Nearly 50 years ago, on Christmas Eve 1968, NASA astronaut Bill Anders saw Earth rising over the lunar horizon as the Apollo 8 spacecraft circled the Moon. “Oh my God!” Anders said, according to an audio recording of the flight. “Look at that picture over there! There's the Earth coming up. Wow, that's pretty.”
“Hey, don't take that [photo],” joked astronaut Frank Borman. “It's not scheduled.”
Of course, Anders did take the famous “Earthrise” photo, which is now considered an immensely influential snapshot and a key inspiration for environmental movements that gained traction in the 1970s.
“Earthrise” also provided the visual groundwork for one of the most controversial ideas in modern scientific history—the Gaia hypothesis. The brainchild of chemist James Lovelock, the hypothesis imagines Earth as one superorganism called Gaia; a living thing built from intricate coevolutionary interactions between the ecological and geological spheres. The planet’s properties—from salinity, to oxygenation, to biodiversity—are generated to provide optimal conditions for the continued propagation of life, according to the hypothesis.
Lovelock widely popularized the idea with microbiologist Lynn Margulis in the 1970s, though similar proposals were developed by Russian scientists around the turn of the 20th century. It’s easy to see why “Earthrise,” a shot that captured our entire planet in its aperture, revived these holistic frameworks in Earth science.
The Gaia hypothesis has also sparked decades of backlash, most of which boil down to characterizations of the idea as pseudoscientific. Evolutionary biologist Richard Dawkins rejected the hypothesis on many grounds, including that Earth can’t be considered a living being because it does not adhere to basic Darwinian principles like adaptation and reproduction.
This particular criticism might be resolved now that we have entered the age of exoplanet discovery, according to Roberto Cazzolla Gatti, a research associate and evolutionary biologist at Purdue University.
In a recent study published in Futures, Gatti proposes that human beings could act as the germinal cells for our planet, and potentially other worlds, because we have mastered spaceflight. He envisions finding “mates” for Earth by launching spacecraft containing “biophores,” which would be cultures of our hardiest organisms, such as extremophile bacteria.
These biophore-carrying space capsules could be dispersed to nearby star systems where they might germinate life on new worlds like spacefaring versions of plant seeds. This idea of seeding Earth life on other worlds isn’t new, of course, but Gatti explores the potential outcomes and strategies in light of recent exoplanet discoveries.
“If there is something that we can do to continue life in the universe, why shouldn’t we?” Gatti asked, in a phone call with Motherboard. “We have this big power, not because we are the best or because we are the most important. It happened by chance and because of evolution.”
“I would expect that on other planets, there are other species that are advanced enough to produce something that could act like a sperm cell to take the genes from the planet’s body and spread them,” he added.
In essence, humans could be Mother Earth’s matchmaker if we set our minds to it. This would further substantiate the Gaia hypothesis’ conceit of our planet as a living superorganism capable of reproduction.
It may seem like a far out idea, but scientists have riffed on the “panspermia” hypothesis, which suggests life on Earth could have been seeded by an extraterrestrial body, for decades. If there’s a chance that the universe naturally spreads the ingredients for life, is it that weird for humans to channel panspermia in a directed and purposeful way?
“If you consider our planet a reproductive unit, we have many different options in the universe,” Gatti said. “It will take a while. We won’t be able to do it tomorrow. We need different minds with different backgrounds and ideas to work together with a specific purpose—to reproduce our planet.”
Read More: Did Life on Earth Come From Outer Space?
This doesn’t mean we would be terraforming, or aiming to make exoplanets into Earth twins. The goal is to spread basic forms of life and let them take their own evolutionary courses on alien worlds, whatever that might be. Judging by the way life developed on Earth, any biophores that survive dispersal to other planets would likely take millions or even billions of years to evolve into more complex forms of life. Indeed, the journey to other star systems alone could take thousands or millions of years.
All of this takes for granted that humans should aim to spread life elsewhere in the universe. There is an ethical argument to be made against such an endeavor because we risk becoming a cosmic invasive species. If an exoplanet already hosts life, biophores from Earth could disrupt or even destroy it.
But maybe Earth life would adapt to an alien ecosystem, Gatti told me, perhaps even sharing genes with it in a case of interstellar sexual reproduction. There’s also the more ethically comfortable idea of asexual reproduction, which would involve planting biophores on habitable—but uninhabited—worlds, where they could start a new riff on Earth life. “Most of the clades on our own planet use asexual reproduction,” Gatti noted. “It works well.”
Proponents of the Gaia hypothesis often use the metaphor of the planet as a body, with humans and other lifeforms acting as cells that unknowingly contribute to the health of the whole entity. In Gatti’s view, humans have a choice to be life-enhancing mechanisms in this body, like germinal cells, or life-destroying mechanisms, like cancer cells, which negatively affect our host’s biodiversity.
This perspective reflects broader paradigm shifts about the human role on our world that partly originated with the popularization of “Earthrise” a half-century ago. Upon viewing Earth from space, astronauts frequently report feelings of euphoria or revelation at taking in our world’s interconnectedness and fragility. This experience is known as “the overview effect,” a term coined by author Frank White in the 1980s.
On this momentous anniversary of “Earthrise,” perhaps it’s time to reflect not only on what the image means for the human future on Earth, but also the future of Earth’s life in the universe.
Our world will be swallowed by the Sun in a few billion years as it expands into a red giant. But the incredible genetic experiments that Earth nourished could potentially outlive the planet. Over the past 20 years, scientists have discovered thousands of exoplanets in alien star systems. Some may host alien life already—and perhaps some could be seeded with life from Earth.
“We do not need to wait to find life in the universe,” Gatti said. “We could be the germinal elements to spread life out.”
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