Many limestone-forming environments are active on Earth today. Most of them are found in shallow parts of the ocean between 30 degrees north latitude and 30 degrees south latitude.

Limestone is forming in the Caribbean Sea, Indian Ocean, Persian Gulf, Gulf of Mexico, around Pacific Ocean islands, and within the Indonesian archipelago.

One of these areas is the Bahamas Platform, located in the Atlantic Ocean about 100 miles southeast of southern Florida (see satellite image). There, abundant corals, shellfish, algae, and other organisms produce vast amounts of calcium carbonate skeletal debris and fecal matter that completely blanket the platform. This is producing an extensive deposit of calcium carbonate sediment that has already converted to limestone at depth.