How do we know that some form of life is actually alive (not dead)? Answer: the chemicals which keep everything going are still doing what they do.
We may be the most complex form of life on the planet, but we are kept going by our chemicals, just like all the others.
Our chemicals include nitrogen, oxygen, etc., etc. But the ones which really matter to us from moment to moment are the tiny ones, which only show up under the microscope: hormones and neurotransmitters, that regulate processes throughout the body. The ones that we especially welcome? adrenalin, dopamine, endorphins, serotonin …