Your points are good, I just wanna further complicate it (particularly wrt stone age, virgin materials and labour)

Should very much note that the "output>input chains" that get longer through the centuries are human production chains, production chains under human management, control and understanding. The chains are predicated on the existence of the 'natural world' (the uncaught fish in ch7fn7) which is the result of millions of years of evolutions and developments and ecological relationships which even today we do not fully understand.

The supply chains' operation also destroys this 'natural world' on which it's premised; oil is limited, ore veins dry up, forests are cleared, soil is exhausted, etc. This destruction can be shifted/alleviated (e.g. from the 70s, pollution reduction in the north was aided by sending the dirtier production south; the ever increasing use of fertilizer to maintain crop yields), but is as Marx notes intrinsic to the capitalist mode of production.

One reason it is intrinsic in my opinion is that capitalism does not view 'nature' as producing value.(1) Hence, value, material generally, extracted from nature require no compensation. As Marx says in ch2, if commodities "are unwilling, [man] can use force; in other words he can take possession of them".(178) It doesn't matter if it's a rock, plant, wild donkey or anything else: if a commodity has no owner, it's "free game". Marx alludes to the fact that, women, for instance, may be commodities in ch2fn1, but the point isn't developed further here (or anywhere else in Capital, tbh. Marx dropped the ball on feminism.)

In ch2 Marx further points to the fact that, for owners of commodities to deal with each other as commodity owners, to interact through their commodities; "their guardians must...not appropriate the commodity of the other, and alienate his own, except through an act to which both parties consent. The guardians must therefore recognize each other as owners of private property."(178) Because, e.g. a tree, is not recognized as the owner of private property, as a commodity owner, a member of civil society, in a word a legal person it is therefore itself a commodity. In chapter 2, brief allusion to women-as-commodities aside, the question of what is and is not a commodity seems simply to be "is it a human or not".

In chapter 3 and 6 this is further complicated by mention of slaves, humans who are commodities. In the inverse of the conditions for the sale of labour-power we see the conditions for the sale of human beings:

"In order that [labour-power]'s possessor may sell it as a commodity, he must have it at his disposal, he must be the free proprietor of his own labour-capacity, hence of his person. He and the owner of money meet in the market, and enter into relations with each other on a footing of equality as owners of commodities, with the sole difference that one is a buyer, the other a seller; both are therefore equal in the eyes of the law." (271)

A person can thus be enslaved when they are not the legal equals. This can mean, as in e.g. absolutist France, "The Rights of Man" just don't exist, no one is equal, or it can mean, as in Yankland, that black people and natives don't count as "real" humans. Such people are, rather than being commodity-owning members of civil society, part of civilization, uncivilized. They and their property are treated as natural resources; gangs of whites can and did go about with guns in Yankland abducting black people for sale, robbing and massacring native villages and looting graves and ceremonial sites, digging up and farming medicine and hunting places, etc. This is the whole basis of primitive accumulation, which will be the focus of part 8 of the book.

The supply chains thus appear to begin (and Marx begins his analysis presuming) with extraction, but they begin earlier and endlessly circulate in and out of the sphere of 'social production' which is Marx's focus.

(1) Marx seems to sometimes think abstract human labour is physiologically and intrinsically different from animal labour (e.g. page 284 where he creates a metaphysical justification for this). I disagree, and think it weakens his argument to have such metaphysical ideas (and such metaphysical ideas obscure how capital-patriarchy labels e.g. housework as not-work and expropriates the products (reproduced labour-powers) as a natural resources.)