He was definitely seeding life. This has been stated clearly by Ridley himself and is quite obvious given that the planet appears to be in its formative stages with only minimal plant life.
A pre-vis on the blu-ray actually shows a very primitive amphibian creature crawl out of the water and onto land after the DNA sequence.
Our oldest ancestor, LOL.
My personal belief is that this is NOTnot the BLACK GOOblack goo, this was probably millions of years ago, and the effects are completely different than those of the BLACK GOOblack goo. It also looks different.
Another scene on the blu-ray shows Ridley designing the SACRIFICIAL GOOsacrificial goo with various berries and coloured honeycomb mashed into a bowl. If it was the BLACK GOOblack goo, he would have simply made it BLACK!!! ITS NOT EVEN BLACK PEOPLE!!black. It's not even black, people.
- Phase one: create people
- Phase two: force evolutionary change with Xenomorph DNA or "BLACK GOO""black goo"
The only question remaining about Prometheus Prometheus (originally titled Alien EngineersAlien Engineers) is why they would want Xenomorphs. Weapon? Cleansing a planet like a Petri dish?