a particle from outer space

A shuttle could be, in theory but it is much more likely to be hit by a micrometeorite.

It depends what you mean by dirt and gravel. On Earth much of the weathering which produces them depends on water. There is no nutrient rich equivalent of soil, nor water-rounded pebbles, but there is dust and breccia. (Breccia is composed of small fragments of broken rock), both of which probably result from micrometeorite impact.

Soil is actually a bit misleading when discussing the moon's samples. The word soil implies moisture and other organic molecules and organisms. The lunar surface is actually covered in what is called regolith. The Lunar Regolith is made up almost completely of pulverized rock from meteorite and micrometeorite impacts.

The type of rock it is, the approximate age of it, evidence of micrometeorite bombardment - or lack of it, trace elements, and dozens of other things can all be told in the "story of the rocks". All of it advances our knowledge of our nearest neighbor, as well as our knowledge of the early solar system itself.