OK peeps, this is a list of some compiled theories. These are NOT my own theories. Theories that are made by A FANDOM User are unmarked.
1. Fishrus: Precursors use teleporters made by precursors to help them go biome to biome. The ones marked will also be where the juveniles end up.
2. Warpers are genetically engineered Precursors - an extreme solution to an extreme problem; What cyborgs are to humans, Warpers are to Precursors.
3. Marty1233223: I think the dead zone crater is a bomb site from where the first traces of the carar were found by the precursors and the tried to destroy it with a bomb
4. BippityBop: Kharaa isn't from this planet.
4 Theories by Zadagr:
5. Reaper Leviathans were not indigenous to the surface and either the radiation of the Aurora mutated the or the crash released them from somewhere deeper.
6. Subnautica is a prequel to Natural Selection, which was made by the same developers. This is supported by the name of the infection in both games being Kharaa in the full release while it was originally Carar in Subnautica. Another reason for this theory is that the Tiger Plants in Subnautica bear a striking resemblance to the Hydras in Natural Selection. Additionally, they are certainly in the same universe because of mentions of phase gates and gorges in Subnautica and mentions of Altera in Natural Selection. The reason it is a prequel is that even though you get cured in the end something you bring might still be infected like a bottle of water and the bacteria is only on this planet and the quarantine enforcement platform has prevented the bacteria's escape.
7. The precursors created the Warpers out of other things on the planet in order to slow the bacteria and prevent its escape from the planet.
8. The reason the precursors are no longer around is that they all got infected, destroyed their physical bodies and stored their minds in the alien sanctuaries that can be found around the map. This is supported by the data found in the sanctuaries discussing incredibly complex data from biological origin. Another sanctuary describes the life of one precursor individual that at the end says that they were stored in sanctuary 3 and their corporeal body was destroyed.
I hope you liked this!