I've been claiming for a long time that the Earth's atmosphere would have been a lot more like Venus without an event like this one that removed most of it. For the same reason, we won't be able to turn Earth back into Venus, no matter how much carbon we burn.

--interesting and important claim, if true. But it might have worked the opposite way,e.g. the collision released more gases causing the Earth atmosphere to become larger, not smaller. I have no idea; I'm just asking if this "claim" can be backed up somehow.