I can’t remember where I read the theory, but apparently the salinity of our bodies matches that of primordial seas, so in a sense we never really left the oceans. Our micro-organic aquatic ancestors simply constructed meatbag spaceships with artificial life-support aquatic environments inside to explore beyond their oceanic home world. Much as we might construct generation starships in the future to travel to Alpha Centauri. Air-breathing multi-cellular life forms constitute the space program of primordial single-celled life. They get the missing resources of their primordial environment through clever artificial means, just as we might eventually mine our essential minerals from asteroids or gas clouds we fly by in outer space.
One of the effects of this evolutionary history is that all air-breathing life has to seek out perhaps the most important chemical that’s ubiquitous in the oceans but not trivial to find on land: salt. Salt-seeking is one of the most fundamental behaviors of terrestrial life. Animals in the wild seek out salt licks even at great risk of predation. Humans with salt deficiencies have serious problems, and beyond a point of salt deprivation, you die.

(NJR ZA, Wikimedia Commons, CC-BY-SA 3.0)
This evolutionary history struck me as an interesting metaphor, and a superior alternative to the more familiar metaphor of “coming up for air.”
Oxygen, whether extracted from the air or water, is critical on very short time-scales, even by the standards of the lifespans of micro-organisms. You die in minutes without it. So the idea that you might be so swamped by work that you need to “come up for air” is evocative but not quite coherent. I can think of coming up for other kinds of macro-nutrients like water and food at the time scales of uninterrupted work (hours/days) but not air. If you’ve ever actually had to “come up for air” (I did a couple of times as a kid while learning to swim) you know it’s not some sort of restorative break. It’s a panic-inducing emergency of a sort that is not metaphorically like anything else.
But salt-seeking… now that’s an interesting metaphor that operates on a whole different time-scale. If you don’t lose any salt to perspiration, you can go without salt intake for days to weeks (it’s not so much a consumable nutrient as a sort of electrolyte concentration thing I guess).
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