Post 6 hits the nail on the head. If you look at total carbon - the atmosphere is 1, the oceans are around 50, and the carbonate rocks are about 250. When the oceans start to get too acidic limestone is deposited on the bottom of the ocean by a very complicated clay mineral process. The ocean botton is then subducted and the limestone appears on the Earth’s surface in about 250 million years where it starts to decompose and start the cycle again. The oceans are pretty good at taking core of themselves. Also note if you ever get too hungry you can pick up a piece of limestone and extract the carbon from it and assemble some proteins. If you are smart enough, you will never starve.
You just flunked “Earth Science” class.
By some stroke of luck we have these living things called plants that can do that for us, and we don't even have to be all that smart to take advantage of it.