At last summer grudgingly gave way to autumn here in Florida. The season changed officially on September 23, but practically it was just a few hours ago that the first crisp Fall night fell on a grateful DarkSyde Manor. To celebrate, I’ve set alight a couple of logs in our neglected and mostly ornamental fire place. Here in the flickering solitude afforded at four in the morning, I’m reminded of the coming Holidays and Winters past: there are few moments more simple and satisfying than basking warm and dry in front of a good, roaring fire, while outside the weather is frightful.
Of all mankind’s many companions in the natural world, the licking flames and welcome warmth provided by fire remains our oldest and most loyal ally. Carl Sagan once observed that fire may seem unearthly, and yet earth is the only planet we know of where it exists. But it wasn’t always so.
Long before the first bird flew through Jurassic skies, well before the earliest lobe-finned fish lumbered out of a Devonian pond, even before a dazzling ensemble of alien looking critters ruled the warm Cambrian seas, there was a very different earth. And even though it was at times and places hotter than a blast furnace on that long gone terrestrial inferno, for billions of years fire could not burn.
Below: Lunar Dawn by Karen Wehrstein
Billions of years ago, our planet was unrecognizable. An achingly beautiful oversized moon hurtled through the night sky, throwing down shafts of piercing lunar light through breaks in thick reddish brown clouds. Then three times closer than now, our moon would have raised catastrophic tides to lash against lifeless rocky beaches scoured by howling winds, on a planet spinning twice as fast as the one we know today.
The poisonous smog hugging the first ocean likely included copious amounts of methane, sulfides, ammonia, and water vapor. One lungful would've been enough to kill you before you hit the ground, if the stench didn't knock you out first. But deep in the global ocean, an unprecedented, global struggle was already underway for control of the Air and Water. A new chemical weapon was waiting in the microscopic wings. It was so corrosive it rendered living molecules into atomic dust. For us today it is the breath of life, for organisms in the Archaean Eon it would be instant death. Oxygen was about to be unleashed by the most humble of creatures. The consequences would throw the planet into the greatest biochemical holocaust known in the natural history of the world. And the catastrophe reaches well into our world today in more ways than anyone could ever imagine, until pieced together by geologists and biologists.
It is a loosely guarded secret in astronomy: the earth should be a frozen wasteland. We do not occupy the mythical sweet spot in the solar system. Not exactly anyway. We’re a little too far out, a tad too cool. By the rights of thermal science, and based on incident sunlight received, our planet should be a perpetual, frigid snowball.
Four and half billion-years ago the earth as we know it congealed after a violent collision with a planetoid the size of Mars. One so massive that some of the leftover ejecta blasted into space collected to make the moon. It’s sobering to consider that a good sized chunk of our planet’s original mantle and crust is now orbiting a quarter million miles above us.
But the violence wasn’t over. Analysis of craters on the moon strongly suggest that the earth was subsequently bombarded several times by objects two or three hundred miles in diameter. Those kinds of impacts don’t leave craters: they boil any existing oceans down to the seafloor and vaporize much of the crust, leaving the planet smothered under an atmosphere of incandescent rock vapor sitting guard over a landscape of roiling lava.
For hundreds of millions of years, between the outgassing from hot vents, a slow moving flood of molten iron raining inward to form a dense core, and short lived isotopes cooking down the periodic table, it was literally hell on earth. But the Hadean Eon eventually came to an end.
The earth cooled enough for water to remain a liquid. By perhaps four billion years ago the torrential rains began, and they probably didn’t stop for a long time. Strangely, life seems to have been present from virtually the beginning. The oldest sedimentary rocks we can find, dating to about 3.8 billion years, show possible signs of chemosynthetic bacteria. The sudden appearance of life on the heels of disasters of such magnitude has led some scientists to speculate that primitive microbes were present in the solar nebula to begin with, or hitched a ride on debris blown off a planetary neighbor. Who knows, we may ultimately be Martians, Venusians, or maybe even interstellar Centurions.
We don’t know a great deal about these early microorganisms. Some may have eaten iron, others gouged on sulfur. But one highly successful class may have produced great quantities of methane as a byproduct. Lucky for us, or rather them. Like a goose down quilt knitted from greenhouse gases and gently draped over the planet, methane, along with carbon dioxide, sulfur, and water vapor kept the precious solar heat in, the planet warm, and the snowball earth at bay. And so it remained for hundreds of millions of years. But nothing lasts forever.
Maybe three billion-years ago or so a revolutionary type of microbe arose. The new guys could cook carbon dioxide and water into sugar using sunlight as an energy source. Exactly where and how cyanobacteria evolved is a topic of intense research and debate in paleobiology. Regardless, it was the start of photosynthesis, the biological engine at the heart of all green plants today, and marks the beginning of the Proterozoic Eon. Photosynthesis produces oxygen, and of course humans happen to think pretty highly of it: if we are deprived of oxygen for even a few minutes we suffer and die. But oxygen is an incredibly reactive substance. For the life forms that preceded these oxygen producing upstarts, it was a catastrophe in every way.
Oxygen seeped out of the new microbes and reacted with everything in the primal ocean. Zillions of tons of dissolved iron in seawater turned into particles of rust, settled out in great mats, and formed red bands of rich strata. For the archaen microbes that predated photosynthesis, it was as if they’d been submerged in a sea of acid.
The dissolved oxygen content in the early oceans soared, and the pioneering methanogens along with almost every living thing withered and burned in situ. A handful of species adapted to coexist with the deadly photosynthetic microbes. Most did not. Organisms that could not tolerate oxidation, which included just about everything alive at the time, either went extinct or were chased into oxygen poor, extreme environments where their descendents remain to this day.
Without the ability to think or plan or so much as move from their spot, cyano bacteria had waged and won an epic, global war against all rivals. Unchallenged, under a blood red sky, great blooms of the emerald scum turned the ocean green and poisoned the water with more and more of the corrosive stuff. There came a point when the oxygen sinks in the ocean could absorb no more, but the photosynthetic organisms kept bubbling out the noxious new gas. There was only one place left for it to go.
Oxygen began leaking into the primeval atmosphere, and that’s when the success of the photosynthetic organisms became so great, they almost killed the planet.
With carbon dioxide dropping, and the earth’s crust cooling, the primary remaining greenhouse gas that kept the earth warm enough for water to remain a liquid was methane. But the methanogens had been savaged, and now the free oxygen reacted with the methane gas itself. As the methane waned, the last warm blanket of greenhouses gases was lifted, and the earth began to cool.
Dots of ice appeared at the poles, first seasonally and then permanently. The white icy edge crept further and further away from its polar genesis, it broke through the Artic and Antarctic circles, then inexorably snuck down, reaching greedily for the equator. A relentless feed back loop developed: ice reflected sunlight, cooling the planet further, causing more ice and snow to form. It snowed and it snowed and it snowed until the last drops of moisture froze out of the bone dry air and settled gently on the pristine white surface; in the blink of a cosmic eye, all of planet earth was buried under hundreds of meters of ice and snow.
Humble bacteria had turned the ocean green with their numbers and painted the sky pastel blue with their breath. Now the planet was bright white, the Snowball Earth had begun, the Oxygen Catastrophe was over, and the weather was horrifyingly frightful. And that’s when things get really interesting. One harsh lesson we can draw from this story so far: climate change is a mass extinction event. Sure, it can be natural, just like an epidemic. That doesn’t gives us free license or good reason to intentionally spread either one.
Maybe we’ll resume there, next week, on Sunday Kos. For now, speaking of Fall, it’s time to set my clocks back and steal Mrs. DS, our two furry grrr-animals, and me an extra hour of Sunday morning snuggle time.
Stop now, and take stock of what the Oxygen Catastrophe has brought to our modern world. You read this on a computer built in part of plastic derived from the metamorphosed corpses of long dead bacteria. In your garage sits a vehicle made of steel, an alloy of carbon fixed by primitive photosynthetic microorganisms, and iron teased out of the ancient deposits formed when their waste gas first met iron solute in a vanished ocean. That car is fueled by a derivative refined out of compressed mats of cyanobacteia that sunk to the bottom of the primeval sea to be slowly transformed by heat, pressure, and time into the energy rich syrup we call oil.
Molecular oxygen combines with food in almost every tissue of your body, and if deprived of it for just a few seconds, your life would ebb away faster than the darkness before dawn. Last but not least, the same vital breath of life once exhaled by mutant solar-powered germs which damn near killed the world, now makes the steaks sizzling on the barbecue grill or the roaring blaze in the hearth possible. And while the weather outside isn’t truly frightful, I lit a fire anyway, because it makes being inside on this first crisp Autumn evening so delightful.