[Buggman]

Okay, now let's extrapolate backwards: Venus' atmosphere today is (IIRC) already thicker than Earth's even with the solar wind damage, so what was it like, say, a few million years ago?

Either Venus was once a gas giant, or something's not adding up here.

[Calvin Locke]

Venus' atmosphere today is (IIRC) already thicker than Earth's even with the solar wind damage,

Try around 90 Earth atmospheres at the surface.

That's like being 3000ft underwater.

[Tarpon]

The key is the magnetosphere, it protects the atmosphere. Without it, the suns energy hits the planet with no attenuation. Sun tans come quick, and it’s terribly hot.

Hydrogen, Helium and Oxygen, what would be higher up in the atmoshpere would suffer the brunt of the solar winds stripping action. This is what ESA measured. So what remains of the atmosphere would be ‘heavy’, which is appears to be.

All we know for sure is what we measure with our instruments, since no one has been there to do soil and rock studies.

Venus is about the same age as Earth, 4.5 Billion years old.