That’s superCONTINENT, not supercat. (This Siberian fancy cat, though, is gorgeous! And that woman’s deadpan is worthy of Buster Keaton.)
It’s good to keep cats in mind for a little perspective as we check out the spectacle of massive landmasses smashing together, hanging out as a single unit for a while like it’s no thing, and then breaking apart later with great gushes of lava in the form of large igneous provinces (LIPs). (Condie et al.; Ernst et al., 2008, 2013; Huston et al.; Roberts; Rogers and Santosh; Yale and Carpenter)
The last time all of that geological violence happened was with Pangea, whose fragments we’re living on today. There’s the usual disagreement among researchers about dating, but according to Bradley, Pangea began to come together around 310 Ma (million years ago) and started to break apart about 180 Ma.
This sounds simple enough, but the actual event was rough on life: three of the Big Five mass extinctions happened along the way.
Volcanism and LIP eruptions during Pangea’s assembly are associated with the end-Devonian and end-Permian catastrophes, while the Central Atlantic Magmatic Province (CAMP) eruption that helped to break up Pangea has been linked to the Triassic/Jurassic mass extinction. (Ernst et al., 2021; Keller: Pastor-Galán et al.; Racki)
It’s not all bad news, though.
During Pangea’s time, four-footed former fish walked out of the sea and colonized the land as tetrapods; their descendants invented the amniote egg and, among other things, got the two lineages going that would lead to mammals and dinosaurs. (Waikato)
Hard times can inspire life to find new and better adapted ways.
Supercontinents can be described in other ways, for instance, by their deposits of precious metals, laid down during supercontinent assembly, and economic ores (copper, zinc, etc.) loded up as the giant landmass breaks apart with intense volcanism. (Pastor-Galán et al.; Pehrsson et al.)
But we’re not prospectors.
We’re looking into where cats come from. And cats apparently evolved in Asia some 30 million years ago. (Rothwell; Werdelin et al.)
Asia — have you ever noticed its size?
Is that a supercontinent?
Not just now, it isn’t. Eurasia is more of a “once and future” thing, first put together in Pangea and likely to become the core of a new supercontinent in about 250 million years from now.
Eurasia in the future
First off, what’s all this about continents moving?
The last time anyone looked, they were all solid rock, and the seafloor holding up those muddy abyssal plains is certainly composed of hard basalt.
The land we live on seems eternally fixed until there is an earthquake or eruption to remind us just how active Earth really is.
As you might have heard, the planet’s solid outer crust and uppermost mantle, a/k/a the lithosphere, ride a hot, pliant layer of upper mantle known as the asthenosphere.
Below that and on down to the core 1,800 miles below us, heat and pressure cause various phase changes in a solid planetary mantle that, per Oppenheimer, is still “hot enough that it can flow by a slow process, called creep, in which crystals slip past each other, and atoms and ions diffuse from one place to another. (Ice is a more familiar example of a solid that can flow when it is thick enough, as attested to by glaciers and ice sheets.)”
Most of that mantle heat comes from Earth’s core. Hot as the Sun’s surface, our planet’s core is way out of thermal equilibrium with nearby space, which is close to absolute zero: -273.15° C/-459.67° F. (Barge et al.; Oppenheimer)
Heat obeys the law and flows toward cold, perhaps with help from Jason and Tuzo down at the core-mantle boundary, resulting in mantle convection currents that creep along, carrying heat up to the surface. (Oppenheimer)
On those rare occasions when material near the asthenosphere actually erupts, in places like Iceland where the lithosphere is unusually thin, volcanologists are willing to take risks to sample it!
Earth’s lithosphere is broken up into plates.
Each plate contains seafloor, a continent, or some combination of the two.
The planet hasn’t always looked like this. Its surface is constantly in motion — slow and imperceptible to human senses, perhaps, but measurable with instruments, adding up over time.
Plates are made at mid-ocean spreading centers, get destroyed in subduction zones, and change over geologic time as they jostle nearby plates in complex ways that plate tectonics theory covers.
In terms of building a supercontinent, tectonic plates come together when an ocean basin closes. For instance, there used to be a warm sea called Tethys in between Eurasia and the Africa/Arabia and India/Australia plates.
Then subduction zones formed off Eurasia’s southern coast, and the floor of East Tethys slowly disappeared down these great trenches, as India moved north. The eastern part of the seaway closed completely when the subcontinent finally hit Eurasia some 50 million years ago in a mountain-forming collision that still continues today.
That’s why marine fossils are so common in the Himalayas that they wash down riverbeds, where enterprising locals collect and sell them to tourists.
More on ammonites here. Of note, they didn’t make it past the end-Cretaceous extinction, so they were gone before India crashed into Eurasia.
Africa and Arabia are moving north, too, closing off the last remnants of West Tethys (which now bears such names as the Mediterranean, Aegean, and Tyrrhenian seas). This collision is also raising the Alps and other ranges, and it’s causing the region’s volcanism and intense seismic activity.
One day, the Mediterranean will be gone, just like East Tethys, and Africa/Arabia will be sutured to southern Eurasia, just as India now is.
Eurasia will be even larger than it is now!
Farther east, the Pacific Ocean — which was once Panthalassa, much larger than Tethys and encircling Pangea — has lost some 2,800 miles of width to subduction around its fiery rim. While still the biggest ocean on Earth, the Pacific continues to shrink in size. (Maruyama et al.)
Meanwhile, the other end of the India-Australia plate keeps moving north toward Eurasia, closing off the flow of equatorial waters from the Pacific into the Indian Ocean.
Australia and the many island arcs in between will eventually be sutured onto eastern Eurasia. (Maruyama et al.; Wang et al.)
Bottom line: The next supercontinent is assembling before our eyes! (Maruyama et al.; Nance, Murphy, and Santosh; Rogers and Santosh; Wang et al.)
It’s happening on Earth time, though, not by our clocks, so we don’t notice it.
Certain assumptions about other plate motions, say, those of North and South America, must be made in order to produce videos like this. It may or may not be 100% accurate, but whatever the new supercontinent looks like, hundreds of millions of years from now, there will be no active plate boundaries underneath it. Plate tectonics activity, like subduction, can only happen at its edges. (Pastor-Galán et al.)
Eurasia and Pangea
Pangea is the supercontinent we all know and love (perhaps because it hosted dinosaurs and, too, it’s neat the way South America and Africa fit together like puzzle pieces).
Shades of green represent assorted mountain ranges that formed as cratons, shown in gray, and younger, smaller land fragments collided to build Pangea.
On this and other reconstructions, Eurasia is difficult to see, unlike South America, Africa, and a rather truncated North America.
That’s probably because of what Wang et al. report (link added):
Assembly of Eurasia started … at ca. 250 Ma. This assembly overlaps with the tenure and breakup of Pangea and represents an early assembly phase of the proposed future supercontinent Amasia (Mitchell et al., 2012). Following Siberia’s assimilation into Pangea, accretion along the eastern margin of Siberia of continental blocks and terranes occurred between 200 and 100 Ma (Torsvik et al., 2012; Wan et al., 2019). Much of Eurasia represents the reassembly of rifted fragments of Gondwana since the Devonian.
All those collisions, shown as black lines on the graphic, produced mountain ranges and a high plateau: perfect country for the snow leopards that would evolve there and become apex predators.
The Gondwana that Wang et al. mention is another name for southern Pangea, containing what are now Africa, South America, India, Madagascar, Australia, and Antarctica. (India first hit Eurasia about 50 million years ago.)
Pangea’s northern half — Laurasia — consisted of North America, Greenland, Europe, and northern Asia. As the researchers note, the rest of Eurasia came together along with the supercontinent.
Given the fact that, long after Pangea had split apart, Family Felidae first evolved on northern continents that had once belonged to Laurasia and then stayed there until land bridges and/or H. sapiens carried cats into Africa, South America, and Australia (Gondwana) (Hunt; Werdelin et al.), this quote from Rogers and Santosh is intriguing:
The fully assembled Pangea was divided approximately equally between Laurasia in the north, and Gondwana in the south. These two regions had very different histories before the formation of Pangea and were significantly different within Pangea…Differences between continental blocks in Laurasia and those in Gondwana throughout the Phanerozoic [the last 540 million years…BJD] imply that some process that operated during the formation of Gondwana was fundamentally different from processes that caused assembly of Laurasia.
Biology and geology are two totally different things, of course; nevertheless, I can’t help but wonder if that difference, whatever it was, somehow might have contributed to the evolution of cats.
Most likely, long after the Atlantic Ocean had opened and Pangea had broken up, the first cats stayed on northern continents simply because they couldn’t swim to any piece of land that formerly had been part of Gondwana.
But what other subtle Laurasian differences might have been factors over the course of evolution that ultimately led to cats, particularly in the newer parts of Eurasia that had only become a thing during Pangea’s time?
We’ll probably never know.
Disequilibrium and life
So, Earth’s surface isn’t fixed and eternal after all. Still we do all right for ourselves despite that and other natural changes in our environment.
We can maintain our balance in the face of almost anything, from day-night and seasonal cycles all the way to one-off events (from our point of view) like eruptions and other disasters.
It sometimes isn’t fun, but we do it.
This ability to focus is very helpful for survival, but it obscures a basic fact of Nature — as Barge et al. put it, “…life is in the business of converting external disequilibria to lesser internal disequilibria.”
This doesn’t mean that our bodies do their thing even in crises, such as a tornado or a bear attack. They usually do, and that’s another evolutionary advantage we have in common with many living beings.
The business of life is something much more basic than that.
Earth is out of thermal equilibrium with space, right?
As a result, heat flow can be quite intense at the surface wherever the outer crust is thin, say, at a volcano or on a spreading ridge.
And life is usually there to exploit it.
This probably has been going on at various places on our planet’s ever-changing surface for billions of years, with the creatures starting out as extremophiles (the white coating on rocks in this video) and evolving into more complex forms — here, worms, crabs, and shrimp — as time went on.
- The first one-celled, self-replicating critters on Earth probably started out in a hydrothermal area like that, or perhaps one on land, using the free energy and geochemical buffet it cooks up for their own purposes.
- “Lesser internal disequilibria,” mentioned earlier, includes chemical gradients like this. These gradients, plus the physical structures they require (such as cell membranes), probably first appeared in those ancient “hydrothermal hatcheries.” (Durzynska and Gozdzicka-Jozefiak; Kitadai and Maruyama; Mulkidjanian et al.)
Early forms of life somehow found ways to convert geological materials (like the minerals, eroded off continents, that make up the crab’s shell) into useful biology and to use the physical disequilibrium caused by heat flow to power up (jargon alert, though this free book preview is the simplest version I could find online).
None of them had a PhD (or structural complexity of any sort), but what those one-celled Early Precambrian critters came up with and passed on to other generations worked so well that all cellular life on Earth is still based on it today.
You know what else on this planet is in disequilibrium? Its lithosphere, which is constantly in motion.
As Palin and Santosh put it:
Critically, plate tectonics (i.e. a mobile lid tectonic regime)…an ‘unexpected’ geodynamic state that is thought to require many independent factors to be favorable, such as the presence of surface water…
Unexpected. Try modeling that on your supercomputer!
And what about life? Is that one of the favorable factors for plate tectonics? Or is plate tectonics (and its disequilibrium) a precondition for life?
Specialists in every scientific field from astrogeology to zoology are busy investigating these and related questions.
Life, supercontinents, and plate tectonics
As for us, here’s the cat perspective: thus far in the series, we’ve gotten as far as eukaryotes, but they haven’t evolved into animals (metazoans) yet — they’re not even multicellular!
Those developments, and more, apparently took place off the coasts of a shadowy supercontinent called Columbia/Nuna and, later on, its alter ego Rodinia.
I say “shadowy” because very little is known about supercontinents before Pangea other than that there were some, as shown by geologic evidence, such as some LIPs and the presence of collisional mountain ranges like those associated with Pangea but far older. (Condie and O’Neill; Pastor-Galán et al.; Reddy and Evans; Rogers and Santosh; Yale and Carpenter)
What’s really interesting is this:
- There’s eukaryotic life — the very distant ancestors of plants and animals — still under the dominance of bacteria and extremophiles but passing major milestones.
- There is Columbia/Nuna — possibly the first true supercontinent — and it sort of morphs into another supercontinent, Rodinia.
- At around the same time, modern plate tectonics probably gets going and Earth avoids the “stagnant-lid” fate of such rocky Solar System bodies as Mars, Mercury, and our Moon. Unexpectedly. (Mukherjee et al.; Palin and Santosh)
Was it all a coincidence?
There are so many variables and unknowns involved, and it happened so very long ago, that science may never be able to figure out what exactly happened at this key point for the evolution of both Earth and its life, and what interconnections there were (if any).
But one thing is certain: the 82% of our planet’s history known as the Precambrian was not boring!
Next time: Columbia/Nuna and plate tectonics.
I’m going to let the eukaryotes rest until we get through Rodinia and the two Snowball Earth episodes that occurred during its breakup, and then resume that series, trying to figure out their place in it all. (They did have a place, since the end result for them. at around the Snowball Earth time, included taking a significant ecological role for the first time AND, I think, the arrival of ancestral animals.)
Featured image: Sergei Ginak/Shutterstock
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