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55 million years ago, the world was literally a jungle. It was so warm that plants like the bald cypress and the dawn redwood have been found at Ellesmere Island, right inside the Arctic Circle. Only six million short years later, the global temperature began to drop as, over an estimated duration of 800,000 years, atmospheric levels of carbon dioxide collapsed from 3500 parts per million to only 650. What caused this dramatic decline is not relevant to the question. What IS relevant is the extinction event.

I've been having no luck at all finding out if the Icing of Antarctica 49 million years ago created a minor but still noticeable extinction event, particularly among the bird and mammal species. (For further clarification, I'm NOT talking about Grande Coupure, which took place 34 ma, not 49.)

In an alternate Earth, over that same duration at that same point in time, something created a more extreme transition from hothouse to icehouse, say, Australia being so close to Antarctica at the time that it, too, accumulated ice during the mid-to-late Eocene. The question isn't how that's possible, but... Would an Icing of Antarctica as extreme as this create an extinction of plant and animal species, particularly the birds and mammals?

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  • $\begingroup$ Is this what you are talking about ? en.wikipedia.org/wiki/Azolla_event $\endgroup$ – Ville Niemi Mar 16 at 1:17
  • $\begingroup$ @VilleNiemi Yes, but that does not necessarily answer the question. $\endgroup$ – JohnWDailey Mar 16 at 2:38
  • $\begingroup$ Which is why I didn't wrote an answer. ;) $\endgroup$ – Ville Niemi Mar 16 at 2:54
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    $\begingroup$ The crucial factor is the speed at which the cooling took place. 800K to 2 million years is plenty of time for species to adapt to the changes. Note that cooler temperatures don't mean less biodiversity: consider the number of species - notably megafauna - that existed in the cooler temperatures of the last Ice Age, but went extinct as temperatures rose - and rose far more quickly than they would have dropped in your scenario. $\endgroup$ – jamesqf Mar 16 at 4:54
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    $\begingroup$ I do love myself some icing. $\endgroup$ – A Lambent Eye Mar 26 at 16:09
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I am by no means an expert but I think this is indeed possible, just look at the Huronian glaciation for example.

This ice age led to a mass extinction on Earth.

Of course only microorganisms have lived back then (and mostly died because of oxygen, not necessarily the cold). But since ice isn't the best soil for plants a huge portion of the flora would die and if there are no plants then herbivores would also starve, which then leads to a starvation of carnivores as well which rely on those herbivores (and omnivores as well for both reasons). Probably only marine life and animals like penguins, seals or polar bears would survive because sea life could still thrive in this environment (like they do even today near the poles) as long as there is liquid water.

Whatever causes such an extreme icing would probably also lead into a global ice age, especially since ice has a very high albedo so the incoming sunlight gets reflected a lot better than from water or rock. And if less sunlight gets absorbed the earth gets colder which then accelerates the process. At at least one point in earth's history even the entire earth was covered in ice, the Marinoan glaciation. I'd assume that this would definitely lead into a mass extinction for basically every living organism. (Despite not mentioning a mass extinction in the article, it is listed as an extinction event).

Even if the ice only covers let's say Australia and southern African areas like Madagascar and only kills those plants and animals (which would most probably happen since they aren't made for such cold environments), this would cause a huge loss in diversity, since the majority of plants and animals only live there and nowhere else on the planet.

Madagascar:

98% of its land mammals, 92% of its reptiles, 68% of its plants and 41% of its breeding bird species exist nowhere else on Earth

Western Australia:

(...) is home to one of the most diverse and unique floras in the world, with over 210 vascular plant families, and 50-80% of species being unique to the state in the largest of these families.

As someone in the comments of OP's question pointed out, it would also largely depend on the cooling rate but given the fragility of the ecosystem in Madagascar I don't think this would be a huge factor. Especially since they can't flee from the island. Probably some species would try to escape to the African mainland once the ice has created a bridge but at least plants, cold blooded animals and small birds wouldn't make it. Same with Australia.

Hope this satisfies your question.

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  • $\begingroup$ "Whatever causes such an extreme icing would probably also lead into a global ice age" - don't you think you've got the causality reversed? "Icing" is a symptom of low temperatures, not a cause. $\endgroup$ – WhatRoughBeast Mar 25 at 12:29
  • $\begingroup$ I don't get your point here. You just repeated that "whatever" would cause icing. Icing was never the cause of itself here. $\endgroup$ – Tiwaz Mar 25 at 14:09
  • $\begingroup$ I think the confusion comes from OP's question: they are trying to figure out if the symptom of an ice age could cause the extinction when it's the cause of the ice age that's the problem: cooler temperatures killing off base sources of food at the bottom of the food chain leading to loss of species all the way through the chain. $\endgroup$ – KenLFG Apr 17 at 22:44
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I'm not sure if you are asking about a global extinction event or specifically extinction of Antarctic species. Glaciation of Antarctica would certainly cause extinction of local species by destroying their habitats.

On the larger scale, the Middle Miocene disruption or Middle Miocene climatic transition, a later cooling event involving glaciation of Antarctica, caused a wave of extinctions (though nothing like a "Big Five" mass extinction). This event involved a radical drop in CO2 levels.

So - yes, there will be extinctions if the event is severe/rapid enough.

There are interesting good abstracts/papers linked in the references of this Wikipedia article: https://en.wikipedia.org/wiki/Middle_Miocene_disruption#References

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