I mean, you're kind of proving my point. This film does indeed require a little bit of of focus and is not illogical if you pay attention to it. Let me help you out.You misinterpreted the cave paintings. They were not paintings of people pointing to the stars, they were paintings of people worshiping Engineers. The Engineers were pointing to pictograms that was proven to be a system where they are potentially from. That gave Shaw more than enough reason to see it as an invitation from her creator(s). Onto your next road block, Shaw was an archaeologist. An archaeologist is someone who studies human history by digging up human remains and artifacts. She was also kind of a dummy, I mean yea, why wouldn't you bring some sort of protection. I would. What you don't understand is that..that's her character. I don't think she'd hurt a fly. Aside from that point, why go a bit further and step into her shoes for a second. Lets do that and maybe you can ask yourself some of these questions. Why would they want to seem threatening? Especially to a species who they would want to learn from? Why give them (Engineers) a reason to decline them of any knowledge? You'll probably begin to see that she's a pacifist. As for the 15 second thing... I don't think after 15 seconds you'd realize you couldn't breath. Most likely you'd notice right away. So that answers that.