Yet soil loss is not just ancient history. When I compiled data from around the world on the rate of erosion from agricultural fields to compare with data on the pace of soil production, I found that tilled soils erode 10 to 100 times faster than soil forms. Every year, about half a percent of the world's arable land is degraded enough to be taken out of production.

While the pace of soil erosion makes it challenging to prioritize soil conservation efforts, thick loess soils can maintain agricultural productivity for longer than can thin soils developed in place from rock weathering. In all likelihood, North America will be feeding the world for the foreseeable future because of its natural endowment of loess.

With a limited – and shrinking – global amount of highly productive cropland, the future of humanity hinges on whether we take care of the world's best soils. What do we need to do in order to feed the world well into the future? Sustain both the physical body of the soil (prevent erosion) and the fertility of the soil. It would help to rebuild soil fertility on degraded and marginal agricultural land. How we will do all this in the coming post-cheap-oil world is a question deserving far more attention than it’s getting.

You don't have to be a geologist to realize that a century is not much time in the life of the land. And the health of the land has always been at the heart of the health of human societies. Fortunately, agriculture can also rebuild soils far faster than nature does. But to motivate doing so on a continental scale, we need to see North America's rich endowment of fine agricultural soil as an intergenerational global trust because, like us, people tomorrow will need to eat. In the end, it really is that simple.


David R. Montgomery is a professor of geomorphology at the University of Washington. He is author of Dirt: the erosion of civilizations and The rocks don't lie: A geologist investigates Noah's flood