The Search for Extraterrestrial Intelligence (SETI) focuses on detecting technological alien civilisations, typically through their radio transmissions.
Various steps are thought to be crucial for the emergence of any advanced civilisation, but Lincoln Taiz from the University of California and his colleagues say one question receives little scientific attention: how likely is it for intelligent aliens to go on to develop detectable technology?
It’s commonly assumed that once intelligence emerges on an Earth-like planet, developing complex technology is inevitable.
But might quirks of Earth’s history have set the stage for humanity to progress from early civilisations, supported by agriculture and simple metallurgy, onwards to advanced technology?
More on alien life
Central to their argument is the role of fossil fuels in driving the Industrial Revolution that ultimately gave rise to our current advanced technological civilisation.
The geological formation of fossil fuels – specifically large deposits of easily accessible coal – came down to a series of contingencies that might not occur on other Earth-like planets.
Indeed, one of Taiz’s co-authors is palaeontologist Peter Ward at the University of Washington, co-author of the 2000 book Rare Earth, which put forward the hypothesis that our own planet is very special in its astrophysical and geological conditions that enabled the emergence of complex life.
This paper effectively applies that same ‘rare Earth’ mindset to technological development.
The case for coal
Coal played a crucial role through the 19th century in driving the Industrial Revolution, in smelting iron ore, forging steel tools and machine parts, and powering steam engines.
In 1720, iron production in Britain alone would have needed 830,000 tonnes of wood turned into charcoal to fuel the furnaces – that would have required a forest almost the size of Great Britain to be felled every year.
It was ancient forests, dug up as coal, that supplied this critical energy gap.
They point out that deposits of other fossil fuels – oil and gas – lie much deeper underground, so the earlier coal-fired stage of industrialisation was necessary to enable them to be exploited.
Similarly, alternatives such as hydropower or solar power could only be developed to deliver sufficient energy by the complex metallurgy and infrastructure that came out of the Industrial Revolution.
They believe it unlikely that any civilisation could leapfrog over fossil fuels entirely and go straight to such renewable energy sources.
So, whether extraterrestrial civilisations could ever develop advanced technology hinges on how common large deposits of coal are on other planets.
Most of the coal used in the Industrial Revolution was created during the Carboniferous period, when the supercontinent Pangea was forming.
Tropical swamp forests not only grew vigorously, but also became buried, preserving their biomass to be converted to coal underground.
This particular combination of plate tectonic and climatic conditions, they say, is so unusual that it’s unlikely to have been common on other Earth-like planets.
I’m not entirely convinced by all their points, but they raise a very interesting new argument within SETI: maybe technological civilisations are rare because coal is rare.
Lewis Dartnell was reading How Common are Oxygenic Photosynthesis and Large Coal Deposits on Exoplanets? by Lincoln Taiz et al. Read it online at Cambridge Core
