Riddle

What measures out time until in time all is smashed to it?

Choose an answer

A.Rust
B.Erosion
C.Dust
D.Sand
Hint: It's a word with 4 letters, starting with "S".

Answer

Sand

Why this is the answer

An hourglass uses falling sand to measure time, and over enough time rocks and everything else erode down into sand.

This riddle is filed under Hard/Difficult Riddles and rated Medium.