ONE day, in the mid 1800s, naturalist Charles Darwin walked into a field behind his home and set upon the ground a line of coal stones. Then he waited. Over the following decades, the stones disappeared into the soil. When they had vanished, Darwin dug a trench beside them. He wanted to see if a theory he had been working on could be proved: namely, that the stones had not sunk. They had been buried.
The prevailing view at the time was that soil was disintegrated rock modified by weather. It was inert, unchanging and unchangeable. This belief was formed by a simple, but profound reality. Most of the early work on soil had been conducted by geologists because they were the ones with both the scientific method and equipment to conduct the research. But, in experiments that lasted