Question

Where oceans once existed on the Earth, geological layers of ocean deposits are all that are left. What is "diatomaceous earth" and what abrasive white powder makes up 90% of its composition?

Answer 1

Diatomaceous earth is made up of the remains of diatoms, protists that belong to the eukaryote supergroup Radiolaria. Not sure about the abrasive white powder, but they're made mostly of silica, so it's likely referring to that.