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.

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