Maybe intention was not to clear smaller species. Happenings from Prometheus occurred 24.12.-25.12. and sending black goo to Earth was planed 2000 years before

Maybe intention was not to clear smaller species. Happenings from Prometheus occurred 24.12.-25.12. and sending black goo to Earth was planed 2000 years before Prometheus has landed which implies some connection with Christianity and Jesus. Maybe they planed to send black goo as a punishment for humans.