Sciency Words: (proper noun) a special series here on Planet Pailly focusing on the definitions and etymologies of science or science-related terms. Today’s Sciency Word is:
Based on what Google ngrams has to tell me, it looks like “euphotic” and “euphotic zone” entered the English lexicon right at the start of the 20th Century, then really caught on circa 1940.
The word euphotic is a combination of Greek words and means something like “good lighting” or “well lit.” In the field of marine biology, the euphotic zone refers to the topmost layer of the ocean, or any body of water, where there’s still enough sunlight for photosynthesis to occur.
My first encounter with this term was in this paper by astrophysicists Carl Sagan and Edwin Salpeter. Sagan and Salpeter sort of co-opted this term from marine biologists and applied it to the layer of Jupiter’s atmosphere where—hypothetically speaking—Jupiterian life might exist.
I don’t see any reason why the term could not also by used for other planets as well. There’s a euphotic zone just above the cloud tops of Venus. The same could be said about Saturn or Uranus. Or maybe if the ice is thin enough, we may find euphotic zones right beneath the surfaces of Europa or Enceladus.
Of course just because a planet has a euphotic zone, that doesn’t mean photosynthetic organisms are living there. And also there are plenty of ecosystems here on Earth that do not depend on photosynthesis and that don’t exist anywhere near a euphotic zone.
Still, I’m very glad to have picked up this term. The concept of euphotic zones can be very helpful in any discussion of where alien life may or may not be hiding.