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The burning of fossil fuels — coal, oil and gas — propelled humanity into the industrial revolution, remaking civilization in its wake. Gasoline powers many of the cars we drive; coal and natural gas are central to global energy. But if aliens were building their own society, would they have to go down the same path as humanity, relying on fossil fuels to build their advanced civilization? Or could they find an alternative?
To build a modern civilization, aliens would likely need to use a source of energy that's just as abundant as fossil fuels, said Lewis Dartnell, an astrobiologist and author of "The Knowledge: How to Rebuild Our World from Scratch" (Penguin Press, 2014). It would be hard for them to simply bypass the production of fossil fuels, he noted.
Dartnell drew a parallel with humans: In the 18th century, the world entered the industrial revolution by tapping into what appeared to be a limitless source of energy. Coal burned longer and produced more power than wood and charcoal.
"Prior to that, energy was the fundamental limitation on how much you could do," he said. "It would limit how much you could mine and move things around, what you could build, and what you could make."
The question of whether humans could have bypassed fossil fuels to reach alternative energy sources is "somewhat of a chicken-and-egg dilemma," Dartnell told Live Science. For instance, producing solar panels requires silicon, and extracting and refining this element demands a significant amount of energy.
The easiest way for intelligent aliens to create fuel would be to start by burning stuff, like humans did, until they can move to other sources of energy. They could perhaps harness the light of a star or of the kinetic energy of the wind. But wind energy on its own would not create the high temperatures needed for the smelting, forging and casting of metals, which would be needed for industrialization, Dartnell said.
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Meanwhile, hydropower would only work if the planet had significant amounts of accessible liquid, which most planets we've found don't possess, added Seth Shostak, an astronomer and director of the Search for Extraterrestrial Intelligence (SETI) Institute.
Could other planets have fossil fuels?
Scientists still haven't found a planet with abundant oxygen in its atmosphere, though trace amounts have been found on Mars, Venus and Jupiter's moon Europa. Oxygen is the key ingredient in burning fossil fuels because it enables combustion, which is what releases the energy stored in coal, oil and gas.
Fossil fuels are created from life — they're the transformed remains of plants and animals that lived hundreds of millions of years ago. Dartnell suggested that plate tectonics are a crucial part of the puzzle of how these life forms came to exist. "There's good reason to suspect that in order to have intelligent life on an Earth-like planet, you need to have plate tectonics to regulate the climate for long periods of time," he said.
A 2022study by researchers at the University of Sydney reported how Earth's tectonic plates move carbon between the deep Earth and the surface, forming what they call a "carbon conveyor belt." This process is key to maintaining Earth's "Goldilocks" climate, making the planet habitable, according to the study. What's more, plate tectonics also results in continental drift and the creation of conditions that produce large amounts of coal, a fossil fuel, he added.
Coal, the buried and transformed remains of ancient plants that lived in swampy forests, takes hundreds of millions of years to form.
(Image credit: Zaporizhzhia vector via Shutterstock)
Put another way, plate tectonics can help pave the way for life and create conditions to help it become fossil fuels; it can also create ideal conditions for life that may become intelligent enough to harness those fuels.
"In a sense, you get a two-for-one," Dartnell said. "If you have a planet with active plate tectonics, that regulates the climate, which allows for the evolution of intelligent complex life."
Scientists have yet to find another planet with active plate tectonics. Nor have they found fossil fuels in space. What they have discovered, however, is evidence of fossil fuels' chemical building blocks: hydrogen and carbon. Approximately 75% of the universe's mass is composed of hydrogen, said Shostak. Additionally, scientists have found a field of liquid hydrocarbons on Saturn's moon Titan. Intelligent aliens could, hypothetically, attempt to burn these elements to produce energy.
Of course, aliens aren't necessarily bound by the same constraints as humans, and our imagination often limits us to thinking in terms of a human timeline. "It's hard for us to predict what the aliens might do," Shostak told Live Science. It's like asking Julius Caesar what he thought the Romans would be doing with oil in 2025, when they were onlyusing small amounts of oil for lamps. "Julius would probably have some ideas, all based on Roman knowledge," he said. "He would completely miss the [mark]. You have to keep that in mind."
An intelligent alien civilization could be nothing like what we expect, Shostak added. While aliens would likely need an abundant energy source to advance their civilization, who's to say what form that energy would take? The answer could lie beyond human understanding.
Sara Hashemi is a journalist and fact-checker covering environmental justice, climate and the intersection between science and society. Her work has appeared in Sierra, Smithsonian Magazine, Maisonneuve and more. She has a master's degree in science journalism from NYU.
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