Limestone is made from the shells of marine organisms, primarily tiny sea creatures called foraminifera and coccolithophores.

Here's a breakdown:

* Foraminifera: These are single-celled organisms with hard shells made of calcium carbonate.

* Coccolithophores: These are also single-celled organisms, and their shells are made of tiny plates of calcium carbonate called coccoliths.

These tiny organisms accumulate on the ocean floor over millions of years, eventually forming thick layers of sediment. This sediment gets compressed and cemented together, forming limestone.

So, the next time you see a piece of limestone, remember that it's a monument to countless tiny creatures that lived long ago!