[iwwr]

Actually, the biggest deposits of CO2 on Earth are in the form of carbonate rocks. If that CO2 were to be released from the rock, we'd have about 90 atmospheres of pressure just from that alone, like on Venus. To the point where today CO2 is just a trace gas in the Earth's atmosphere.

Starting early in Earth's history more CO2 got dissolved in the primordial ocean and locked down than what got released by other processes such as volcanism or plate tectonics.