How the First Trees Nearly Froze the Earth 

December 21, 2022

And what the answer can teach us about reversing climate change. 

We can trace the modern age through a blink in geological time, from the first steam engines to a telescope floating a million miles from Earth. It all started with the discovery and combustion of coal, which powered the steam engines that drove the Industrial Revolution and provided an efficient fuel for reliably turning iron ore into steel. But our story begins far earlier, over 300 million years ago, when those first coal deposits formed. In studying their creation, we can learn more about how our climate functions, the massive power of plants at scale, and how we as humans can reverse the effects of climate change. 

The Carboniferous Period

(359 to 299 million years ago) 

In the Carboniferous period, CO2 concentration plummeted tenfold from over 2000 ppm to about 200 ppm. As temperatures dropped, ice sheets spread forth from the poles, launching a massive ice age. 

What caused this dramatic shift? In short, plants. 

However, it wasn’t just the presence of the world's first vast forests that sparked the change. It was the environment in which they thrived. At this time, the planet had yet to host large terrestrial herbivores or fungi that were particularly adept at digesting wood. As a result, dead trees simply lay where they fell, without decomposing efficiently, and they were eventually buried by subsequent vegetation. Millions of years of this process sequestered enough carbon to raise the oxygen concentration of the atmosphere to 35% (today it is 20%).

To be more specific, in order to grow tall enough to compete with other plants for light, the early trees began to produce a strengthening material, lignin, to give their wood compressive strength. While lignin is now digestible by a group known as the white rot fungi (named for the white and papery cellulose they leave behind after dissolving the lignin), back in the Carboniferous lignin was almost as indigestible as plastics are now. It took 30 million years for fungi to develop an enzyme, lignin peroxidase, that could successfully break down lignin and use it as a carbon source for aerobic respiration.

This age of oxygen saw the evolution of giant insects, whose respiratory system depended on elevated oxygen levels, and terrifyingly destructive firestorms, where even wet wood would burn. 

In the Carboniferous period, atmospheric oxygen levels peaked around 35%, producing some of the largest arthropods the world has seen — from millipedes the size of basketball players to dragonflies the size of seagulls. Photo cred: Deviantart

The ice age finally ended when fungi, termites, and herbivorous vertebrates evolved and unleashed carbon back into the atmosphere that was previously trapped in dead vegetation. Much of the coal we burn now represents carbon removed from the atmosphere during this ice age.

Usually when a dead plant or animal decays, microbes decompose it and release CO2 in the process. But as great masses of dead plants became buried under swamps and out of contact with oxygen, the level of carbon dioxide in the atmosphere steadily dropped and the climate cooled. Photo cred: National Geographic

Takeaways for the Anthropocene 


Today, we face a carbon dioxide surplus driven by our appetite for burning ancient stores of fossil fuels buried underground. We don’t have the luxury of waiting for the right conditions for a climatic rebalancing to occur again, such as an event like the sinking of vast forests into swampland. In order to reverse the effects of climate change, we have to react within the scale of a human lifetime. This is where biotechnology comes in. As humans, we have developed technology that allows us to work with the inherent power of plants, learn from their past carbon capture successes, and speed up a rebalancing process that would otherwise unfold over geological timescales. Learning from the Carboniferous Period, Living Carbon is working to (1) increase the rate of photosynthesis so plants can store more carbon, faster, on less land, and (2) increase the durability of stored carbon. We are also exploring more permanent carbon storage which would mirror the effect of plants sinking to the bottom of ancient swamps by preventing biomass from decomposing for thousands or millions of years.

The good news: we don’t need to recreate the scale of the Carboniferous Period, where CO2 levels fell tenfold. In contrast, we’ve got to get from 420ppm today, back down to the “goldilocks”’ 350ppm. Now is the narrow launch window for climate solutions. We know we can store carbon dioxide with the same level of ingenuity that allowed us to release it. 

This post was part of our Deep Time Series. Continue reading the next post: This Fern is the Best Analog We Have for Stopping Climate Change

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