A staggering 100 quadrillion (10^15) tons of the carbon present on earth is in the form of carbonate, a four-atom, planar cluster of one carbon and three oxygen atoms. Because carbon chose to bond with three rather than four other atomic partners, a carbonate forms a planar structure much like graphite.

We know these carbonates by more familiar terms: Limestone, dolomite, marble, and baking soda. As far as earthbound carbon goes, this is its preferred resting state as the vast majority of earthbound carbon is in the carbonate form. And concrete! Concrete would not exist if there was no limestone. The next time you see any structure made out of concrete just think: CO3.