[Physicist]

I think they mean that the CO2 content is buffered. Calcium carbonate releases CO2 when it dissolves, so if the CO2 pressure in the ocean is lower than the partial pressure of CO2 in the atmosphere, the dissolving shells will just bring it up again.

I remember reading that the CO2 content in the deep ocean is so low that a shell dropped into the ocean will dissolve before it reaches the bottom. I don't know whether that's correct.

As for the calcium, I suppose it's just there in solution in sufficient quantity.

[JethroHathAWay]

Is it like coke?

[CobaltBlue]

So the extra carbonate in the ocean would prevent the CO2 in the atmosphere from being absorbed into the water.

And, given that CO2 is a "greenhouse gas," that would cause the atmosphere to be warmer. And also give green plants something to "breath", so that they could be food for multicellular animal-type organisms.

Makes sense to me. Seems like so much of life on earth depends on strange quirks.

We're (each of us) the descendents of countless generations of beings that actually lived long enough to reproduce! Talk about lucky! How improbable is that?