Ah, pedology is a very detailed arm of the "Earth Sciences." Soil is defined by geologists as "earth material that has so modified and acted upon by physical, chemical, and biologic agents that it will support rooted plants. The term is used by engineers includes, in addition to the above, all regolith". (Dictionary of Geologic Terms, revised edition,American Geologic Institute, Anchor books, 1976, ISBN 0-385-08452-8).

So, while geologists like to see evidence of biologic activity before we call it soil, engineers call all of the surface material, no matter what horizon (layers of soil development) as soil. Probably why the surface deposits on Mars are often called soils.

My geologic dictionary does not have a definition of "dirt", nor of "earth" in this context. However, there are such things as "dirty coal", indicating a contaminated, or non-pure state.

"Unearth" has basically two definitions, to dig up, or to bring to light, expose.

Inhabitants of Mars might have new definitions...as they would be, in truth, "Un-earthed".

(Here's a soil characterization field guide, just to show a glimpse of the complexity of soil science)