Book Review/Theory Gloss

(As you know, Gentle Reader, I'm a bit of a nerd, and I love paleontology to death. Here's a review/gloss on a book I read about the Permian Extinction Event).

I just read a very interesting book called Gorgon: Paleontology, Obsession, and the Greatest Catastrophe in Earth’s History by Peter D. Ward (Viking, 2004). It contained a very intriguing theory about the Permian extinction, an event that snuffed out 90% of all life on Earth.

A short exposition: the Permian period was a stretch of time in Earth’s natural history just before the Mesozoic (“Age of Dinosaurs”). There were no dinosaurs during the Permian, only amphibians, lizards, and mammal-like reptiles. If you want to know what a mammal-like reptile looked like, simply take the body of a big lizard and slap on the head of a dog, minus the fur. As far as we know, these therapsids were cold-blooded, laid eggs, and had tiny lizard lungs – a feature important to the extinction theory.

Large carnivorous gorgon, Arctognathus, with therapsid prey

The earth during that time was pretty dry. There was a single supercontinent, Pangaea, with all the landmass on one side of the earth; not a lot of moisture reached the interior. There were a couple of shallow oceans in the middle, but these were quickly disappearing. The dryness made it tough for species to cope, but it wasn’t a deal-breaker – as we know from modern times, thousands of species live quite happily in extremely dry, hot conditions.

 Your friendly neighborhood supercontinent.

Then, according to the theory put forward in Gorgon, two things happened simultaneously: ocean levels dropped, and a vast volcanic region in what is now Siberia began to erupt.

The Siberian Traps were like a giant version of Yellowstone, a one million square mile area of intense volcanic activity continually erupting for a million years. No one is sure whether plate tectonics or deep-earth magma eruptions caused it, but it definitely ruined everyone’s day – billions of tons of poisonous gases, including sulfides and methane, poured into the atmosphere. That much volcanic ash in the atmosphere forms a choking layer that can result in either global cooling (by reflecting the sun’s rays) or global heating (by trapping heat against the earth).

 

Area of Siberian Traps

As if that wasn’t enough, the theory goes, lowering ocean levels exposed vast tracts of seabed. Underwater this sediment is fairly stable, but exposed to the atmosphere it releases methane gas. And with all the tectonic plates forming Pangaea constantly slamming together or ripping apart, the seabeds just kept rising. Billions of trillions of tons of methane poured into the air, enwrapping the planet in a noxious blanket.

Tidal mudflats (not exactly exposed seabed, but similar)

Here’s the upshot: by itself, Methane is a poisonous gas, and contributes to global warming. But it also has this nasty habit of stripping oxygen from the atmosphere and converting into carbon dioxide. So now all that methane from the volcanoes and oceanic muck is now vacuuming up atmospheric oxygen. Which, as you may have guessed, is bad news for the happy oxygen-breathing organisms: amphibians, lizards, mammal-like reptiles, arthropods, mollusks, fish, most bacteria, and many fungi.

Thus, goes the theory, 90% of life on earth, land and sea, asphyxiated – turned blue in the face and died.

Anoxic fishkill, 2012 - a tiny version of the Permian shoreline 250 mya.

“But wait,” you say. “What about plants? They don’t need oxygen. Why would they suffer in a carbon dioxide-rich environment? You’d think they’d flourish.”

Not so fast. Yes, plants like CO₂-rich environments; but they get their nutrients from soil, and viable soil requires decomposition. Much of this decomposition depends on microorganisms, which require oxygen. With decomposition occurring so slowly, and many fungi, bacteria, and other little critters dying off, the nutrients get used up. Sterile soil causes plant death, which leads to wind erosion, which causes larger plants to get blown over, and you essentially have a dust bowl situation. The hot, dry conditions didn’t help, and the climate was getting hotter and dryer due to global warming (caused by those nasty gases). You end up with a cascading chain reaction of death and destruction.

Dust Bowl sandstorm, Texas, 1930s.

“But wait,” you say. “If all the oxygen is gone, wouldn’t life be extinguished? Why did all these organisms still survive?”

Ah, but here’s the elegant part of the theory. I’ll give you a hint: where on earth do organisms survive with less oxygen? The answer: at high altitudes and in the ocean depths.

As the theory goes, those extreme high- and low-altitude organisms, responding to the decrease in oxygen at their own level, begin to descend (or ascend) closer to sea level. Their lungs are huge, allowing them to process oxygen more efficiently. They are also extremely tough, living in cold conditions with extremes of pressure. Adapting to the sea-level pressures over time, they spread out over the earth. Evidence is found in a surviving mammal-like reptile, Lystrosaurus: unlike most of its ilk, it was deep-chested, with big lungs.

Lystrosaurus

Another type of animal also had these strong lungs: Proterosuchians. Related to crocodilians, they were long-limbed, long-necked, and had legs positioned directly under their bodies. They soon gave rise, in the middle Triassic period, to the new rulers of the earth, animals sufficiently adapted to take advantage of this anoxic environment: dinosaurs.

Proterosuchus, showing dinosaur-like adaptations.

For Mr. Ward, the proof of all this is in the pudding – or rather, the fossilized muck. His fieldwork showed a startling stratigraphic phenomenon occurring right at the time of the Permian extinction: before the Triassic, the strata are green. At the Permian/Triassic boundary – and all the way into the middle Jurassic – the strata turn red. Red rock is caused by oxygen bonding to iron, literally rusting it. Since there is always about the same amount of oxygen somewhere on the earth, more oxygen in rock means less in the atmosphere. Only after the middle Jurassic do the rocks return to a more normal color, and this coincides with the Age of Giants, when dinosaurs and marine animals grew enormous, their bodies feasting on oxygen. This also matches up with the rise of birds and the resurgence of mammals – whose lungs were still as inefficient as their reptilian ancestors – as organisms took advantage of the sudden increase in atmospheric oxygen.

Luann Becker (mentioned in this book) pointing to the P/T
boundary: dark Permian rock below, reddish Triassic rock above.

Ain’t science fascinating?

The book itself was interesting in its own right – a sort of adventure story: Mr. Ward spends ten years in South Africa’s Karoo desert, coping with ticks, weather, racial politics, and temperamental colleagues as he studies one of the few places on earth where Permian fossils are abundant. The writing isn’t bad at all, either, although it gets sentimental at times. It wouldn’t have hurt to have a couple of illustrations of the beasts he’s describing: I had to Google dicynodon and gorgonopsid. All in all, a very good book, chock full of fascinating new science stuff, and a great adventure story to boot.