Here's why:

* Ripple marks are small, wave-like ridges and troughs that form on the surface of sand or sediment.

* They are created by the movement of water or wind over the sediment.

* The direction of the flow can be determined by the shape and orientation of the ripple marks.

Possible environments where ripple marks form:

* Rivers: Fast-flowing rivers create asymmetrical ripple marks where the upstream side is steeper than the downstream side.

* Beaches: Waves on the shore produce symmetrical ripple marks.

* Deserts: Wind blowing across sand dunes forms ripple marks, often large and with a different shape than water-formed ones.

* Shallow marine environments: Tides and currents can also form ripple marks in shallow water areas.

So, finding ripple marks in a sedimentary rock tells us something about the environment where the rock was formed.