How to Freeze a Holobiont: The Great Proterozoic Catastrophe

 

Image created by Dall-E

One of the great features of climate science is that you always learn new things. It is the story of how our planet evolved, changed, and arrived where we are, silly naked apes as we are. One of the most fascinating moments of this long history is the "Snowball Earth" period. Some 700 million years ago, in the Sturtian period, at the end of the Proterozoic Eon, the whole planet got frozen, covered by an ice sheet. Yes, Earth was all white, ice-covered, and nicely frozen. The great holobiont that some call "Gaia" nearly died. It may have survived, barely, because some small areas, maybe volcanic hot springs, remained ice-free.

Why this event? An ongoing research effort is aimed at unraveling the story. The latest results show that the great freezing was preceded by the "Franklin Large Igneous Province" (Franklin LIP). It was another spectacular event but for the opposite reasons. It involved a gigantic volcanic eruption that spread molten lava over a huge region that went from the regions now called Alaska and Greenland. It lasted about one million years. Earth's history is never boring!

Now, some recent data show that the Franklin LIP took place immediately before the great Snowball Glaciation. And the proposal is that the LIP caused the snowball. 

Great, but one moment. There have been several Large Igneous Provinces, LIPs, in the later history of Earth. In most cases, the result was warming, not cooling. The "great dying" of the end of the Permian, about 250 million years ago (at the "Permian-Triassic" boundary) was caused by a giant LIP in the region called Siberia today. The demise of the dinosaurs (apart from birds) was caused by another huge LIP taking place in the Deccan region in what is now India (an asteroid may have helped, but the LIP was probably the main cause). Smaller LIPs also caused havoc in the ecosystem. 

The basic idea is that these huge eruptions inject large amounts of CO2 into the atmosphere, generating a rapid and catastrophic warming that, in turn, causes a dieoff in the ecosystem. So, what did the Franklin LIP have that is different from the more recent LIPs? Is this a new demonstration that climate science is all wrong, actually a hoax created by the appliance industry to force us to cook on induction stoves?

Well, no. If you know the basic mechanisms that control CO2 concentrations and consequently Earth's temperature, the story makes plenty of sense. The Franklin LIP was not different (not so much, at least) from the later LIPs. But the world in which these eruptions took place was completely different. 

Let's start from the beginning: How do LIPs emit CO2? It is because the volcanic lava contains carbonates, compounds that can decompose, producing CO2 and oxides. As for all chemical reactions, the equilibrium between CO2 release and uptake depends on temperature. At the high temperatures of molten lava, carbonates tend to decompose, but, when the lava cools down, the reverse reaction occurs. Now, CO2 reacts with silicates to form carbonates. If the mass of lava is truly huge, as it was in the Franklin LIP, then it is no surprise that the CO2 drawdown is massive. If the temperature is hot enough, but not too hot, the drawdown is also rapid, at least on the geological time scale. Starved of CO2, the atmosphere doesn't act any longer as a blanket to keep the Earth warm. Bang! It is snowball Earth. 

Now, there comes the fundamental point: at the time of the Franklin LIP, the interplay between CO2 release and uptake took place in a relatively simple world: There was no life on land; it only appeared a couple of hundred million years later. So, since the LIP took place mainly on land, it didn't interact with the land biosphere. Then, fast forward 400 million years in the future, and you are now seeing the huge, gigantic, enormous, appalling lava landscape that we call the Siberian LIP. Same thing as before, but with a profound difference. By then, life had spread on land and had plenty of time to create huge reservoirs of carbon that resulted from the decomposition of living matter. This carbon we call "coal." In addition, there were also reservoirs of kerogen (solid hydrocarbons dispersed in the soil) and those hydrocarbons that the naked apes living today on Earth call "fossil fuels." 

Imagine the lava spewing out from the Siberian LIP going through this mass of fossil carbon, and you see that there was a factor that didn't exist with the Franklin LIP: coal was burned by the hot lava and turned into CO2. The same thing happened some 190 million years later with the Deccan LIP. Huge amounts of carbon were turned into CO2 and the resulting warming wrecked the whole ecosystem. Bang! Another mass extinction (the poor dinosaurs were boiled alive). That was the rule with all the Phanerozoic LIPs; their correlation with mass extinctions is reasonably well established, although the details can be complicated. You can find more information in this paper by Ernst and Youbi.

And there we stand: the story of life on Earth is an incredible adventure that sees the geosphere, the atmosphere, and the biosphere interacting with each other, usually resulting in a certain degree of stability but sometimes leading to great upheavals. It is what's happening now, with a large tribe of naked monkeys having taken control of the biosphere and playing the role of a Large Igneous Province by burning the huge reserves of fossil hydrocarbons built over the Phanerozoic Eon. For sure, this new "artificial LIP" will not lead to cooling but to warming. A huge and rapid warming. Gaia will probably survive it, but the monkeys... well, it all to be seen

A simple discussion of the recent results on the Franklin LIP  can be found on Anton Petrov's blog.

How Gaia survived Snowball Earth is described in this post by Ugo Bardi https://theproudholobionts.blogspot.com/2022/12/how-gaia-saved-earth-from-cold-death.html

The paper on the Franklin LIP by Dufour et al. that stimulated this post can be found at https://www.sciencedirect.com/science/article/pii/S0012821X23002728

The link to the paper by Ernst and Youbi on mass extinctions is: https://www.sciencedirect.com/science/article/pii/S0031018217302857

If you cannot access these papers, ask me for a copy

Those Pesky Savanna Monkeys: The New Large Igneous Province

 

This is the second part of a short series dedicated to the "Savanna Monkeys," aka "homo sapiens". In the previous post, I described how they evolved and how they changed Earth's ecosystem in the process. Here, we take a peek at the future. The monkeys could really do a lot of damage. 

The giant volcanic eruptions called LIPs tend to appear on our planet at intervals of the order of tens or hundreds of million years. They are huge events that cause the melting of the surface of entire continents. The results are devastating: of course, everything organic on the path of the growing lava mass is destroyed and sterilized, but the planet-wide effect of the eruption is even more destructive. LIPs are believed to warm coal beds at sufficiently high temperatures that they catch fire. These enormous fires draw down oxygen from the atmosphere, turning it into CO2. The result is an intense global warming, accompanied by anoxia. In the case of the largest of these events, the End-Permian extinction of some 250 million years ago, the whole biosphere seriously risked being sterilized. Fortunately, it recovered and we are still here, but it was a close call. 

LIPs are believed to be the result of internal movements of the Earth's core. For some reason, giant lava plumes tend to develop and move toward the surface. It is the same mechanism that generates volcanoes, just on a much larger scale. From what we know, LIPs are unpredictable, although they may be correlated to a "blanketing effect" generated by the dance of the continents on Earth's surface. When the continents are clustered together, they tend to warm the mantle below, and that may be the origin of the plume that creates the LIP

Of course, if a LIP were to take place nowadays, the results would be a little catastrophic -- possibly more catastrophic than the fantasy of Hollywood's movie makers can imagine. They have thrown all sorts of disasters at hapless humans, from tsunamis to entire asteroids. But imagine the whole North American continent becoming a red-hot lava basin, well, that's truly catastrophic!

Fortunately, LIPs are slow geological processes and even if there is one more of these events in our future, it won't happen on the time scale of human lifetimes. But that doesn't mean that humans, those pesky Savanna Monkeys, can't do their best to create something similar. And, yes, they are engaged in the remarkable feat of creating a LIP-equivalent by burning huge amounts of organic ("fossil") carbon that had sedimented underground over tens or hundreds of millions of years of biological activity. 

It is remarkable how rapid the monkey LIP has been. Geological LIPs typically span millions of years. The monkey LIP went through its cycle over a few hundred years: we see it developing right now. It will be over when the concentration of fossil carbon stored in the crust will become too low to self-sustain the combustion with atmospheric oxygen. Just like all fires, the great fire of fossil carbon will end when it runs out of fuel, probably less than a century from now. Even in such a short time, the concentration of CO2 is likely to reach, and perhaps exceed, levels never seen after the Eocene, some 50 million years ago. It is not impossible that it could reach more than 1000 parts per million. 

There is always the possibility that such a high carbon concentration in the atmosphere will push Earth over the edge of stability and kill Gaia by overheating the planet. But that's not a very interesting scenario: we all die and that's it. So, let's examine the possibility that the biosphere will survive the great carbon pulse generated by the savanna monkeys. What's going to happen?

The savanna monkeys themselves are likely to be the first victims of the CO2 pulse that they generated. Without the fossil fuels they have come to rely on, their numbers are going to decline very rapidly. From the incredible number of 8 billion individuals, that they recently reached, they are going to return to levels typical of their early savanna ancestors: maybe just a few tens of thousands. Quite possibly, they'll go extinct. In any case, they will hardly be able to keep their habit of razing down entire forests. Without monkeys engaged in the cutting business and with high concentrations of CO2, forests are advantaged over savannas, and they are likely to recolonize the land, and we are going to see again a lush, forested planet (arboreal monkeys will probably survive and thrive). Nevertheless, savannas will not disappear. They are part of the ecosystem, and new megaherbivores feeding on them will evolve in a few hundred thousand years. 

Over deep time, the great cycle of warming and cooling may restart after the monkey LIP is over, just as it did for the "natural" geological LIPs. In a few million years, Earth may be seeing a new cooling cycle that will lead again to a Pleistocene-like series of ice ages. At that point, new savanna monkeys may evolve. They may restart their habit of exterminating the megafauna, burning forests and building things in stone. But they won't have the same abundance of fossil fuel that the monkeys called "Homo sapiens" found when they emerged into the savannas. So, their impact on the ecosystem will be smaller, and they won't be able to create a new monkey-LIP. 

And then what? In deep time, the destiny of Earth is determined by the slowly increasing solar irradiation that is going, eventually, to eliminate all the oxygen from the atmosphere and sterilize the biosphere, maybe in less than a billion years from now. So, we may be seeing more cycles of warming and cooling before Earth's ecosystem collapses. At that point, there will be no more forests, no more animals, and only single-celled life may persist. It has to be. Gaia, poor lady, is doing what she can to keep the biosphere alive, but she is not all-powerful. And not immortal, either. 

Nevertheless, the future is always full of surprises, and you should never underestimate how clever and resourceful Gaia is. Think of how she reacted to the CO2 starvation of the past few tens of millions of years. She came up with not just one, but two brand-new photosynthesis mechanisms designed to operate at low CO2 concentrations: the C4 mechanism typical of grasses, and another one called crassulacean acid metabolism (CAM). To say nothing about how the fungal-plant symbiosis in the rhizosphere has been evolving with new tricks and new mechanisms. You can't imagine what the old lady may concoct in her garage together with her Elf scientists (those who also work part-time for Santa Claus). 

Now, what if Gaia invents something even more radical in terms of photosynthesis? One possibility would be for trees to adopt the C4 mechanism and create new forests that would be more resilient against low CO2 concentrations. But we may think of even more radical innovations. How about a light fixation pathway that doesn't just work with less CO2, but that doesn't even need CO2? That would be nearly miraculous but, remarkably, that pathway exists. And it has been developed exactly by those savanna monkeys who have been tinkering with -- and mainly ruining -- the ecosphere. 

The new photosynthetic pathway doesn't even use carbon molecules but does the trick with solid silicon (the monkeys call it "photovoltaics"). It stores solar energy as excited electrons that can be kept for a long time in the form of reduced metals or other chemical species. The creatures using this mechanism don't need carbon dioxide in the atmosphere, don't need water, and they may get along even without oxygen. What the new creatures can do is hard to imagine for us (although we may try). 

In any case, Gaia is a tough lady, and she may survive much longer than we may imagine, even to a sun hot enough to torch the biosphere to cinders. Forests are Gaia's creatures, and she is benevolent and merciful (not always, though), so she may keep them with her for a long, long time. (and, who knows, she may even spare the savanna monkeys from her wrath!). 

We may be savanna monkeys, but we remain awed by the majesty of forests. The image of a fantasy forest from Hayao Miyazaki's movie, "Mononoke no Hime" resonates a lot with us.