Geoscience Reference
In-Depth Information
The rock cycle
At the surface the results of that heat engine beneath our feet and the solar furnace above
our heads meet and drive the rocks full circle. Mountain ranges lifted high by mantle cir-
culation and continental collisions are weathered down by solar-powered wind, rain, and
snow. Chemical processes are at work as well. Oxidation by the atmosphere and chem-
ical dissolution by acids from living organisms and dissolved gases help to break down
the rocks. Large quantities of carbon dioxide can dissolve in rainwater to make a weak
acid that causes chemical weathering, turning silicate minerals into clay. These remains are
washed back down to estuaries and oceans where they form new sediments, eventually to
be scooped up into new mountain ranges or carried back down into the mantle for deep re-
cycling. The whole process is lubricated by water incorporated into the crystal structure of
minerals. This rock cycle was first suggested in the 18th century by James Hutton, but then
he had no idea of the depths and the time scales over which it occurs.
So far we have glimpsed just the surface of our amazing planet. Now we will dig deeper
into the rocks and into time.
