When most of our limestone and coal formed?

Most of the Earth's limestone formed during the Paleozoic Era, particularly in shallow marine environments, with significant deposits created during the Carboniferous period about 359 to 299 million years ago. Coal primarily formed during the Carboniferous period as well, when vast swampy forests existed, allowing for the accumulation of plant material that eventually transformed into coal over millions of years under heat and pressure. These processes collectively contributed to the substantial fossil fuel reserves we rely on today.