Finding out about the past (archaeology) always involves digging down? Does this mean that the planet we live on is actually expanding? If you think about the programs on the TV! E.G. Time team, they are always digging down to find our (the planets) past. Now considering the above, Can we explain all this extra matter being added to are planet by cosmic dust? If so what was the circumference/radius of our planet when the evident meteor impact destroyed the Dinosaurs? Also at the time would it not be logical that the gravity holding the atmosphere to our planet would favour the heavy gasses? E.G. Oxygen!? Resulting in a thin layer of gas that our ancestors the mammals could take advantage of? Just a Thought.