1. I'd say it happened as far back as around 1200 BC, during the time of the Epicurean physicists.
Simply put: The soul, our conscious selves, is atomically constituted as the brain and nervous system, thus corporeal. Like every atomic compound it slowly fades into dissolution and disperses. Given that our conscious selves cannot survive death, once the body dies, there isn't anything to keep the soul together.
2. The physical world is proof in itself. If something exists, it is comprised of physical elements and laws, and vice-versa. I'd write more but I just took a bunch of clonazepam and flurazepam..
1. You don't question the assumption that the soul is necessarily the same as the conscious which is necessarily the same as essentially a series of biologically generated electrical impulses.
Convenient to the belief that there effectively is no "abstract" concept of the soul beyond the brain and nervous system, but still nothing more than a school of thought and by no means "scientific proof".
For the record, what you have written is essentially lifted almost verbatim from common modern reductions of schools of thought - in this case the *philosophy* you describe is correctly attributable in the phrases you have used to Lucretius. And check your dates, although maybe you meant to type in 200 BC.
1200 BC in Greek civilization would have been about at the end of the reign of the at best semi-legendary Theseus.
As long as we are in 1200 BC, Plutarch gives an interesting comparison of Theseus versus Romulus in his "Lives" and by his own admission:
"As geographers, Sosius, crowd into the edges of their maps parts of the world which they do not know about, adding notes in the margin to the effect, that beyond this lies nothing but the sandy deserts full of wild beasts, unapproachable bogs, Scythian ice, or a frozen sea, so in this work of mine, in which I have compared the lives of the greatest men with one another, after passing through those periods which probable reasoning can reach to and real history find a footing in, I might very well say of those that are farther off: "Beyond this there is nothing but prodigies and fictions, the only inhabitants are the poets and inventors of fables; there is no credit, or certainty any farther."
Advanced ideas about atomic theory are not likely to survive down through the ages when a culture is still essentially describing the mythos of it's own origins.
2. The physical world is proof of absolutely nothing other than the existence of the physical world. In fact there are many theories about multiverse rather than universe. Science and it's laws can only be applied to our universe. We can reasonably assume that our universe is expanding into a vacuum. That is not by any means the same as saying our universe is expanding into "absolute nothingness" and what lies beyond our universe is outside the realm of any sort of scientific determination one way or another.
I am sorry but all you are presenting is a particular belief system you yourself have as accepted as fact, no better and no worse than anyone else's belief system, except you also choose to dress it in what you believe to be "science" but is not, and therefore as "fact" when it is not (in terms if something is either factual or it is not factual. What you present is possibly true, just as possibly not true. Since it cannot be presented as fact, it must necessarily be not factual).
Much like Plutarch's geographers, something I see very often when people offer "scientific proof" on Bluelight about philosophy and spirtuality, is they are taking a "map" of what they believe to be scientific knowledge, and merely use the edges to scribble in notes like "Ignorant superstition" or "Nothing" or "Infinity" and think that science has somehow proven that to be the case. The reality is often that is nothing more than a convenience to prevent having to accept the truth that the map is still limited and beyond it's edges, the map can offer no real guidance.
In this case, where the map ends at Life and Death, we can all scribble in something - reincarnation, resurrection to the kingdom of Heaven, "nothing". You are sure science proves "nothing". It has not even come close. Whatever any of us put in those margins, sorry, your notations are no more convincing than any other cartographer of the human experience.
The only absolute is "There is no credit, or certainty any farther".