Viv,....I am not saying it's oxygen alone. The force is the air we breathe composite,but of course mostly oxygen.
You are of course correct to say we owe much more to our existence, and as you say without photosynthesis no oxygen. But you digress. The context is HUMAN spirit. Photosynthesis provided us with the force we humans cannot exist without.
The unborn child relies on the oxygen from its mother as did she and so on back. When the umbilical chord is cut how does the now independent child survive,? To what force does it owe its continuation of life? The force of air in its lungs. That is the spirit of life which then in turn is fundamental to our continuing our development until finally our last breath goes out and as some would say his/her spirit is finally gone, in other words no more. breath no more spirit for that individual.
I posed a question to you in a previous post have you any opinion?
Best wishes