[Rightwing Conspiratr1]

But Venus has a very thick atmosphere with a high surface pressure (~ 96 atms). In order for ejecta to escape the planet, they must have very high energies when they are removed from the surface, such that by the time they have traversed the atmosphere, the ejecta still have sufficient velocity to escape.

So how do they know what Venus's atmosphere was like 2 billion years ago?

[RitchieAprile]

here’s some light reading..

http://www.britannica.com/EBchecked/topic/625665/Venus/54178/The-atmosphere