Earthlight
“This is earthlight, not sunlight. As the superheated water cools against its surroundings, it emits photons – thermal radiation. The light from vents is strong enough that, in the modern day, a species of bacterium is known to use it for photosynthesis, some 2.5 kilometres below the reaches of the sun. Perhaps one of the Silurian bacteria is doing the same”
Excerpt From: Halliday, Thomas. “Otherlands.” Random House Publishing Group, 2022-02-01. Apple Books.