Thats not Earth at the beginning and what the Skeleton Head in the Rocks Means.

Since the Mrs was watching Magic Mike with the ladies, I took in Prometheus for a third time. Here are my new observations. First, the planet at the start of the film is not Earth. It cannot be as it would have to have been nearly a Billion years ago as the fossil records shows life on earth in the form of Dinosaaurs millions of years ago, sure it could be post dinosaurs when man emerged, but when the ship comes in for landing, the geoscape aside from the waterfall of LV 233 looks alot like what we see at the film in parts, there is a desert yes, but also snow covered peaks and lava fields hardened. Now the Skull in the mountain, easy enough. What do we mark poison and dangerous stuff with? A skull and crossbones. This is how they marked what were the deadly silos. Death is here. We know from Alien they placed a warning beacon to tell people danger was present, same thing.