A little off topic but just so you know, lime is CaCO3. That is one calcium, one carbon, and three oxygen. Just having a bunch of CO2 around doesn't make limestone. Also, limestone is one of the best places to find marine fossils and we can watch marine animals making limestone today. The conclusion is that most limestone comes from marine animals especially in limestone formations where you can point at a spot in the rock and always be pointing at a fossil.
Google around for 'fossiliferous limestone' to see what I mean.
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