ACC, South America, and the Eocene Thermal Maximum: A Thought Experiment

Factual Questions
1

What I hope to do here is to tell a bit of earth history and then look at possible inferences from it that may or may not affect a current debate tppic. It’s in GQ, not GD, because I’m not so much interested in rehashing that debate itself as in seeing if my thinking has anything to bring to bear on it, and because I’m looking for factual error correction on what I have to say. That said, here goes:

It’s the end of the Jurassic. Two pieces of Gondwanaland are ponderously rifting apart a;ong a rift valley that will eventually become the South Atlantic. Already there’s a northward-reaching embayment whose floor will become a narrow ribbon of ocean floor that will, when the solar system is completely on the opposite side of the Galaxy from now and human beings evolve and name the two pieces Africa and South Amerca, be the only ocean floor this old to survive. From the perspective of a hypothetical observer on the African coast, South America is heading west. Farther north, beyond the bulge of West Africa, the lands that will become North America + Greenland and Europe + British Isles are still attached, but the rift is there, beginning to open.

Dinosaurs still rule the Earth, but the days of the great sauropds and carnosaurs are dwindling. Some of each will hold on until the end, but they are oh, so graduallu being replaced by ornithopods and initally-smaller, smarter theropods of other types. During the 40 million years of the Lower Cretaceous, not only do these trends continue, but angiosperms – flowering plants – evolve and diversify greatly, coming to join with the gymnosperms – conifers, cycads, ginkgo and relatives – to dominate Upper Cretaceous flora. Several other ornithischian dinosaurs – nodosaurs, ankylosaurs, ceratopsiqns. pachycephalosaurs, iguanadonts, hadrosaurs – evplve amd diversify. Along with them, though, another group was evolving. For nearly all the Age of Dinosaurs most mammals had been tiny insectivores, more like shrews than anything else now alive. The one major exception since midway through the Jurassic had been the multituberculates, seed and nut eaters including forms much like ground and tree squirrels. Now marsupial and placental mammals became common, though still fairly small in size. (We assume the ancestors of the platypus and echidna were also around, though all fossils are Cenozoic, since they are sp similar to Mesozoic forms and so divergent from other modern mammals.)

Continued next post…

2

The Upper Cretaceous, and indeed the entire Mesozoic Era, came to an abrupt end with the Cjocxulub impact 65 million years ago. It is believed that something, most likely a small asteroid, struck earth at a point off Chicxulub, on the northwest shore of the Yucatan, with a possible secondary impact in Kansas. The effects were drastic. A wide variety of marine life went extinct, including ammonites, several varieties of coral, mosasaurs, ichthyosaurs, plesiosaurs, and a wide variety of lesser forms. Only cold-water plankton seems to have survived.

On land, weird things happened. A shock wave went halfway around the planet. Even the quartz was shocked. In somr places. fire rained from the sky. Acid rain is known to have happened in some places. And it probably brought on a ‘nuclear winter’ pf sp,e duration – how long, we don’t know.

When all was said and done, however, the world was different. The dinosaurs were all gone. Sp were the enantioform birds, the most common of Cretaceous birds. Three of four families of marsupial were extinct, but the survivor continue tp live on and even rxpand its territory today: Didelphidae, the opossums. The multituberculate and several placental families survived. In addition to modern turtles, anogucgektduabs syrvived, as did champsosaurs, crocodile-like aquatic forms. True crocodiles also survived, as did sebecids, land-living predators resembling long-legged short-snouted wolf-like crocodilians.

The world map shows some surprises. North America and northeast Asia were firmly cemented together; dinosaurs had crossed there, and mammals would continue to. A narrower North Atlantic was now open, along with the South Atlantic noted above. But the Old World has some surprises for us. The Tethya Oxean, around since Pangaean times, continued to exist, though not for long. Its western end was dptted with islands that would become Italy, Sicily, Anatolia, etc. But east of this was open water north of an Arabia + <Middle East still firmly attached to Africa – mo Red Sea, and the east ebd of the Mediterranean was open.

Open straight through to southeast Asia. India was an island continent off the east coas of southern Afroca. with the Deccan poised above the Mauritius/Reynion hot spot, which was flooding it with lava. (By India here we mean the Indian subcontinent: Pakistan, India, Bangladesh, and Sri Lanka.)

South America was attached to North America by an isthmus that included the Yucatan, Cuba, and two no-longer-extant blocks of land, and to Abtarctuca by the Cpmp Sur abutting the Palmer/Antarctic Peninsula. Across the Pacific, Aystralia was still llosely attached to Antarctica (Bass and Torres straits not being yet in existence). Hence it would have been possible for an enterprising strain of critter to get from Mongolia via Alaska, Mexico, Chile, Antarctica, and Queensland to westerb New Guinea.

And climates would permit this. South Aneruca and Australia diverted currents north so that currents tended to circulate in the South Atlantic, Spith Pacific, and Circum-Indian Oceans. cool water going north being balanced by warm water carried south across the relevant ocean. The poles tended to be warm.

More…

3

And it got warmer. After the post-K-T nuclear winter, the Paleocene Epoch (65-56 mya) was a time of equable temperatures, when archaic mammals diversified wildly. They were larrgely re[;aced by the earliest representatives of modern lineages in the following Eocene Epoch, which lasted 19 million years (56-37 mya). But during the first seven million years of this epoch, world average temperatures climbed ten full degrees Celsius – 18 degrees Fahrenheit --to what is called the Eocene Thermal Maximum.

Npw to me the interesting thing is that, although that is the sort of global warming most often heard from the Chicken Little school of doomsayers, the results were anything but disastrous: there was widespread afforestation – probably more forested land area existed during the height of the Eocene than ever before or since – very ;ottle desertification, and carbon was flushed by natural mechanisms, notably the afforestation and both natural carbonate deposition and increased shelly fauna in the oceans. Npw I am perfectly well aware of the vast difference in dimension between 50-100 years and 7,000,000 years. And I’m not interested in drawing an invalid parallel, But I am wondering what the time span is for the carbon-fixing mechanisms to catch up woth the CO2 producing ones. And I think that is a valid question to ask.

To finish off my earth history account, what happened? Well, after the Australodelph marsupials had managed to find their way onto that continent, it detached from Amtarctica and moved steadily northeast to its present location. But as Spitj America continued to move west, its extremities connected with two elliptical tectonic plates: the Caribbean in the north and the Scotia (actually the eastern of two small plates that coalesced to form the Scotia) in the south. One can trace their outlines by the island arcs they have thrown up to their east. This turned South America into an island continent with a fascinating fauna of its own, which can be discussed if there is intrest.

But more importantly, it allowed the Circumantarctic Current to form, maintaining a cold-water barrier to insulate Antarctica, which then became a cold reservoir reinforing the current. By 33 mya there was glaciation in Antarctica, and world temperatures had dropped. Though Antarctica did not completely freeze over until 15 ,ya, Paradise was already lost for all intents and purposes. The Pleistocene Ice Age was only the Artic extension of what was already an Antarctic reality.

4

In case nobody else wants to read a long, rambling text with frequent misspellings, the above basically traces evolution from the dinosaurs to the present day, intermingled with descriptions of continental drift. At some point Polycarp mentions that the temperature rose 10 degrees Celsius after the dinos died, and asks how long it takes for “carbon-fixing mechanisms to catch up woth [sic] the CO2 producing ones”

5

[Moderating]

Polycarp, could you please clearly state the questions(s) you wish to ask?

Colibri
General Questions Moderator

6

  1. What factual (as opposed to typographic) errors. assuming there were some, did I make in reporting the earth-history background I laid out?

  2. In particular, is this description accurate?

  1. Presuming the above accurately reports Eocene events, to what extent can this 7-million+year carbon-sink mechanism be relevant to the present concern over ‘global warming’ (ACC) through increased carbon release into the fluid environment om a ca.-200-year span?

My apologies if I rambled and was unclear, and also from the typoes – as noted elsewgere, my eyesight is failing, and I miss stuff I should catch.

7

Pretty much.

This is an active area of research. Some have contended that increased temperatures in the future would jeopardize tropical rainforests. However, research has shown that rainforest floras, including plant families still present today, persisted throughout this thermal maximum.

The question is timing. The temperature increase at the start of the PETM took place over a period of 20,000 years. The episode of global warming currently underway is happening over a much shorter time of decades to centuries. It’s likely that a lot of species won’t be able to adapt that fast.

8

I don’t think it’s a stretch to imagine a post-AGW world eventually repopulated by animals and plants that radiated out to fill niches left empty by the great dying; that’s the normal pattern after mass extinctions.

I think the concern is more personal – that we might not be among those species radiating into the partly-emptied world.

And, not a correction but an amplification, I think you understated the effects of the Chicxulub asteroid impact, or at least took a very conservative approach.

Other sources have been more dramatic, including claims that it set the atmosphere on fire around the world, and that no animal over twenty pounds is known to have survived the impact (the speculation being that the surviving smaller animals were burrowers; the firestorm may have burned to death every animal on the surface of the earth.) It is documented for hurling tektites (molten glass) completely around the earth.

9

Yeah, there’s been some speculation that our timetable for the dinosaur extinction is completely wrong. Where in olden times, we thought that the extinction might have takend place of years, centuries, millenia, or longer–it’s completely possible that it all occurred. . . in a matter of hours. :eek: I don’t know that this is completely accepted, but with the entire surface of the earth ostensibly being incinerated, it would have been a pretty miserable place.