My theory or abstract beliefs you don't want -- but dude, I am not the Supreme Creator, and I don't have perfect knowledge into the nature of things.
So how can I give you anything EXCEPT for "theory or abstract beliefs," since I can't directly access the secrets of life with either my eyes or my brain?
As for your main question: I can't give you scriptural backup for this, but I think "life" began in a chemical soup in the primordial seas of Earth, perhaps 2 billion years ago or more.
And I think it's perpetuated itself and become more varied and gloriously complicated ever since. Life today is organized into natural food chains, arranged in complicated ecosystems, perpetuated by the sex lives of most animals and plants and by the asexual reproduction of certain plants -- eg ferns -- and by the mitosis of unicellular plants and animals.
Are viruses alive? I think it's disputed, but to the extent that viruses are alive, life also is perpetuated by the spreading of viruses, by the ability of their DNA and RNA to penetrate the cells of other living things and turn those cells into little chemical-biological factories for the production of more viruses.
That's my personal sense of where life begins and how it continues, based on my science classes.
If you're looking for Christian scriptural authority, however, I suppose you could say that "life" began when God allegedly created the heavens & the earth & all the living things that cover the earth an estimated 6,600 years ago, as per the Book of Genesis.
If you think the spirit of God is also the "breath of life," however, if you think that things come alive only when God breathes his spirit into then, then maybe you should conclude that life in the ultimate sense is as old as God is, although it's only for about the last 7,000 years that God's spirit has been lent to living creatures on Earth to give us animation.