Why Engineers create the atmosphere?

These are all questions we have no answer to. We can theorize all day but it all comes down to the fact that we have no idea. Could the engineer breath the planets atmosphere? How long can an engineer hold his breath? What is the native atmosphere of the Engineers home world? Similar to earth or this moon? If he had to hold his breath, how far away from the juggernaut was the lifeboat? Why were they terraforming? Had they already already been almost complete with the terraforming and something went wrong involving an outbreak? We're they just starting the process when when something went wrong? Why is the atmosphere in the ship like Earth and better? Another thing I saw someone asking, why were the engineers in the hologram wearing suits and the ones in the "control room/navigation room" not wearing suits? Well if you go back and look at the scene. Upon entering that control room you can clearly see 4 suits kind of "hanging up" as if they had taken them off upon entering. So that answers that question right there.

THere was a suggestion that the atmosphere generation was design so that humans, if and when they arrived on this moon, would be able to survive in somewhat hostile world. I sort of like that 'welcome center' approach. What ggod would it be to invite a guest and then kill them off or at the least discourage them from finding out more. Still there muist be more to the presence of humans to start a new atmosphere just for the humans. No I think that when humans presented themselves in the pyramid that a whole series of plans were put into effect. The fact that David was able to move pretty quickly to find the Last Engineer and at least prevent hiom from getting out of the pod too early , before weyland was brought into the picture. And this just one pyramid. Maybe the Creators had the other pyramids designed for other speies scattered around their world that would eventually find their way to this moon. It could be that we were the last species and as a result we , as a species, failed the test and doomed for extinction.

The atmosphere, according to Ford and confirmed by Holloway, has only 3% CO2. Humans have no problems surviving under these measurements. This has been mentioned many times.

Yes the atmosphere has been mentioned many times as being relatively safe. And yet everyscene with the crew in trasnsit shows them with their helmets on. The one scene i didn't see helmets was the last trip to the pyramids where there is jump cut from the inside of the prometheus to the tunnels, There they remove the helmets. It may be safe but not safe enough for crew members to bet their lives on. But it is curious that the engineers and humans can share the same air. It makes me wonder if the Juggernaut's pilot seat would be equiped to let a human suit up so to speak. That would solve any potential travel needs for air.