Last we left the oxidizing earth in The Weather Outside is Frightful, it had been ravaged by green slimy mutants and then locked in ice and snow from poles to equator. What life existed would have been limited to narrow gaps between blocks of ice in the otherwise frozen ocean, perhaps some photosynthesis could go on under some of the clearer, thinner sections, and the occasional thermal vent or cold seep would have provided some sanctuary for anaerobic microbes just as they do today.
But oxygen is reactive as hell. A billion or so years ago, even at a hypothetical concentration of one per cent, that reaction harbored serious energy. For those organisms which learned to safely tend a biochemical fire deep inside their microscopic bodies, the energy provided by oxygen would act like the supercharger on a funny-car. Eventually, one well known group of creatures would take it even a step further, and turn on the turbo-charger. The funny thing is, many of us here in the US will be enjoying the fruits of that evolutionary development within the week.
The Snowball Earth is a well behaved system. Once the planet reaches that point, simple models conclude it can’t ever get out of it. But surface ice doesn’t change the developments going on deep beneath the planet’s surface or far out in space. Volcanoes still blew, magma still flowed, icy comets still collide. CO2 and other potent greenhouse gases are thus reintroduced into the atmosphere. But on a frozen world with almost no humidity, there was little chemical scrubbing. Earth’s gaseous warm quilt of GHGs could partially be rebuilt and persist. It was just a matter of time really, until they built up enough for one reason or another. Then all hell broke loose.
Once the temperature cleared 32 F at the equator, the feedback loop that locked the world up in ice unwinds with a vengeance. Ice across earth’s midriff began to melt exposing darker water, which absorbed more heat, causing more ice to melt, which exposes more dark water ... Water vapor began building up in the air, trapping more solar heat. Models show this process runs to a terminal end quickly. Perhaps within as little as a century the average global temperature soared, eliminating all or most surface ice.
That kind of change doesn’t happen peacefully. It probably would mean, among other calamitous events, enormous planetary wide cyclonic storms, super-canes and hyper-typhoons that may have lasted years. But for life it meant that all of the sudden, about 650 million years ago, the hardy, surviving microbes that had eked out a living under translucent ice or in thin stretches of open water, some of which were now supercharged with the new oxidizing endo-symbiotic bacteria, suddenly had an entire, warm global ocean, wide open and waiting for them. They went on a fire-breathing evolutionary tear unlike any before.
The mutant green scum spread everywhere blasting O2 into the air and water in heretofore unheard of quantities. The oxygen content of earth’s atmosphere climbed higher. The supercharged oxygen loving microbes drank it in and spread right along with them. The two groups had elegantly evolved to breath each other’s waste gases. And the corrosive gas may have enabled the next major revolution ...
Imagine your PC as it stands before you right now, only take away every bit of plastic. It spills onto your table or desk, a non functioning heap of inner components and dust, held loosely together by fragile wiring. Around Six-hundred million years ago, some single celled critters had begun grouping together in complicated patterns held in place by the biological equivalent of plastic. In the case of the first, tiny, primitive animals, those cells were fixed into a sheets and filaments of a new substance that could be stiffened to an arbitrary degree. It was built in part out of oxygen: Collagen, the superstructure of animal tissue. Without it (And a similar substance for plants called Cellulose) your body, like that of any other metazoan, would collapse into a nonfunctional pile of dust and runny slime spilling all over the floor.
Over half a billion years ago, in warm, shallow Ediacaran Seas, organized multi-cellular life bloomed and then exploded. It was weird stuff. Plants that looked like animals, animals that looked like plants. but by the early Cambrian, some fifty-million years later, more familiar animals appear. They include the direct ancestors of what today we call jellyfish, worms, clams, bugs, and even possibly, people.
Well, to make a very long story short, the newer, multi-celled green plants, evolving insects, and slithering fish-amphibians proceed to forge upstream and onto dry land. Oxygen production really soared now, pushing toward an astonishing 40 per cent, or almost twice as much as we take for granted today. At that concentration, thick mats of biological debris of the newer, tougher, cellulose and collagen equipped plants and animals in the shallow oceans and new dense jungles are practically scorched black in situ, before they’re sealed safely away under oxygen poor layers of dirt and water. Not surprisingly, the richest seams of coal in Europe and the Eastern US date to this time, the Carboniferous Period. By three-hundred million years ago, our own proto-mammalian ancestors had gained a firm upper hold on the oxygen rich world.
But there was an opportunistic newcomer waiting for the time to take them down. Maybe it evolved from a small reptile that colonized the first alpine ecosystems, towering over the low altitude jungles. Or perhaps it swam, and needed an efficient breathing system when it stuck its snout out for a gulp of supercharged air. However it came to be, it was like a sleek purring Ferrari among Model T's.
Two-hundred and fifty million years ago the worst extinction event recorded in the fossil world took place. The Great Dying, the Permian-Triassic Extinction. Roughly 80 percent of all species perished. The temperature soared, oxygen levels plunged so low that some animal lines simply suffocated out of existence. But the new comer, with her special way of breathing, could survive. She came equipped with a turbocharger.
Image Courtesy of Karen Wehrstein
It’s important to understand that this is a highly simplified, and therefore inaccurate, diagram. In reality, the main pipes are hooked up in such a way that it all works through one opening, the mouth. To appreciate that even in schematic takes some pondering and professional explanation. The detailed anatomical reality is exquisitely complicated because there are no ‘air sacs’ above and below the lung. Instead there are hundreds and thousands of tiny air sacs built into the hollow bones. They are divided into two main sets: one that performs the anterior function and one that works opposite in the posterior role.
In this simplified version, air fills one air sac while the other contracts forcing air out through the lungs. Then the expanded air sac repeats the process while the deflated one expands. The net result, the accurate part to understand, is that fresh air is shoved through the lungs on both legs of the cycle. This creature never has to flush stale air out of her lungs. In a world in which oxygen levels have been cut in half, and your competitors possess simple sack-lungs that inflate and deflate, the first proto-dinosaur equipped with this turbocharger had a huge advantage over those panting, out of breath rivals. She and her descendants conquered the land and ruled it for almost 200 million years. Our forebears were relegated to less spectacular eco-niches.
Which brings me to this week: Flying acrobatically like a hummingbird, or long distances at high altitude like geese, takes serious energy. And not unsurprisingly, that same revolutionary dino respiratory pattern is observed in all birds, because birds are dinosaurs (Which surely helped their ancestors take to the air and push out earlier flying reptiles by the middle of the Cretaceous, about 70 million years ago). Even walking birds retained the feature, but because they don’t use their wings for flight, the breast muscle is relatively free of veins, arteries, and the associated blood compared to the darker muscle in the breast of a flying bird.
When you’re cutting though the white-meat of that tender Turkey breast this Thursday, you might notice the chest is large, but the cavity inside is tiny. Lots of muscle, hardly any room for lungs. And turkey’s didn’t need giant versions of mammalian lungs, because they’re raptorial dinosaurs.
So for those of you who will sit down to that turbocharged feast, don't get too cocky about the roles of predator and prey displayed at the table. Birds live long lives, but they can evolve quickly. They descend from animals which survived a massive global warming event that knocked off 80 per cent off all other species, ruled the planet for many millions of years, and then navigated right through the K-T boundary. Today they are the most diverse, successful clade of extant tetrapods as measured by number of species or geographic distribution.
Look into the eyes of a hawk, or an owl, or even a playful sparrow, doesn't it seem like they're patiently planning something? There's a hint of mind behind those sharp eyes. If they could talk, and were aware of their place in natural history, I almost wonder if they'd tell us something like "Keep screwing up the planet you foolish hairless rats: My ancestors used to eat yours, and one day, my descendants will herd your brainless children like cattle."
In the meantime, if you're traveling to a Thanksgiving Feast this week, so long, enjoy your turkey. And don’t forget -- thanks for all the oxygen.