How SJ becomes Fossilised??

I would have thought that an explanation is given in the film Prometheus. Something (another threads discussion) caused a mass exodus of Engineers from Planet LV233 around 2000 years ago. At least one Engineer escaped LV233 in a space craft and either became impregnated (or already was) by the DNA changing substance or Hugger. Either after landing on LV426 or during flight the Xeno bust through the Engineers body and bio suit killing it. This Xeno made its way to the bowels of the ship (or egg silo beneath the landed ship), became an egg layer, layed the eggs and either left or died of old age. As the ship was somewhat open to the elements of LV426 all organics would surely simply dehydrate rather than decay (as there are no known microbes on LV426 to cause rotting), hense would look "Fossilised" 2000 years later Nostromo is awaken by the beacon. I dont know why there is so much conjecture re time travel and alternate ideas as this would also answer the question as to why the company would have been so secretive in sending the Nostromo to investigate, making it seem like the on board computer picked up the signal, already knowing what it could be as per the disastrous actions some years earlier. I imagine that with so many Scientists dead the government of the day would want answers and Weyland would need to tread carefully in future endeavours. Brego.