In a blog post from a few years back, speculating about the Fermi Paradox, I discussed why the percentage of intelligent life-forms that develop high-tech civilization you can see across interstellar distances might be very low. (There’s a whole series of posts on this topic, starting here).

Image ID 6654988, ⓒ Yarygin,

That old blog post series came back to me a few days ago. I stumbled onto a clickbait site that claimed that trees lived tens of millions of years before any organism evolved that could break down the biopolymers that make up stems and trunks.. In other words, dead trees couldn’t rot. Let’s call them zombie trees. (Here’s a page on that topic from a British timber merchant that doesn’t have the same Google ad repeated 50 times between the AI-generated content).

What happened then? Non-rotting zombie trees piled up in the bottoms of swamps, under layers of sediments, and eventually became the coal and oil reserves we are exploiting today.

From Zombie Trees to the Fermi Paradox

Wait, how does that relate to the Fermi Paradox? One day at lunch in the cafeteria at Los Alamos National Lab, Nobel Prize winner Enrico Fermi raised the following point. The solar system is fairly young compared to the Milky Way galaxy and the universe as a whole. Though are sample size is pretty small, it seems likely that solar systems have planets. Planets on which life can arise. Evolve intelligence. Build a high-tech civilization that can produce detectable radio waves or eventually travel between the stars.

From these factors, the galaxy should be teeming with intelligent aliens.

Where are they?

The Drake Equation provides a framework for thinking about why we haven’t detected intelligent high-tech aliens. It’s basically a bunch of probabilities of various events, multiplied together. The term we’ll talk about today is fc = the fraction of civilizations that develop a technology that releases detectable signs of their existence into space.

Humanity’s tech tree reached that point a few decades ago. (Broadcast episodes of Star Trek have reached the sun-like, known-exoplanet star Iota Horologii about 55 LY away). But what did it take to develop that tech? Energy. A lot of it. More than the Romans could get from burning trees or working draft animals. More than medieval Europeans could get from waterwheels or windmills. Energy that could only be extracted in the necessary amounts by burning fossil carbon, i.e., coal and oil.

Where did coal come from again?

Zombie trees come back here. Our coal and oil might only have formed from an evolutionary accident. Other possiblities could have happened. Suppose microorganisms needed only tens of thousands, instead of tens of millions, of years to evolve the enzyme pathways to digest cellulose and lignin. Or suppose trees evolved to use other long-chain carbohydrates for their structure, and those other long-chain carbohydrates were ones microorganisms could already digest.

Either way, those dead trees millions of years ago would have been rapidly broken down into microorganism food, and from there, to CO2, instead of being preserved and compressed by geological processes into coal and oil. Without providing fuel for a future intelligent tool-using civilization to go from medieval European technology to all the advances in the modern part of the tech tree.

tl;dr we only have coal and oil to burn thanks to an evolutionary accident. Without that accident, an intelligent tool-using civ would have to jump from medieval European energy sources directly to nuclear fission. This jump seems really unlikely. As a result, if most planets didn’t have that evolutionary accident, most intelligent life-forms would never develop a high-tech civilization.

(Hey, I just discovered the backstory of the planet Valoduria in my Analog short story Return Blessing.)

What if the zombie trees argument is wrong?

This conclusion holds even if the lack of lignin degradation camp has it wrong about coal deposits. This paper poo-poos that explanation, arguing instead that “Evidence for lignin degradation—including fungal—was ubiquitous, and absence of lignin decay would have profoundly disrupted the carbon cycle. Instead, coal accumulation patterns implicate a unique combination of climate and tectonics during Pangea formation.” (emphasis mine)

To sum up, whether the accident was biochemical or climatological+geological, coal and oil deposits are an accident. Without them, the odds of human beings advancing past medieval European energy consumption on the tech tree would be very low.

You know what else this makes very low? The value of fc in the Drake Equation.

Yet another argument that the Great Filter is behind us.