Composing Earth's Symphony: A New Perspective on the Carbon Cycle

Join me as I unravel the intriguing story of our latest research, uncovering the hidden role life has been playing in shaping the climate of our planet. We'll explore complex processes, challenge long-held beliefs, and embark on a journey of discovery. This is about the future of our home, our impact on it, and the audacious idea of reshaping Earth to create a vibrant future. Ready to dive in? Get yourself a cup of coffee or tea ;)

TLDR: In our latest Nature paper, we've discovered a twist in our perspective on Earth's geological carbon cycle: we discovered that the weathering of organic carbon in rocks can release CO2, indicating that the Earth's carbon cycle, or "thermostat," is not primarily inorganic, but significantly organic. This finding suggests that life itself has played a more substantial role in maintaining Earth's climate through deep time than we previously understood. Whilst this is hopeful, this doesn't mean everything will be fine. Life has also caused major climate shake-ups. Looking ahead, I'm excited about strategies that enhance the interplay between life's biology and Earth's physical and chemical processes. This could be a more harmonious and efficient path than others like enhanced weathering. So, here's the hopeful takeaway: the implications from our work open up the possibility of reshaping Earth - a bold move called terraforming - to create a vibrant future. Let's reimagine what's possible together.

Let me walk you through the key implications from our new Nature paper on Earth's geological carbon cycle. First things first: the natural CO2 release we identified is tiny compared to human emissions. So I don't see this work as "bad news" at all.

In fact, I believe it provides a vital perspective for shaping our future climate strategies It gives us a deeper understanding of how our climate has remained stable for long enough for life to evolve and thrive, and how we might ensure its future stability.

To understand this, let's consider the concept of Earth's "thermostat," a metaphor that refers to the natural processes that have regulated our planet's climate over the course of hundreds of millions of years of Life’s evolution, helping to keep it within a habitable range.

Understanding Earth's Climate: The Idea of a 'Thermostat'

It's a self-regulating system, meaning that it responds to changes in the environment in ways that maintain its balance.

The key to this "thermostat" is a process known as chemical weathering. Here's the long-held consensus on how it works:

When the Earth gets warmer, the rate of chemical weathering increases. This is because higher temperatures speed up the chemical reactions that allow silicate minerals in rocks to react with CO2. This reaction absorbs CO2 and eventually transforms it into carbonate rocks in the oceans, effectively removing the CO2 from the atmosphere and storing it in rock form. This process cools the Earth down, counteracting the initial warming.

This is a negative feedback loop because the process responds to changes in a way that counteracts those changes. If the Earth gets warmer, the thermostat turns up the weathering, which cools the Earth down again.

A New Perspective: Life's Role in the Carbon Cycle

So for a long time, the consensus was that this thermostat worked because the CO2 emitted over time by volcanoes was counteracted by the CO2 being absorbed and locked back into rocks through a process known as silicate weathering. This process was seen as a key player in the inorganic carbon cycle.

However, our study found that weathering of organic carbon in rocks—carbon produced and locked up by plants and animals millions of years ago—can release as much CO2. This means that the same rock weathering process that draws down CO2 can also release it, depending on whether it's weathering silicate minerals or organic carbon. We found that the amount of CO2 released from weathering organic carbon in rocks is high enough to offset the CO2 drawn down by weathering the silicate in rocks.

So for all we know, since this is a slow process, for tens and hundreds of millions of years Earth has remained a stable climate despite the supposed rock weathering CO2 sink not being a sink at all, or at least certainly not big enough.

This supports a new perspective: the Earth's carbon cycle, its thermostat, is not predominantly inorganic, but predominantly organic. That means that carbon produced and locked up by biology, by living beings, has been at least as important or even more so than the processes that are solely chemical and physical in nature.

This understanding offers a hopeful message: Life itself has played a larger role in maintaining Earth's habitable climate than we previously thought. This insight influences our approach to climate action, suggesting that we should be inspired by biology and its interaction with physical and chemical processes to sequester CO2.

I also need to counter the notion that this is about saying everything will be fine. Here, it's important to remember that this thermostat has not been infallible. Life itself has sometimes caused significant disruptions, such as inducing a snowball Earth condition when photosynthesis evolved and dismantled the methane greenhouse atmosphere. This happened about 700 million years ago during the dawn of life on Earth. 

In our planet’s climate history, we see that we have a sort of thermostat and it has its own shortcomings and dynamics, which means we have seen a lot of dramatic climatic changes over Earth's long long history. But generally, it has remained at least within a habitable zone.

And so that leads to many of the unanswered questions I posed in the discussion of the Nature article. But ultimately I think what this means for action, is that we should be inspired by biology and its interaction with physical and chemical processes to lock up CO2.

Figure 3 from Zondervan et al., "Rock organic carbon oxidation CO2 release offsets silicate weathering sink," Nature, 2023. https://doi.org/10.1038/s41586-023-06581-9

Re-thinking Climate Strategies: Beyond Enhanced Weathering

One approach to solving climate that has been proposed is "enhanced weathering." This involves accelerating the slow process of chemical weathering of silicate in rock. The concept entails crushing and spreading rock like basalt or olivine, which react with and absorb CO2. However, this approach is energy-intensive and could have unforeseen impacts on biological systems such as soils. There are no silver bullets but I think we can do better.

A direction I find more interesting is inspired by the role of life in the carbon cycle: to enhance the process of burying organic carbon on the seafloor. This process starts with the biological production of biomass, which ends up in soils and is ultimately washed offshore through rivers.

What happens with that organic carbon and whether it is locked up for millions of years subsequently relies on whether that carbon oxidised and is released back into the atmosphere, being part of a short-term cycle, or being locked up on the seafloor into the long-term cycle: that is what we want.

I’ve been keeping my eye on some research since I realised what our results meant. If the organic carbon that ends up in oceans can bind to clay particles and sink to the seafloor before it can be released back into the atmosphere, it becomes part of the long-term carbon cycle. This approach is probably more harmonious with biological systems and potentially more efficient.

That's an example of where biological physical and chemical processes interact to lock up carbon. And I find that a very interesting and promising direction.

So yes when we're talking about ecological land restoration, putting more life on land, building up more biomass, and sucking that CO2 out: we're both enhancing life rather than threatening it (ie. potentially from any unintended or currently not yet understood side effects from enhanced weathering), and if we play it right we could be locking up carbon not just for the short term but for the long term, and in bigger quantities than with enhanced weathering.

That excites me. Also, since life replicates itself it might be much more efficient than spending all that energy to crush and distribute rocks for example. Just to be clear I'm not opposed to all enhanced weathering initiatives since there are some successful approaches like pumping CO2 directly into basalt reservoirs underground, where you don't crush and spread the basalt onto land but instead put the CO2 into the rock underground.

But the main point I want to make is that I think our work supports ideas that are very hopeful, and it is a reason why I'm next focusing on enhancing those feedbacks between the biology of life, the physical and chemical processes in landscapes, and on the Earth surface more broadly. 

Unleashing Life's Symphony: A Vision for Earth's Future

The deeper understanding of the carbon cycle including biology supports ideas reminiscent of the Gaia hypothesis. This concept, proposed by James Lovelock, suggests that life as part of the planetary system can regulate its own environment to benefit its thriving. While this idea sometimes goes too far and can seem a bit naive given life's capacity to cause significant climate disturbances, it's a concept worth referencing. Our findings underscore the critical role of life, in concert with physical and chemical processes, in maintaining Earth's climate.

So, when I talk about "unleashing life's symphony," I'm referencing this Gaian perspective. Our study suggests that life has been a central player in the geological-biological carbon cycle, inspiring us to look for strategies that enhance these natural processes. The symphony metaphor encapsulates the dynamic and complex interactions between all components of our planet—biology, geology, chemistry, and physics—just like the diverse instruments in an orchestra creating a harmonious whole.

Rather than trying to simply recreate conditions from an idealized past era, I think we should reimagine what's possible. Crafting ecosystems resilient to ongoing changes, using our knowledge. We must acknowledge we've profoundly altered Earth's systems. There's no turning back the clock, and often, we don't even have a clear understanding of what the "clock" initially looked like.

Recent archaeological research, including studies I've been involved with, shows that human impacts on the Earth's environment extend far deeper into history than we previously thought. These impacts have shaped the Earth system in profound ways, many of which are still not completely understood. For instance, our work in the Tropical Andes has shown that before European arrival humans likely occupied a significant portion of the region, influencing its ecology in ways we're still discovering.

Such findings suggest that many environments we might think of as "untouched" have, in fact, been shaped by human activities for millennia. These past human impacts have left a lasting legacy on the land, influencing everything from forest dynamics to species distributions. As we move forward, we must bear in mind this complex history of human-environment interactions.

This realization brings a new dimension to the concept of "terraforming." In the context of Earth, terraforming refers to the intentional stewarding of the planet's geological and biological systems to make them more beneficial for life. It's an audacious vision that goes beyond simply restoring Earth to a presumed pre-human state and instead involves reimagining the potential of our planet.

Like an orchestra, Earth's instruments have gone out of tune. But fixation on the past limits imagination of the future. Instead of recreating dated harmonies, let's compose new melodies. What majestic symphonies might arise through terraforming, guided by human intelligence and wisdom?

That's the spirit needed to unleash life's symphony. Not trying to recreate some elusive past state, but pushing boundaries. Using knowledge and technology to find novel combinations between organisms and environments.

There are endless possibilities we haven't yet imagined. Bioremediation, synthetic biology, regenerative agriculture - these are just first attempts. The masterpiece is still being written.

We must proceed with wisdom and care. But the future unwritten score awaits our creativity. What majestic crescendos might we compose through terraforming Earth?

More on that later...