Teru_Kage David's head and body were initially on the deck of the big cannon. The Engineers most likely did not need a suit on that planet, as shown by the free roaming Engineer at the start of the movie. It is common practice in spacesuit design to blow fresh oxygen from the back of the helmet so that it flows down over the astronaut's face. Because of constant motion of the stars in a galaxy is visible, constellations change their shape over the time.But all old civilizations' star maps and future maps are the same in the movie, even they are separated from each other by several (tens of) thousands of years.Hrithik Roshan’s incredible acting is touted to be the saving grace in this predictable dark movie.Barring Hrithik’s acting brilliance, the movie scored average by the leading film critics in India.Earlier in the movie, Shaw had no problems carrying the helmet, still with the head in it, in a bag, with one arm and still held on to it in the storm.Shaw and Ford carried the head together, hanging straight down between them in a bag with handles.In the first Alien movie, the xenomorph grew from chestburster to full size without eating any of the crew.It's possible that their physiology allows them to grow by absorbing air/water alone.
This happens inside of the lab where there is no organic matter present.
Shaw found David's head and body in the same place that they'd fallen after the Engineer attacked him.
But considering that the entire spaceship had just violently crashed, shouldn't the parts of his body been tossed all over the chamber? Located near each other is coincidence but not impossible. Besides the rooms in the Lifeboat are sealed; so oxygen can flow even with any breach in another room.
It is impossible to get any useful data from carbon dating like they do when they examine the first "engineer" body.
For carbon dating, you need to know the exact mixture of carbon isotopes and changes in it in the atmosphere of the planet for about 20,000 years.
They start running directly away from the ship as fast as they can, but in exactly the same direction in which it's falling.