It's like - energy, but put in a form that will easily transfer to other things and be used by them, almost, but not quite completely geared towards living things, and certainly favoring them. Some of the essence dissipates into the bacteria in the air, but not all of what's dissipating is going to living things. Some of it helps give the wind around them a bit of speed, the change so slight and nearly imperceptible that if he were not studying the essence and its effects so intently it would be hard to notice. Some of it goes into the air and is carried off to be utilized by something else; the ground, mostly. Where it goes into the ground it's gobbled up to feed a land that is very starved.

It feels - unprototyped, easily malleable. Somewhat like a stem cell - easily able to be adapted into other things and then staying that way. With a bit of a push you could probably even get it into a non-living form, but that feels highly advanced and difficult to accomplish. It looks like it might be possible to tell what's been adapted from it, though he'd have to have an example of it to tell for sure.