The atmosphere is composed of 71% of nitrogen, 3% carbon monoxide, 23% oxygen and traces of argon gas. The air on LV-223 is mostly identical to Earth's atmosphere, but contains poisonous levels of carbon monoxide (CO) making it impossible for humans to breathe outside. (Earth levels average about 0.00001% for comparison).
It is uncertain if there were any existing life forms, before the Engineers, but at some point, a group of Engineers put up an outpost on the planet. It is speculated by Janek that it was some sort of military base set up by the Engineers to build biological weapons before they lost control of them. There are Worm-like life forms within the domes but it is unknown if they are native or foreign. These beings eventually go through a mutation process similar to Fifield's and become the lethal Hammerpede.
At some point approximately 2,000 years before, the Engineers established a temple on LV-223 and initiated a plan to wipe out humanity for reasons unknown by releasing a pathological agent known as A0-3959x.91 – 15. However, they apparently lost control of the pathogen and led the Engineers there to die off. Four surviving Engineers took refuge within their ship's Hypersleep Chambers, only one of them survived.
In 2089, archeologists Elizabeth Shaw and Charlie Holloway discover a star map among several unconnected ancient cultures within a cave during their expedition on the Isle of Skye. They interpret this as an invitation from the Engineers. Shaw then contacted Peter Weyland, the elderly CEO of Weyland Corporation, for a proposal in order to gain enough funding for an expedition to follow the star map. Weyland agrees with the proposal and funds the creation of the scientific vessel Prometheus to follow the map that led them to LV-223.
In 2093, after the Prometheus' two year voyage, the ship arrived on LV-223. The Prometheus crew explored the moon's surface where they came across the Engineer's structure. The crew entered the structure and discovered the bodies of some Engineers, as well as several "urns" stored within the structure. The crew's interference caused the pathogen stored within the "urns" to melt, A few crew members were exposed to the pathogen, and in the ensuing chaos most were killed. The android David successfully found the last living Engineer and informed Weyland, who was secretly aboard the ship the entire time. Weyland and his team went to the Engineers' ship to commune with the last Engineer however, upon waking; the Engineer decapitated David after a brief conversation and killed Weyland along with the entire party, save Shaw, who managed to escape.
The Engineer reactivated his ship and headed for Earth to carry out his original mission to wipe out the human race. The remaining crew later sacrificed themselves and the Prometheus to destroy the Engineer's ship. The Engineer survived and attacked Shaw within Prometheus' lifeboat, Shaw released the Trilobite she had extracted earlier from her womb as the result of having sex with Holloway who was infected by the pathogen, which restrains and impregnates the Engineer while Shaw escapes. Shaw recovers David's remains from the crashed Engineer ship, the two activate another Engineer ship and leave LV-223 for the Engineer Homeworld. In the crashed lifeboat, the impregnated Engineer died, birthing a Deacon.