The last place on earth...

We don't have good pictures of could be mapped using a clock. But not just any clock - atomic clocks that are really, really, accurate. The same technology that tells us when to turn on the expressway (GPS depends on accurate timing) can react to all kinds of hidden stimuli.

By looking at the things that upset clocks, it's possible to map factors like magnetic fields and gravity variation. "Environmental conditions can make the ticking rate vary slightly," says O'Brian.

That means passing a precise clock over different landscapes yields different gravity offsets, which could be used to map the presence of oil, liquid magma or water underground. NIST, in short, is building the first dowsing rod that works.

On a moving ship, such a clock would change rate with the shape of the ocean floor, and even the density of the earth beneath. On a volcano, it would change with the moving and vibrating of magma within. Scientists using maps of these variations could differentiate salt and freshwater, and perhaps eventually predict eruptions, earthquakes or other natural events from the variations in gravity under the surface of the planet. [More]

The implications are considerable for ag - especially as water issues continue to grow. Being able to accurately map under our feet like radar watches the weather would change water law and eliminate dry holes.

We might find more oil, for example. Or realize we have less to burn.

And maybe I could get a good well.