Soil is not dirt. It is a complex ecosystem — minerals, organic matter, water, air, and billions of organisms per gram. It forms slowly: approximately one centimetre of topsoil takes 100 to 400 years to develop under natural conditions. It erodes much faster.
The primary cause of accelerated erosion is agriculture. Ploughing exposes soil to wind and rain. Monoculture depletes organic matter, reducing the soil's ability to hold together. Deforestation removes the root systems that anchor soil in place. Overgrazing compacts the surface and kills the vegetation that protects it. The result is that soil dissolves — into the air as dust, into the rivers as sediment — faster than it can be replaced.
The consequences are severe and accumulating. The United Nations estimates that one-third of the world's soil is moderately to highly degraded. In parts of China, the loess plateau has lost metres of topsoil. In the American Midwest, intensive agriculture has reduced organic matter by half since settlement. Globally, we are losing approximately 24 billion tonnes of fertile soil per year.
Soil erosion is dissolution without spectacle. There is no dramatic collapse, no single catastrophic event. The ground simply thins, year by year, until it can no longer support the crops that depend on it. The dissolution is slow, cumulative, and, for now, largely ignored.
In Fiction
John Steinbeck's The Grapes of Wrath (1939) is the great novel of soil dissolution. The Dust Bowl was not a natural disaster — it was the result of ploughing the prairie, removing the deep-rooted grasses that held the soil in place. When the drought came, the soil dissolved into the air. "The tractors came over the roads and into the fields," Steinbeck writes, "great crawlers moving like insects, having the incredible strength of insects." The dissolution of the soil dissolved the people who depended on it.