learned a lot, and it made me think a lot.

HELL

You're welcome. Proof that I read to the end
Do you have anything to say about the craters near Sudbury, Ontario?
Awu.

Nice entry, Frogbit

Maybe an extra:
I once saw in one of the programs about this, that the Deccan Steps are almost exactly opposit the Chicxulub crater. The shockwaves of the impact should have travelled around the earth and focussed there, creating giant earthquakes and vulcanic activity. In this way, the bollide also created the Deccan Traps.

HELL

"1 - Dinos died in the KT-boundary era. This boundary (or the currently eras themselves) exists because something climatic happened between them, otherwise people would not correlate eras with layers of earth. Or: Otherwise these layers would not be visible. Additionally: There is evidence for a major bang in that era (Iridium and quartz stuff)."

Sort of. There are other great extinction events for which the causes are a mystery. The thing that stands out most about the K-T was that it was the end of the dinosaurs and there's a ruddy great crater of the right age (although there is currently debate as to whether the crater pre-dates the end of the Cretaceous)- the iridium layers are a blessing, because it means that a much more precise date for the impact can be gained. The K-T boundary was familiar to scientists for years before it was was postulated that a meteor could be responsible. So the climate change idea was in place before a suitable engine for the change could be identified.
(I am of course conveniently leaving out the catastrophism wrangle that made meteor impacts a taboo subject for years and years).

"A climate change must be correlated with the extinction of the Dinos (and 70% of the rest too? Is that figure that high?) SO: This climate change could have been caused by: Pollution due to volcanoes or by a impact of a bollide (one l or two 'll's BTW?), or a combination of both."

The dinos died out at the same time as a big change to the environment. There were ranges of volcanic activity. There seems to have been a bolide (single L) impact during this period. The pieces can fit together nicely, but there is much debate on the subject. 70% of all life was wiped out - including *all* of the dinosaurs.


"What about the theory about an over-crowded planet with just enough food for all dinos and just enough clean air for more sensible species, and then a NOT-SO devastating impact followed by some mild changes in climate, triggering the inevitable."

Hhhhm. Well, it's as good as any I suppose. I don't know how you get an over-crowded planet, though. Big Pops tend to get whittled down by disease or predation before they can poison the climate against themselves.

Thanks for your input Hell.


Ausnahmsweise:

"Do you have anything to say about the craters near Sudbury, Ontario?"

No I don't, sounds interesting though. Craters. More than one in a small area would suggest a skipping meteorite.

MARJIN

"I once saw in one of the programs about this, that the Deccan Steps are almost exactly opposit the Chicxulub crater. The shockwaves of the impact should have travelled around the earth and focussed there, creating giant earthquakes and vulcanic activity. In this way, the bolide also created the Deccan Traps."

This is, of course, not entirely impossible.

Thanks all - Frogbit.

Hi, Frogbit!

Just skimming this at the moment, my first impression is that the introduction could include a little more basic information. The first mention of an actual date of 65 million years ago seems to be way down the page, and I think that deserves to appear in the first couple of lines.

I'll give it a more thorough read tomorrow....


Azara

Hi Azara - suggestions taken on board and ammended. A few typos have now disappeared as well.

Really nice entry, Frogbit. I found it interesting and informative.

A couple of questions. How do you pronounce bolides? Does it rhyme with collides. Also how do you pronounce Chicxulub - is is as spelled?

I notice that bolides is spelled firstly with one 'l' and then later with two. In the thread, you've said that one is correct, so the entry needs amending.

A small typo - I think - should 'layed' be spelled 'laid'.

Lastly, there seem to be a lot of paragraphs which are not separated properly. This can be done by putting at the beginning and at the end.

Why thankyou Miss Fish.

I think you may have caught me between updates - I couldn't spot a single 'boll' this time around.

Layed > laid. Cheers.

I deliberately chose breaks so as not to, erm, break the flow of the . Have now changed, as ordered.

Bolides rhyming with collides. Well I guess it depends on how *you* say 'collides' According to Chambers it's pronounced 'bow lides' (from the Greek for missile, appropriately enough). But I can't help thinking of the two words together, hence the multiple ll's.

And Chicxulub being pronounced how it's spelled? I think so, but I've only heard Westerners pronounce it, not locals, so I imagine your guess is as good as mine.

I think you're right, Frogbit! All the 'lls' have vanished.

Thanks for the info on pronounciation. Do you think it's worth a footnote?

I'll put one in tomorow - good idea.
And it's pro*nun*ciation, dahling.
Frogbit

You seem to have read/seen different stuff than me about the dust, or else have missunderstood it.

The stuff I have seen has the dust being stratospheric, and thus clogging the moths isn't a problem.

This is the same process that happened during the mount saint helens volcanic eruption, and there was a measurable drop in planetary temperature for about two years. The amount kicked up by something large enough to cause the chixulub crater would be many times greater.

In fact throughout history there have been volcanic eruptions which have caused this problem. we know this because some of them have been chronicled in history, and the dendrochronology data shows disasterous climates for those years (+ a few).

Given that we have decent data for climatic impact from atmospheric dust, I don't think you should dismiss the effect quite so much.

The current theories on what happened state that this massive climatic worsening would have caused a lot of the "large" palm type plants to die off. Because of the loss of these, the large herbivores would rapidly die of starvation, and soon after that,the large carnivores would go the same way.

at no time would it be necessary for all plantlife to die off, so no problem for the moths. Also some must have survived, otherwise the small mamals would not have had anything to eat.

The effect of the dust on the ocean would be that a reduced level of sunlight would result in a smaller amount of plancton growth, leading to a similar sort of cascade in large ocean life forms as well.

I hope this helps.

keep up the good work.

"The stuff I have seen has the dust being stratospheric, and thus clogging the moths isn't a problem."

That's right. As the entry states, the survival of the moth disproves ground-level clouds of dust.

"This is the same process that happened during the mount saint helens volcanic eruption, and there was a measurable drop in planetary temperature for about two years. The amount kicked up by something large enough to cause the chixulub crater would be many times greater."

The K-T boundary impact event and Deccan traps were amazingly different from what happened during the St.Helens eruption. It's like comparing acne to leprosy. I haven't denied the effects of atmospheric dust - I just haven't played it up into the harbinger of doom it is so often portrayed as. That was the point about the moths. The usual narratives would have you believing it was dark for months and the air was unbreathable. The moths disprove this by remaining alive - as do the flowering plants - no plants, no moths.

"The current theories on what happened state that this massive climatic worsening would have caused a lot of the "large" palm type plants to die off. Because of the loss of these, the large herbivores would rapidly die of starvation, and soon after that,the large carnivores would go the same way."

I don't know where you got your data, but I think you'll find the aurucarias (monkey puzzle type angiosperms) came through fine, as did the cycads. Both grow to impressive sizes, and always have done, according to the fossil evidence. This idea is also rather based on the assumption that big dinosaurs liked to eat big plants. Since coprolites are not entirely helpful when attempting to glean a herbivorous dinosaur's diet, it's quite difficult to tell. There's also poor data on their digestion systems, so again the jury's out. From observation of modern large grazing animals, it has been noticed that they all like grass - elephants and giraffe's included (although they will browse tree-tops as well). Before you say it, I *know* grasses were not around then, but another smaller plant (ferns) would probably have been equally digestable.

"at no time would it be necessary for all plantlife to die off, so no problem for the moths. Also some must have survived, otherwise the small mamals would not have had anything to eat."

Yep, never had a problem with that. Not all the mammals were small though. These weren't harvest-mice waiting in the wings - some Triassic fossils show mammal-type animals the size of a dog.

"The effect of the dust on the ocean would be that a reduced level of sunlight would result in a smaller amount of plancton growth, leading to a similar sort of cascade in large ocean life forms as well."

True again. Although it's still a mystery as to why some died and others didn't. Turtles were fine - plesiousar were not.

What I wanted to get across was that the dinosaurs weren't necessarilly wiped out in one go. There's evidence that the Chicxulub crater is older than the K-T boundary - that it didn't happen like this at all. Geological time is different - the events occuring millions of years ago are hard to get in sequence. Events or fossils can be dated, sometimes, down to as little as a million years. A million years! The dinosaurs could have been long gone 10,000 100,000 or 750,000 years before we got hit by that bolide.


Frogbit.

PS - thanks for forcing me into thinking it through again.

about the "small" mammals, I was refering to things up to about the size of a badger. not many mammals larger than this survived.

about chixulib, I thought this had already been nailed down as being the cause of the k-t boundry, due to the fact that instead of being the usual fine layer like it is everywhere else, in the yucatan paninsula it can be over 1 foot thick.

Also, the stuff that was kicked up was about the worse stuff it could be.

"big dino's need big plants" surely this quiery is a varient of the nessie problem?
In the case of nessie, only the top metre of the loch is capable of producing food, which has to be eaten by stuff higher up the food chain. the problemm then is that there isn't enough food to feed a creature that big in the loch, and nothing registers on the sonar as leaving the loch.

Surely you are trying to say that the huge dino's like the brontosaurus (and other t-rex food) lived off grass?

The story as I understood it was that these big dinosaurs were struggling to live on the boundry between population vs food supply and predation vs population.

It would not take a large reduction in available food supply in such conditions for the population to crash, at which time the preditors would over-feed and would then not have a large enough breeding population left to ensure their food supply, thus causing their population to crash as well.

interestingly, the data from places like http://www4.tpg.com.au/users/tps-seti/crater.html tend to show a correlation between impacts and volcanic eruptions and mass extinctions.

I am not suggesting that only the impact was responsible, but I find it highly unlikely that it can be quite as unimportant as your entry seems to make out.

"about chixulib, I thought this had already been nailed down as being the cause of the k-t boundry, due to the fact that instead of being the usual fine layer like it is everywhere else, in the yucatan paninsula it can be over 1 foot thick."

Yes and no. There is still controversy about the age of the crater.

"Also, the stuff that was kicked up was about the worse stuff it could be."

Again true - but plenty of animals managed to survive.

"Surely you are trying to say that the huge dino's like the brontosaurus (and other t-rex food) lived off grass?"

No - I think I mentioned in the last post that grasses hadn't emerged by then. A lot of the sauropods couldn't lift their necks much more than 5 - 6 foot off the ground - stegasaurus (although not a sauropod) had a low feeding range and, like many others, was still a sizeable dinosaur.

"The story as I understood it was that these big dinosaurs were struggling to live on the boundry between population vs food supply and predation vs population."

This is always the case, no?

"It would not take a large reduction in available food supply in such conditions for the population to crash, at which time the preditors would over-feed and would then not have a large enough breeding population left to ensure their food supply, thus causing their population to crash as well."

Very unlikely scenario. Surely it would be enough for the large herbivours to die off. Predators don't really destroy their own food supply. The predation/prey loop tends to go up and down - humans are about the only animals that can drive a food-source to extinction, but only because they know thay can travel large distances to start again somewhere else.

But the main thing is this - there were plenty of small dinosaurs around as well - smaller than the largest mammal. If it were down to size and unsuitable food sources, where did they go? Keeping in mind they all disappeared at once.
Actually, speaking cladistically, many dinosaurs *did* survive the event - the flying ones.

"interestingly, the data from places like http://www4.tpg.com.au/users/tps-seti/crater.html tend to show a correlation between impacts and volcanic eruptions and mass extinctions."

Thanks - I'll have a look later. I'd be surprised if there wan't a correlation though.


"I am not suggesting that only the impact was responsible, but I find it highly unlikely that it can be quite as unimportant as your entry seems to make out."

I *am* suggesting the impact was responsible, but I am also attempting to point out that nothing about that event is cut and dried. There are still a lot of mysteries involved. Although the Chicxulub crater is about the right time, there's still a massive leeway (massive in human terms) during which the dinosaurs could have died out over hundreds of thousands of years before it entered out Solar System. I am not suggesting this is the case - but the event is set so firm in people's minds that they forget there are still an awful lot of unknowns and the book is far from closed.

Hi, Frogbit!

I've been able to give this a more thorough read, and I'm certalinly happy with it the way it is. I like the way you get it across that the neat flashy solution is not the only possible one.

I noticed a couple of typos:
Abou the moths: 'If there air was choked with dust and soot...' should be 'their'.
'The Deccan Traps are sited..' should be 'cited'.


Azara

Thanks Azara - typos ammended.