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 dead diatoms that sink to the bottom of a body of water. Diatoms have cells that are enclosed within silica skeletons. That's probably the "white powder" the question is asking for.