Be careful when reading comments like this about ages of the rocks on Mars. What is dated is the *Surface*, not the body of the rock. So, for instance, a rock formation could have been formed 2 or 3 BILLION years ago and then in the last few hundred million years become exposed to wind and weathering. It's SURFACE age would be at best the age of exposure, and often less, since the process of erosion strips craters away.

For soft and easily erodible deposits like the MFF, the surface age is very young, because they are actively wearing away.

If they were NOT 2-3 km thick, they would have to have been emplaced quite recently, in order to survive today. because they are so thick, they may be quite old (1 or 2 Billion years, or even more - Late Hesperian to Early Amazonian).

OTOH, as the article discusses, they may not actually be "rock". They might be deposits of frozen volatiles (dominantly H2O ice or clathrate), or some strange mineral deposit like the crater-filling sulphates.

Mars is a strange place, and Earth does not have a full range of analogues.