At the time of writing NASA scientists are eagerly awaiting the results of soil sampling from their latest Martian probe Phoenix. Crucial to that experiment is confirmation of the presence of water. That precious substance essential to all life both here on Earth and maybe elsewhere. It also plays a big part in shaping the world geologically and meteorologically both here and possibly on Mars. What more natural a substance to choose for defining a unit of mass as was the case originally with the metric system.
The gram came into being as the mass of a cubic centimetre of liquid water (under normal terrestrial conditions of course) and for a time was adequate to meet the technological and scientific as well as ordinary commercial needs of the day. But even with the much more stable and precise reference used nowadays in the form of a metal prototype the difference between a litre of pure liquid water and the kilogram is immeasurable by most ordinary standards.
Much the same can be said of the origin of the metre. That 10 000 km quadrant of the Earth is still so close that it remains useful in visualising or estimating international distances.
In contrast, imperial measures have an obscure origin and a poor relationship to anything that perisists in the natural world. The pound weight owes its name to the fact that it equated to a pounds worth of coinage of a type that no longer exists. Linear measures, although they ostensibly relate to parts of the body, hardly constituted a meaningful reference even at the time of their invention, given the wide ranges of human stature.
By comparison with metric, imperial measures are abstract, ephemeral and archaic. Whatever the future may hold for systems of measurement one can at least say the Earth and water will remain meaningful to us for generations to come.