The thickest basis of life is simply conciousness. Self awareness and awareness in general.
Life began when conciouness began. Conciousness is the result of a series of complex functions. Conciousness must be maintained through a series of means (consumption for example)
Early life was obviously simpler than the Life which came later. Hence evolution.
Think of it this way: Was there any life involved when the stars formed, when the worlds cooled, and when the worlds took shape ? There were processes already occuring before life was there to witness it.
If the sun is not alive, then how did it form ? If the Earth is not alive, then how did it cool, how does it always change ? What's forcing it to rotate, and revolve around the sun ?
It's clear that there are processes in nature that occur, that do not involve conciousness. Trees are alive, but are they self aware ? If they are not self aware, then who are we to say they aren't alive ? Trees grow and consume and die, so they clearly are alive.
The point is, before "Life began" there have been active processes in this universe already occuring.
Simple processes lead to more complex processes. Simple Life lead to more complicated life.
Organic bodies are composed of inorganic molecules, the same inorganic molecules which rocks, water, and soil are composed of.
Simple processes of atoms and molecules lead to cellular structures, which began to form thier own processes as well. Active processes have already existed before cellular life began.
Cellular Life, simply as it is, lead to multi-cellular life, which in turn lead to more complex life forms.
If you take apart a life form, you will find that each peice of what the life form is composed of, is not alive. Life is the result of the union of these factors, processes, and conditions.
LIFE CAN COME AND HAS COME FROM NON LIFE
Life is sustained through conditions (consumption, respitory exchange, procreation)