Wednesday, June 11, 2014

The Proterozoic Eon, Part 3

Cyanobacterial Fields Forever
 Adapted from an image Copyright and CC Martyn Gorman

Last time in the Proterozoic Eon, we were playing Monopoly to pass an epoch or ten. And it looks like you've just about bankrupted me. Masterful use of Broadway and Park Place. Now just let me check the time… Yup, like a typical game of Monopoly, that one took a hundred million years.

So now it's 2.4 billion years ago, and we're on the beach in Toronto. Let’s take a look around, shall we?

You may remember that I promised you an environmental catastrophe, but you can be forgiven for not seeing it. Looking around here, it seems that the bacterial mats are thicker and greener than ever. The land is a barren wasteland that looks more like Mars than Earth, but it was like that before the disaster. The only big change is that the sea bed and a lot of the shore has turned a cool shade of red. So where's the catastrophe?

Well, remember how the bacterial mats featured oxygen-producing cyanobacteria on top, and progressively more oxygen-sensitive bacteria below? Well, those cyanobacteria have been dumping their toxic waste—namely, oxygen—into the ocean for all these years.

For a while, it wasn’t a big deal, because the ocean’s a big place, after all. There are chemical processes, too, that soak up and sequester oxygen. But something’s changed recently. We’re not sure what, exactly. Maybe the cyanobacteria have been deregulated, and are dumping more oxygen than the ocean can handle. Or maybe those oxygen-disposing chemical processes have crapped out.

Whatever the reason, oxygen levels in the ocean have spiked. Remember those red deposits?

Proterozoic Iron Beds
Image CC Lebrac

Well, that’s iron. Iron is the precursor to one of those chemical processes that soak up oxygen. Iron gets into the ocean when it's dissolved by rainwater and flows down in rivers and runoff. There, oxygen binds to it, forming iron oxide, which precipitates as rust and settles to the bottom. There, it’s locked safely away.

But just recently, all the goddamn iron—in the oceans and on land—just up and rusted away due to the spike in oxygen levels. That’s why the sea floor has turned red. That iron was the last thing holding the oxygen concentration in check, the ocean's last line of defense against oxygenation. Now it's all gone, and oxygen levels are rising at a terrifying rate1.

You can see the effects already, if you dig up some of that bacterial mat on the shore. Check it out.

Proterozoic Cyanobacterial Mat
Adapted from an image from:

Most of the oxygen-sensitive bacteria have died off, and this once-diverse ecosystem has been reduced to only a few species of mostly cyanobacteria. Of the oxygen-sensitive bacteria who still survive, most are living at the bottom of the ocean, where oxygen concentrations are still low. Even the purple bacteria have suffered a die-off. Purple bacteria are relatively oxygen-tolerant, but they just can’t thrive in these oxygen-saturated waters, and are being out-competed by cyanobacteria.

The most complex ecosystem on Earth has been virtually wiped out, to be replaced by this cyanobacterial monoculture. It’s an algal bloom on a planetary scale.

Oh and, you notice that nip in the air? It’s not your imagination. It really has gotten colder—not just here in Toronto, but over the entire planet. You see, the sun isn’t as bright back here as it will be in the future. Up until now, that hasn’t been a problem, because there’s been plenty of methane in the atmosphere. Methane is an extremely potent greenhouse gas, and for hundreds of millions of years, its greenhouse effect has wrapped the Earth up like a warm blanket. But now the oxygen from the oceans is bleeding into the atmosphere and destroying that methane, converting it to carbon dioxide—still a greenhouse gas, but a less potent one2. What does all that mean? It means the Earth is headed for a punishing ice age.

The only consolation is that, with all that oxygen, Earth is finally gaining an ozone layer3. So you can take off your hat, if you want to. The UV radiation has dropped to a safer level.

Oh God. Your hair is terrible. Put the hat back on. Okay, that’s better.

About that ice age, though. Here in Toronto, we’re in tropical latitudes at this point in the Proterozoic, so we’re going to be the last place to get hit. Let’s play another game of Monopoly to see how it plays out.

You, uh, might want to put on a sweater.

Monopoly Board
A few thousand years later...

Okay, Baltic Avenue’s mine. You’ve got States Avenue. Oh wait. Look, look out there!

It’s not your imagination. That’s an iceberg floating past these equatorial shores. So what is it doing all the way down here? It floated down from up north, of course, where they’re already socked in with glaciers and sea ice. Let’s play a bit more and see how this develops.

Monopoly Board
Another few thousand years...

Oh, Reading Railroad! I really wanted that one. Oh well, at least I got the Electric Company. Hey, what’s wrong? Don’t you want to play anymore?

Oh, I see. You’re freezing to death. Yeah, that'll happen. You really should have brought some warmer clothes. Here, use the Monopoly board to keep the snow off you. Oh, and you might want to put some aloe on that frostbite.

If you look out to sea, and if your eyeballs haven't frozen solid yet, you’ll get an idea of what’s going on. Pack ice, which in modern times is found only at high latitudes, has spread from the poles, all the way down here to the tropics. At the same time, colossal glaciers—and I mean colossal even by glacier standards—are spreading out across the land masses. It's hard to be sure, but this big freeze may cover the entire planet in a nearly unbroken mass of ice called a “Snowball Earth.” Which is a cute image, until you’re standing on it. From here, it looks like the Ninth Circle of Hell.

The cyanobacterial bastards who caused this environmental catastrophe are still alive, though they’re just barely hanging on, living in the thin layer of liquid water between the ice above and the sea floor below. And I bet the oxygen-sensitive bacteria, huddled around volcanic vents in the deep ocean, are laughing their little bacterial asses off.

Now, this ice age is going to last a while. The glaciers may wax and wane a few times, but it’s going to stay cold for the next three hundred million years. That's fifty-thousand times longer than the entire history of human civilization.

So it’ll take us several games of Monopoly to get through it.

Try not to let the race car freeze to your fingers.


If you liked this article, check out my other science pieces in the handy dandy Archives!

Citations and References
  1. Catling, Canfield, et al. The Atmosphere – History 13.08.3
  2. Catling, Canfield, et al. The Atmosphere – History
  3. Catling, Canfield, et al. The Atmosphere – History

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