Olivia Judson published a very interesting paper this March on “Nature Ecology & Evolution“. It is a wonderful cavalcade along 4 billion years of the history of the Earth, seeing it in terms of five “metabolic revolutions.” It is an approach that goes in parallel with a paper that I wrote last year on BERQ; even though I focussed on the future rather than on the past. But my paper was very much along the same lines, noting how some of some of the major discontinuities in the Earth’s geological record are caused by metabolic changes. That is, the Earth’s changes as the life inhabiting it “learns” how to exploit the potential gradients offered by the environment: geochemical energy at the very beginning and, later on, solar energy.
Seen in these terms, the Earth system is a gigantic autocatalytic reaction that was ignited some four billion years ago, when the planet became cool enough to have liquid water on its surface. Since then, it has been flaring in a slow-motion explosion that has been going faster and faster for billions of years, until it is literally engulfing the whole planet, sending offshoots to other planets of the solar system and even outside it.
Judson correctly identifies the ability to control fire as the latest feature of this ongoing explosion. Fire is a characteristic ability of human beings and can be argued that it is the defining feature of the latest time subdivision of the planet’s history: the Anthropocene.
Judson stops with fire, calling it “a source of energy” and proposing that “The technology of fire may also, perhaps, mark an inflection point for the Solar System and beyond. Spacecraft from Earth may, intentionally or not, take Earthly life to other celestial objects.” Here, I think the paper goes somewhat astray. Calling fire a “source” of energy is not wrong, but we need to distinguish whether we intend fire as the combustion of wood, that humans have been using for more than a million years, and the combustion of fossil hydrocarbons, used only during the past few centuries. There is a big difference: wood fires could never take humans to contemplate the idea of expanding beyond their planetary boundaries. But fossil energy could fuel this expansion at most for a few centuries and this big fire is already on its way to exhaustion. If the Anthropocene is to be based on fossil fuels, it is destined to fade away rather rapidly.
The great chemical reaction is still flaring up and its expansion is going to take us somewhere far away, even though, at present, we can’t say where.
A new lifeform, just appeared in the Earth’s ecosystem:
(**) The supporters of nuclear energy may argue that the next metabolic revolution should be seen as the production of energy from nuclear fission or fusion. The problem is that the resources of fissionable material in the whole solar system are too small that they could hardly fuel a truly new geological epoch. As for fusion, we haven’t found a technology able to control it in such a way to make it an earth-based source of energy and it may very well be that such a technology doesn’t exist. But, on the sun, fusion works very well, so why bother?