Ancient mythology and black-goo in Prometheus

I would say it has its roots in ancient mythology in that it could be associated with the river and goddess Styx. The river itself is supposedly black because Demeter entered the river while mourning. Styx is also considered to be both corrosive and toxic (see Ptolemy Hephaestion, New History).

Loosely, the word 'styx' (translated from Greek 'stygos' then Latin) means hatred, abhorrent, gloomy (think: stygian night).

Styx, as noted, is both the river and the goddess. As the deity, she is the eldest of the Okeanides--daughter of Oceanus and Tethys--and a chthonian (underworld/Hades) goddess. During the Titanomachy, she sided with Zeus (all oaths to Zeus are sworn to her). As the river, Styx is both its own river as well as the marsh where the five great rivers converge in the underworld (NOTE: The Theoi project has an extensive entry on Styx).

In many contemporary stories such black-goo is representative of some form--granted usually evil--of life as in the Klyntar/Symbiotes in Spider-Man that is Venom, Armus from ST:TNG 'Skin of Evil' (who was created by the 'Titans'), or even the space-faring Goa'uld from Stargate.

How this may fit with Prometheus as a life-giving goo I would guess might come from the oath sworn to Styx: those who break it must drink from the river Styx as punishment. However, there are other myths associated with what occurs when you drink from any of the five great rivers (Styx, Lethe, Phlegethon, Acheron, and Cocytus).