Nov 02 2017

The Long Winter That Killed the Dinosaurs

ChixulubThere is still a bit of a debate about what, exactly, was responsible for the extinction of the non-avian dinosaurs and 75% of all species on Earth about 65 million years ago (the K-Pg extinction event). There is no question that a large meteor impacted near Chicxulub crater in the Gulf of Mexico at precisely that time, and was certainly responsible for at least some of the extinction. However, volcanism near the Deccan traps in India was also stressing the environment and may have contributed to some degree to the extinction. The debate is really about the relative contribution of these two factors, plus a potential third factor, marine regression.

As a non-expert enthusiast my reading of the consensus of scientific opinion is that the meteor impact was the main cause, perhaps made a bit worse by the pre-existing stressors which were already causing a minor extinction of their own. But the K-Pg event would not have been a mass extinction without the meteor strike.

Adding to this view is a recent analysis that indicates the impact would have caused a devastating continuous subfreezing “winter” from 3-16 years long, enough to make the Starks shiver (sorry for the gratuitous GOT reference). Scientists have been drilling in the Chicxulub crater to learn more about the specific effects of the impact.

I wrote in May of this year that scientists have discovered that the impact threw up large amount of gypsum (calcium sulfate dihydrate). The sulphur this would have thrown up into the atmosphere would have effectively blocked out the sun, reducing photosynthesis and breaking the food chain. The researchers even speculated that the impact was in the worst possible location, because the shallow seas have a lot of gypsum, which would not have been present on land or in deep ocean.

In addition:

The team’s calculations estimate the quantities ejected upwards at high speed into the upper atmosphere included 325 gigatonnes of sulphur (give or take 130Gt) and perhaps 425Gt of carbon dioxide (plus or minus 160Gt).
The CO2 would eventually have a longer-term warming effect, but the release of so much sulphur, combined with soot and dust, would have had an immediate and very severe cooling effect.

They computer modeled the effect on the climate of this much ejecta and calculated that the Earth would have cooled to subfreezing temperatures for at least 3 years and as long at 16 year. It doesn’t take much imagination to consider the effects on living creatures of such a prolonged freeze.

Except for some large turtles and crocodiles, no tetrapod above 25kg survived the extinction event. There was definitely a size component to which species went extinct, which is why the non-avian dinosaurs were so thoroughly wiped out. This makes sense if the primary problem was the lack of food, which would be cause by the loss of photosynthesis and the long winter. Smaller animals could eek through the event on the scraps that survived, but large animals would not have had enough food to survive.

Nuclear Winter

Some of you may recall that Carl Sagan was vocal in warning the world about the potential for nuclear winter. He argued that a prolonged winter was the likely result of the asteroid impact that killed the dinosaurs, and that a significant nuclear exchange could have the same effect – resulting in a “nuclear winter”.

“Beneath the clouds, virtually all domesticated and wild sources of food would be destroyed,” Sagan says. “Most of the human survivors would starve to death. The extinction of the human species would be a real possibility.”

This was not mere speculation. Sagan and others published a computer simulation of their own, using early climate models, in 1983 in the journal Science. Some even credit Sagan and this argument with calming the cold war. The idea of a nuclear winter potentially wiping out the entire human species was more than even mutually assured destruction. The notion of any significant nuclear exchange became suicide. In other words – it was not possible to “win” a nuclear war. The only possible outcome was extinction (or at least the end of human civilization).

It is interesting that now, 34 years later, the prolonged winter hypothesis is getting such strong support from direct analysis of the crater (which had not even been discovered at the time). It is, in fact, even worse than prior models indicated because of the gypsum/sulphur discovery.

In my mind this also strengthens the argument that the meteor impact was the major cause of the K-Pg extinction.

5 responses so far

5 thoughts on “The Long Winter That Killed the Dinosaurs”

  1. Kabbor says:

    I see what you are saying. So long as there are sufficient nuclear weapons around we’re all at risk of extinction. So by waiting and sending them forward in time, we jeopardize the future of humanity… so we must send them back in time! I’d say 65 million years ought to give them enough time to degrade to ineffectiveness.

  2. BillyJoe7 says:

    SN: “As a non-expert enthusiast my reading of the consensus of scientific opinion…”

    Now why would you rely on “the experts” and “the consensus” when you can pore through all the data for yourself, do all you own reasoning, and come to your own conclusions?

  3. googolplexbyte says:

    So the Nuclear Winter hypothesis is rigorous?

    The Chicxulub impact was in the order of 1000x of the world’s nuclear arsenal equivalent and has specific impact area qualities to its boon and it may have only resulted in a 3 year winter.

    I would expect cities to be absent much potential sulphurous ejecta, and our nuclear arsenal not capable of ejecting much of what’s there.

    Also I’ve heard people saying Nuclear Winter is a myth.

  4. BillyJoe7 says:

    Those people you’ve heard saying that must be right then 😀

    Here is a summary of the criticism:

  5. Kawarthajon says:

    Is it true that there were no other small, non-avian dinos at the time of the extinction? I seem to remember chicken-sized dinos from my son’s dinosaur books. Were they all earlier species that weren’t around at the time of the extinction? I find it hard to believe that there were no other small species around at the time, which increases the mystery about why avian dinos and some other species survived.

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