Technically, calcium carbonate is insoluble in water, but all it takes is some CO2 in that water to change that. There's plenty of CO2 in our atmosphere (there's always been some, but now there's more), and that's how we end up with "acid rain" that dissolves limestone and marble. read more
Living in the State of Missouri and being surrounded by the stuff, I can easily answer this question. Approximately 65 million to 75 million years ago, this area of the country was under water. It was shallow seas, which mean the area was ripe with soft crustaceans and other coral like life forms. read more