By "essence," what do you mean, exactly?We can assume for curiosity and logical discussion. Its always good to want to know the essence of life. I would say that its God.
How is God an essence? How do you know there is a God? (careful -- don't go in circles, here).
"Life" is biologically problematic. Does it have a unique, 'essential' feature? What would that be?
Established, cellular life is pretty easily recognized, but what about its progenitors; components of life, self-replicating, lifelike structures, proto-life?
It seems to me that life developed gradually; that there's an arbitrary spectrum of aliveness.
Unless, of course, you believe in magic poofing.