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Chapter 1: How did perceptions of the Cenozoic era shape our understanding of prehistoric climates?
When we think about prehistoric times, especially the age of dinosaurs and before, we usually imagine the Earth as being hot and muggy. Whereas on the other hand, we often view the Cenozoic, or age of mammals, as being the opposite, in the sense that we consider it colder and more dreary.
And this perception has largely been created by the Ice Age, which brought worldwide temperatures down to their lowest points in hundreds of millions of years, potentially. and even when looking at the Cenozoic in general, it does tend to have been colder than previous eras.
However, what is also true is that it is just a myth to believe that the whole thing has been one giant cold spell, when in reality there have been hot periods sprinkled throughout.
And ironically, one of these periods ended up being one of the hottest moments in Earth's history, and an event that turned the world into essentially an oversized microwaved jungle, which shared some resemblance to the bizarre Carboniferous Period, which transpired 300 million years before. And this was the Paleocene-Eocene Thermal Maximum, or PETM for short.
Now, historically, the dinosaur-ending asteroid has often been depicted as having ushered in a nuclear-like winter in permanent colder temperatures. And while it did certainly dampen the temps for a bit, the world did ultimately return to a pretty warm climate just as the Cretaceous had been, with the first stage preceding the Mesozoic having been a relatively warm time for Earth.
In fact, even at that time, there was no permanent polar ice caps on the planet, while carbon dioxide levels were far higher than today. And this heat remained relatively stable for some time, and indirectly eventually led to extensive tropical and subtropical forests developing worldwide, with mangrove, cloud, rain, and swamp forests all becoming fairly abundant.
Though that said, most of the trees you'd see in these ancient forests were the same as each other. In other words, not much diversity, being dominated by just a few species. Meanwhile, animals, on the other hand, were still recovering from the extinction and were in general fairly small.
But they were getting bigger, especially as the Paleocene, the epoch to which the Danian fell under, was coming to a close. And by then, you did see animals that could be half-tonned in weight. So, size was increasing fast. However, this recovery, in somewhat relatively stable climate, was about to be thrown straight into the depths of chaos.
As about 55.8 million years ago, the temperature was suddenly cranked to 100. And I don't mean that things started to slowly get warmer. No, no, no. It was more like one day warm, and the next day you're in an oven. And we see this reflected by graphs that have examined past temperatures. They do a lot of smooth uphill, and then suddenly this giant ugly spike that sticks out like a sore thumb.
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Chapter 2: What was the Paleocene-Eocene Thermal Maximum and why was it significant?
Well, we know this unusual event had something to do with an astronomical increase in carbon dioxide, as the ppm, or parts per million, went up from about 1,000 to over 2,000, which is more than four times the present levels.
And such a massive rise in carbon dioxide isn't just a normal part of the carbon cycle, it clearly indicates that something transpired, something which happened to inject a massive amount of carbon dioxide straight into the atmosphere. Now, we do not know exactly what the culprit behind this event was, but there are a lot of contenders.
Volcanic eruptions, massive underground peat fires, changes in the ocean's circulation, and even comet impacts have also been cited, and more.
I mean, even terrestrial animals themselves have been blamed by some, who believe that an increase in respiration efficiency led to an increased output of carbon dioxide, since that is exhaled when an animal breathes out, and this therefore might have pushed carbon dioxide levels even higher. But again, for now, any agreement on what really happened remains elusive.
What is very clear though, and very agreed upon, is that this heatwave had major impacts on the entire planet and seems to have lasted for about 200,000 years, or about 20 times longer than the last glacial maximum lasted during the Ice Age. And if the latter, i.e. the peak of the Ice Age, caused so many changes in just 7,000 years, imagine how impactful all this heat was.
And so unsurprisingly, virtually every aspect of the planet underwent dramatic shifts. And one thing that also had its own impacts was that the climate not only got hotter, but also much wetter as well, with evaporation rates increasing, especially in the tropics, and rainfall getting way amped up.
This supercharged the already abundant forests, leading to tropical and subtropical forests expanding even further and increasing their range, leading to them growing in places that we don't usually associate warm tropical forests with.
For example, Texas, obviously a much drier area, was at the time covered in tropical rainforests and seasonal tropical vegetation, while in the arctics, palm trees were plenty and even azolla ferns could be found, two flora which today are completely void from these areas.
And so basically, this growth in subtropical and tropical vegetation basically turned the planet into one giant jungle and swamp, as swamps too became far more prominent at this time, especially as sea levels rose and flooding occurred.
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Chapter 3: How did the PETM impact global temperatures and climate conditions?
NDSU heard that correctly. Hoofed. Although truthfully, this group, scientifically known as the Planocranidae, didn't actually have any hooves. Rather, they were equipped with blunt, clawed feet that simply resembled hooves. Yet regardless, this was still a very clear sign that these guys were highly adapted to life on land and, uh, running. Also sporting long, athletic legs.
Of course though, in typical Croc fashion, they also kept what makes Crocs, well, scary. In other words, extensive body armor, and jaws that would, uh, take a nice chunk out of you, making them among the last animals you'd want to encounter.
And though not in the Wasatch Formation, you cannot forget that in this time, if you were traveling the globe, you could have also came into contact with the Stebukids and Mecosuchinae, two additional groups of crocodylomorphs that also had, of course, wicked teeth, and in many cases were even larger than the hoofed crocodiles. Oh, and, uh, these were land crocs, too.
so clearly the lands of earth were teeming with all sorts of life at this time and i guess you could say has had ultimately benefited mammals yet with that said the situation in the water was a bit different it seems that the excessive heat had made things a bit more uncomfortable underwater than above as the petm was a bit of an aquatic extinction event in reality
So much so, in fact, that certain groups like Benthic for Monifera experienced die-offs that was more severe than what they experienced during the KT extinction event. You know, when that giant asteroid slammed into Earth. And it seems that shallow marine ecosystems in particular were devastated by this event, with many of them having simply collapsed under the heat.
Although, it wasn't necessarily the heat itself that was the killer, rather other changes that occurred as a result of this event. And one major change that took place was anoxia, wherein oxygen is depleted from the waters.
You see, elevated seawater temps, water stratification, and oxidized methane released from undersea structures all led to this depletion in oxygen that seems to have affected most oceans and seas, especially the North Atlantic, turning all of them into death traps for many.
Then on top of that, the PETM also seemed to have radically changed the planet's circulation patterns, essentially reversing currents worldwide and transporting warm water to the deeper parts of the ocean, which didn't help either.
And the problems would only continue as the ocean started to experience acidification as well, with the pH dropping about 0.46 units, which is no bueno as it reduces the availability of carbonate ions, which are essential building blocks that marine organisms need to build and maintain their shells and skeletons.
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