Johannes,

You really need to go to a public library and read some basic books about the Solar system. A lot of your questions are glaring admissions that you know nothing about the topic.

It's barely worth telling the answer to any question since you don't appear to understand enough about physics to understand the answer, and you just go and ask another dumb question in return.

My advice is that you do the reading I mention above, also look up lost of NASA resources on the Internet, and then lurk more and ask less...

Regarding CO2, the response time of CO2 transformation to carbonate is a few tens of million years for an entire planet's supply.

The time elapsed between the formation of the Earth (4.6 BILLION years ago) and the time of the dinosaurs (300 million years ago) is 4.3 BILLION years.

No anomalous CO2, no funny atmosphere, no bouyancy. (did you know we have samples of the dinosaur's atmosphere trapped in bubbles in amber?)