The Proterozoic Eon, Part 5

You may remember that we started our journey through the Proterozoic Eon two and a half billion years ago. After a hell of a lot of Monopoly, we now arrive in the still-Proterozoic of only one billion years ago.

We've come more than half of the way home, watching 1.5 billion years of the Earth's history. The continents have shuffled around a lot, volcanoes have come and gone, and we've suffered a couple devastating meteor impacts.

Life has undergone a few major changes, all on the microscopic level. Cyanobacteria destroyed the environment. Complex cells called eukaryotes evolved, then invented sex. At some point along the way, multicellular organisms evolved—we can't say when with any certainty—but they're not much to look at. In fact, from where we're standing along the Toronto coastline, life still looks pretty much like pond scum.

"You guys had a billion and a half years to evolve, and this is the best you can do?"

Adapted from an image Copyright and CC Martyn Gorman

And if life in the oceans isn't looking all that evolved, life on dry land has gotten absolutely nowhere. The coastlines, rivers, and lakes of Earth are teeming with life, but go any distance inland and it's the same sandy regolith we saw when we got here, with nothing but the odd desert crust to prove that life exists.

Now let’s play a couple more games of Monopoly, which will bring us to an even billion years ago. Something funny is happening now. Remember the supercontinent Columbia, which broke up, just like the Eagles?

Well, it’s getting back together, just like the Eagles. The ocean off the coast of Toronto is narrowing. In fact, you can just about see Montevideo coming over the horizon. Wave! All the major plates are smashing into each other, forming the new supercontinent of Rodinia.

Life has been busy, too. Following up on their recent triumph of sex, they’ve now invented murder.

As with sex, it’s entirely possible that murder existed long before now, but it’s here, at about a billion years ago, that we see the first clear signs of it, in the form of predation. We don’t actually have a fossil of a predator eating its prey this early in history. For that matter, we don’t have a fossil of a predator at all.

But we’re pretty sure predators were around, because we can see what their prey were doing to defend against them. Because this is the era when acritarchs, an umbrella classification encompassing microscopic fossils, started to get spiky¹.

Image from PNAS cover July 2005

Other eukaryotes , around this time, also start evolving mineralized coatings that might have been a defense against predators. And stromatolites, those bulbous formations created by bacterial mats, begin to decline, perhaps because they fell victim to newly evolved predators¹.

From: Bengston. Origins and Early Evolution of Predation. The Paleontological Society Papers 8. pp 289-317

We’re going to play a couple more games of Monopoly to take us to about 800 million years ago. Here, the supercontinent Rodinia is breaking up. Yeah, again. You’re going to have to get used to it, because this shit happens a lot.

In the oceans, more crazy shit is going down. The first armored amoeba have shown up², and there’ll be no hemming and hawing this time, because we know these little bastards are predators. There is some hemming and hawing about how long amoeba have been around, though. These little armored dudes are the first to leave fossils, but amoebas may have been around for a while. They may, indeed, have been the predators we saw signs of two hundred million years earlier.

And there’ll be no hemming and hawing about animal life this time, either, because something has just shown up off the coast and no one with a lick of sense would dare deny that it’s an animal. And here it is, in all its glory. The first animal:

From: The first animals: ca. 760-million-year-old sponge-like fossils from Namibia. South African Journal of Science. Vol. 108 no. 1-2 Pretoria 2012.

Yeah, it’s a sponge. They’re animals, you know. It may seem weird, but they are definitely our ancestors, and the ancestors of every worm, fish, lizard, and human being alive today. They’re multicellular, can reproduce sexually, are made of highly specialized and differentiated cell types, have a primitive immune system, and even primitive muscles. They’re animals, and they’re here to stay.

And they’ve shown up just in time for another ice age. Sucks for them.

This ice age won’t last quite as long as the last one—only a couple hundred million years—but it’s going to be even more severe. Again, the glaciers and pack ice will come and go, because an ice age doesn’t mean that it’s always frozen, all the time. But there will be long periods, lasting from 20 to 60 million years, when most of the planet is covered in a kilometer or more of solid ice. Some of these may even have been more “Snowball Earth” events.

I told you to bring a sweater. It’s not my fault you don’t listen.

Two games of Monopoly later, and the planet is finally warming up again. We’re now at about 600 million years ago, the continental plates are coming together yet again, this time to form the supercontinent Pannotia. And, I’m sad to say, we’re only one Monopoly game away from the end of the Proterozoic Eon.

Here at the end, the oceans are warming up and conditions are ripe for life. The cyanobacterial mats are still here, and they still make up most of the biomass on Earth, but eukaryotes aren’t doing too bad.

Larger life (meaning, larger than a microorganism) from this period is hard to classify, because most species are soft-bodied and live on or above the bacterial mats. They don’t leave great fossils, unlike the hard-bodied trilobites and burrowing worms that will start to show up in force a hundred million years from now. But maybe they look something like this:

Image CC Ryan Somma

We don’t know what most of these animals evolved from, and we don’t know what they evolved into, assuming they even left ancestors to evolve into anything. We’re not even sure when they died out. We think it was at the end of the Proterozoic, but without any clear sign of an extinction event such as a meteor or extreme volcanic activity, it’s possible they survived right into the Cambrian. In the Cambrian, the paucity of bacterial mats may have made fossilization of soft-bodied creatures less likely, and so they may have disappeared from the fossil record despite living on.

What we do know is that they’re here in the last days of the Proterozoic, and there are a freaking lot of them. In modern times, you’ll find them in the fossil record all across the planet, if you know what to look for. They spread, they evolved, they covered the planet with an explosion of complex life.

And then they disappeared.

Sorry to say, but so must I. The old Monopoly board has gotten a little decrepit over the past two billion years, and you can hardly tell St. Clare’s Place from Baltic Avenue anymore. We’ve had fun, but it’s time to go. The Cambrian is coming, and we don’t want to get eaten by an anomalocaridid.

***

If you enjoyed this trip through the Proterozoic Eon, check out my other science articles in the Archives!

Citations and References

1. Bengston. Origins and Early Evolution of Predation. The Paleontological Society Papers 8. pp 289-317.
2. Porter. Testate amoeba in the Neoproterozoic Era: evidence from vase-shaped microfossils in the Chuar Group, Grand Canyon. Paleobiology 26 (3) pp. 360-385.

The Proterozoic Eon, Part 4

It's now 2.1 billion years ago, in the Rhyacian Period of the Proterozoic Eon, and the planet is finally thawing out from the 300 million year ice age triggered by those cyanobacterial bastards.

Things are getting back to normal, here in Toronto. I mean, the land is still a barren desert, devoid of life except for those desert crusts we saw earlier, but at least the coasts are regaining a bit of their sparkle. Let’s take a walk along the beach, shall we?

We can see that the algal mats are back, albeit as a cyanobacteria monoculture and not the beautiful, multicolored ecosystems we saw when we first got here. Ah, but what happens when we look at a water droplet under the cartoon microscope?

With the cartoon microscope (which has lower resolution but better clarity than the regular microscope,) we can see that an incredible development has occurred, probably sometime within the past 400 million years. The cell on the right is a prokaryote. These have been around since before we got to the Proterozoic Eon. The cyanobacteria in those algal mats are all prokaryotes.

But the cell on the left is something new. It's a eukaryote, a more complex cell that's larger, with internal structures (called organelles) specialized to particular tasks. You may be tempted to think of them as more evolved than the prokaryotes, but that's your own eukaryotic biases talking. In this time, the eukaryote is nothing but a curious niche organism. Its complexity and size slows down its reproduction cycle, leaving it unable to keep up with the sleeker, more efficiently growing prokaryotes. And all those specialized organelles? No doubt they can be an advantage, but they're also something else that can go wrong. Consequently, these new eukaryotes are more sensitive to heat, cold, and dessication, meaning they can't live in many of the harsh environments that prokaryotes are fine with. So you won't be seeing any eukaryotes colonizing the land, like prokaryotes have. Not for a very long time.

It may seem strange that these, our ancestors, don't hold a special place on planet Earth, but that's just not how evolution works. Evolution isn't striving for complexity. Rather, complexity is more like a byproduct produced as life gropes into unfilled niches.

In the long, long history of life on Earth, complexity has been punished more often than it's been rewarded. Even in modern times, in the golden age of eukaryotes, simple prokaryotic life is far more prevalent than eukaryotes. Prokayrotes may not be as flashy as eukaryotes, but you don't have to go far to find them. Take a close look at your own body, and you'll find a hundred trillion bacteria living in and on it. That's ten times the number of your own eukaryotic cells. So, even inside our own skins, we're still a niche organism.

But these eukaryotes, back here in the Proterozoic? These eukaryotes are gonna make it. They're going to survive—somehow or other—and evolve into even more specialized forms, and their descendants will in turn branch out to become every plant, animal, and fungus on modern-day Earth.

As we place them back into the water—very, very carefully, mind you—we notice strange formations dotting the bacterial mat below the surface. What the hell are those things?

No, they're not the rude artistic endeavors of the cyanobacteria, although that would fit right into the usual habits of those little bastards. These are collections of cells that seem to be forming a sort of multicellular structure. They may be prokaryote or eukaryote. We're not sure, and we can't check, because the cartoon microscope's batteries are dead.

Now, communal living isn't exactly unknown here. The bacterial mats are communities of cells. If not for those pesky eukaryote biases, we might even consider the mats a multicelluar organism. The bacteria in them do exhibit a kind of ad-hoc specialization, exchanging chemical signals and altering their habits to better support the mat. But they can't form the sort of complex structures that eukaryotic cells are uniquely capable of.

But if these formations are made of eukaryotes, and if they're purposefully growing into those complex structure, that would make them the first organized multicellular structures to appear on Earth¹. In the modern era, there's hot debate on the subject. We could have settled the matter right here and now, of course, if you'd only remembered to turn the lamp off on the cartoon microscope.

Nice one.

Well, that's the most interesting thing that’s going to happen around here for a while, so maybe we should get back to that Monopoly tournament.

Okay, after four more games of Monopoly, we've wiled away 400 million years. It's now 1.9 to 1.8 billion years ago and something interesting is finally about to happen. You might want to cover your ears.

You hear that deafening shockwave, and feel that wave of superheated air that’s vaporizing your skin? Yeah, that’s the Sudbury Basin impact event. It’s a meteor that just hit Ontario, making an impact crater over a hundred and fifty miles across. That’s bigger than the crater made by the meteor that will finish off the dinosaurs in a couple billion years. The Sudbury impact rivals even the largest impact in the geological record, which occurred in what will become Africa while we were playing Monopoly. Remember the ash cloud that choked out the sun for a thousand years while you were busy buying up Baltic Avenue? Yeah, that was what that was.

So, yeah. You should definitely put some aloe on that.

This impact occurred so far back that we can't easily estimate the damage it caused to life on Earth, the way we can with later impacts. We don't know how many species it wiped out, and we're not likely to resolve the matter now, since our flesh has been incinerated and our bones buried beneath layers of ash, but I don't think I'm going out on a limb when I say this impact was nasty. It probably killed the majority of organisms on Earth, and caused the extinction of uncountable species.

So, more Monopoly?

Over our next few games, the archipelagos in the Proterozoic sea are going to drift together. The tectonic plate that we’re buried in will run into a bunch of others, and they’ll fuse together along the margins to form one giant plate called Laurentia, or the North American plate. This isn’t just normal continental drift, mind you. Continental plates bounce off each other all the time. This is the formation of a new, much bigger plate, and it will stick together until the modern era. Most of the big continental plates we have today, in fact, will be fusing together from smaller plates within the next few hundred million years. Then all those plates will come together (without permanently fusing) to form a supercontinent called variously Columbia, Nuna, or Hudsonland.

You can watch it all happen here.

But, much like The Eagles, the supercontinent Columbia is going to split up again over our next few games of Monopoly.

Now it’s 1.2 billion years ago, and sex has just been invented.

WELL IT TOOK LONG ENOUGH, DIDN’T IT?

Well, saying sex has just been invented is a little conceited. Bacteria have been having sex for a long time, probably from the very beginning. But they don’t do it the same way we do. They just kind of shoot genes at each other, and if they’re good genes, they tend to stick around. The kind of sex that involves gametes coming together to make a third distinct organism, the kind of sex you’re most likely to regret, is what’s just been invented.

Well, actually there’s a caveat there, too. Because we don’t know if they just now invented it, but this is the earliest we’ve noticed it in the fossil record. And here it is:

Wait, I don’t think that’s right. Here are the actual pictures of the first known evidence of sex:

From: Butterfield. Bangiomorpha pubescens n. gen., n. sp.: implications

for the evolution of sex, multicellularity, and the Mesoproterozoic/

Neoproterozoic radiation of eukaryotes. Paleobiology v. 26 no. 3 p. 386-404.

Wow, that’s hot. I’m surprised we didn’t have to blur those photographs of primordial sex organs.

Sex is a big deal. Without sex, even multicellular organisms can really only clone themselves, budding off little packets of cells to float away and form a genetically identical organism somewhere else. But with sex, you can blend your genes with someone else’s—preferably someone cool. No, really. That really is one of the primary advantages of sexual reproduction: you can pick someone with awesome genes, which will help carry the slack of your crappy genes. And, while these early multicelled eukaryotes couldn’t exactly pick and choose their partners—it was pretty much down to whoever’s gametes happened to float past—they at least got a partner who was a proven survivor.

Are proterozoic lifeforms ready for sex, though? Or will this entire eon turn into one big cautionary tale? We'll find out next time...

***

If you liked this article, check out the other Proterozoic and general science articles at our handy Archives.

Citations and References

1. El Albani, et al. Large Colonial Organisms with Coordinated Growth in Oxygenated Environments 2.1 Gry ago. Nature 466, 100-104 (01 July 2010)

The Proterozoic Eon, Part 3

 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?

The Proterozoic Eon, Part 2

Adapted from an image CC Paul Harrison

When we last left the Proterozoic Eon, it was 2.5 billion years ago and we were finally approaching the shore. It doesn’t look much like a modern beach, does it?

Those rocky protrusions in the tidal zone are stromatolites. They’re a little like coral, in that they're made by microorganisms and grow over centuries. But where corals are complex, multicellular organisms that build calcified structures to protect themselves, these stromatolites are made by simple bacteria—in fact, some of them are the same cyanobacteria that made those terrestrial desert crusts we saw on the way here.

The Proterozoic, Part 1

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.

Don't do it!

My spies have informed me that Toby Harrison, longtime (relatively speaking) friend of the blog, is recklessly encouraging kids to travel through time.

I just want you all to know, so if you find yourself erased from existence, you'll know who to blame.

Let's Not: Time Travel

Let's Not: 

Some Common Mistakes to Avoid
When Traveling Through Time

Maybe the idea came to you in a vision.

Maybe it came when you were reading a physics journal.

Or when you fell off the toilet.

Turning it into reality took decades. While your scientific peers were winning awards, discovering particles, curing diseases... you spent long nights alone in a workshop, in a monomaniacal fugue, focused upon this singular, hopeless dream. They called you a fool. They called you mad. They called you wrong, and that hurt most of all.

They said it was a boondoggle, but now you've proved them wrong. It's finished. It is... a time machine. There it stands, gleaming in the light of a workbench lamp. You itch to step inside and turn it on, to traverse the eons and witness all the wonders of the future and the past.

But wait!

Before you go gallivanting around the Roman Forum in 29BC or visit the Chinese moon base in 2014, let’s spend some time (of which you now have plenty) considering a few common mistakes that people in your situation often make. Remember, those who do not learn from the future are doomed to repeat it.