Wednesday, April 9, 2014

The Proterozoic, Part 1

Proterozoic Land

Imagine yourself on a barren world. The atmospheric pressure is high enough to walk around without a space suit, but there are only trace amounts of oxygen, so you'll have to wear a respirator. Oh and, I’d wear a hat too, since the UV radiation is high enough to kill you within hours. Sorry, I should have told you that before you got here. My bad. You might want to put some aloe on that sunburn.

The landscape is bleak, nothing but desert sands and bedrock scoured clean by unrelenting erosion. You see, there are no plants here to firm up the soil. There isn’t any proper soil, for that matter, because there’s nothing alive to make soil. Soil—the kind of soil we’re familiar with—is bound together with organic matter that doesn't exist here.

Yeah, this place is so barren, it doesn’t even have dirt.
Proterozoic regolith

There’s plenty of sand, though. Or, more properly, regolith—the same material that covers the Moon. It sticks to everything, including you. Be careful when you get home and take off your respirator. The fine particles, ground to tiny specks by wind and rain, can damage your lungs if you breath them in.

But one thing this place does have is rain. It must have great torrential downpours, to carve the gullies and channels we'll find in just a few minutes of walking.

Proterozoic cliff

So, have you guessed where we are yet?

If you said Mars, you’re close, but actually we’re in Canada. Toronto, to be specific, but you could go anywhere in Canada and it would look pretty much the same. On the plus side, healthcare is free, but you’ll have to wait a long time to see a specialist. About two and a half billion years, actually, because you're going to have to wait for them to evolve. You see, this is the Toronto of the Proterozoic eon.

There’s no CN tower here, no Hockey Hall of Fame, and certainly no milk in bags. Those things are all in the distant future. There is a waterfront, though, so let’s follow this riverbed and hope it leads us there.

In the riverbed, unlike the open desert we walked through earlier, you might notice some crusty, funny-looking regolith. Check it out:

Desert crust

What the hell is that stuff? Is it alive?

Why yes, in fact, it is. I mean, it’s not exactly alive at this precise moment, but it was alive at one time, and it’ll be alive again just as soon as it rains. What we’re looking at is a terrestrial bacteria mat, and it’s the only living thing on dry land. Really, though, it only comes to life when that dry land is wet. Between rains, it dries out and forms these “desert crusts”1. They resemble lichens, but lichens won’t evolve for another two billion years. Lichens would consider these crusts quite primitive.

Bacterial mats such as these—composed of single-celled blue-green algae—represent the only foothold that Proterozoic life has on land. These pathetic crusts are the pioneers. They’re pushing into harsh, alien terrain, and it's fighting them every step of the way. Bombarded by radiation, starved for water when it’s dry, and poisoned by toxic concentrations of minerals when it’s wet, the odds are stacked against these brave little photosynthesizers.

Desert Crust

So for heaven’s sake, don't step on them. Did you never hear of the butterfly effect, asshole?

Yet, despite the unforgiving environment, these bacteria are holding their own. If you look closely, you’ll find evidence of them all around these riverbeds, on the surface of the regolith and even covering exposed rock faces. Worldwide, they’re prevalent enough that the oxygen they produce is oxidizing minerals right out of the rocks, and those minerals are being washed downstream and altering the chemical make-up of the oceans2. Life on land may not be very impressive in these times, but it’s already changing the face of the planet.

But how did these bacterial mats get here? To answer that question, take off your respirator for a moment and take a whiff. The air is pretty rank, isn’t it? Kind of a mix of fart and rotten egg, eh? I guess I should have warned you about that. You might want to put some aloe up your nose.

That horrible smell is coming from the sea. The bacterial mat stuck to the bottom of your shoe grew from colonizers that blew inland, on the very same winds that carry that awful stench. Most of the bacteria that blow inland will dry up before they even hit the ground, but they remain there in desiccated hibernation until the rains come and wake them up.

But let’s keep moving. As we crest a ridge, we can finally see the beach. It's a colorful sight.

Proterozoic Stromatolites with bacterial mats
 Adapted from an image CC Steve Fareham

This is nothing like the pathetic, barely-there life we met on land. This beach teems with life. These shallow-water bacterial mats constitute the most complex and vibrant ecosystem on Earth right now. The folks in the topmost, green layer, are single-celled cyanobacteria. They have the honor of being the pinnacle of evolution—the most advanced life on the planet.

Yeah, in this eon, the pinnacle of evolution is pond scum. Makes you wonder what they'll think of people in 2.5 Billion A.D. Assuming we don't, you know, destroy the planet and forestall all further advancement of life.

We'll study these funny little organisms (I mean cyanobacteria, not people) in more detail next time. For now, look at the water.

That ain't Lake Ontario out there. If you're thinking it might be the Atlantic, you're wrong again. The Atlantic Ocean doesn’t exist yet, and the great lakes are further still in the future. In fact, the North American continental plate hasn’t even formed. In this time, what will become North America is nothing but a scattered group of archipelagoes in a shallow sea—a sea so ancient, it doesn’t even have a name. But we’re here now, so let’s go ahead and give it one.

We’ll call it Mare Eggfart.

Here in the early Proterozoic Eon, the archipelagos of Mare Eggfart are slowly spreading away from each other, following the breakup of the supercontinent Kenorland. In a few hundred million years, Mare Eggfart will become a proper ocean. But after that, in about seven-hundred million years, the archipelagos will come crashing back in on each other, permanently fusing together to make Laurentia, a continent which will eventually form most of modern North America.

If you want to fast forward a little and watch the continental plates form, you can check that out here. But that's all in the future, which we'll get to in the next installments.


If you just can't wait for next time, check out some other science articles in our handy-dandy Archives.

Citations and References
  1. J. William Schopf and Cornelis Klein. The Proterozoic Biosphere: A Multidisciplinary Study. Press Syndicate of the University of Cambridge. 1992. pg 324
  2. Struken, et al. Contributions to Late Archaean sulphur cycling by life on land. Nature Geoscience 5, 722-725 (2012)

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