All month long, we’ve been talking about Europa, the sixth moon of Jupiter. Scientists are 99% sure that there’s an ocean of liquid water beneath Europa’s icy crust, and speculation runs rampant about possible alien life swimming around in that subsurface ocean.
I’m currently reading a book called The Zoologist’s Guide to the Galaxy, by Arik Kershenbaum. The book takes the fairly uncontroversial stance that the same evolutionary processes that shaped life on Earth would shape life on other worlds (uncontroversial among the scientific community, at least). Specific details about biochemistry or genetics might be wildly different, but general principles like natural selection are likely universal.
Other science writers follow the same premise when imagining what we might find beneath the surface of Europa. The environment is presumed to be very similar to the deepest, darkest reaches of Earth’s oceans. Therefore, the same evolutionary pressures should apply, and Europa-life should have much in common with the deep ocean creatures we find here on Earth.
For example, Europa-life would probably cluster around hydrothermal vents, or similar geological hot spots, at the bottom of the ocean. It’s nice and warm there, and there are plenty of tasty nutrients billowing up from the rocky mantle.
Another example: abyssal gigantism, which is the tendency for organisms in the deep ocean to grow to enormous sizes (compared to their shallow water cousins). Scientists aren’t 100% sure why abyssal gigantism happens, but it may have something to do with metabolic efficiency. If life in Earth’s deep oceans needs to be gigantic for the sake of metabolic efficiency, then Europa-life would probably be gigantic too.
A lot of science writers also predict that bioluminescence will be common on Europa. It’s fairly common here on Earth, especially in the deepest, darkest regions of Earth’s oceans. And as you can see in this totally legit photo from the Mariana Trench, bioluminescence is really pretty.
But while predictions about abyssal giants and hydrothermal vents make a certain logical sense to me, I’m not convinced bioluminescence makes sense on Europa. As I understand it, life on Earth developed eyes first, and bioluminescence came later.
Having some sort of light-detecting organ makes sense on a world where there’s plentiful sunlight. There’s an obvious evolutionary advantage to having eyes here on Earth. And then, if some Earth-creatures decided to swim down to the bottom of the ocean, it makes sense for them to develop bioluminescence in order to help them see each other and the environment around them (or to help them lure in food).
But the ocean on Europa lies beneath a thick shell of ice. There’s no sunlight there. There has never been sunlight there. So what is the evolutionary advantage of having eyes? And if there’s no evolutionary advantage to having eyes, what would be the evolutionary advantage of bioluminescence?
Whenever Europa-life is depicted in science fiction, it’s almost always lit up in bold, bioluminescent colors. A lot of science communicators seem to envision Europa-life that way too. And why wouldn’t they? To see all those strange alien creatures waving their glow-tentacles around—that would be an awe-inspiring sight! But as awesome as it would be to see Europa-life in all its bioluminescent glory, I cannot think of a good reason why Europa-life would evolve that ability. Can you?
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I haven’t finished reading The Zoologist’s Guide to the Galaxy yet, but what I’ve read so far is good, thought-provoking stuff. If you’re interested in what alien life might really be like, scientifically speaking, then I’d say this book is worth a look.