Soil: A Fragile Resource

Soil: A Fragile, Slowly Renewable Resource

By: Peggy Rudberg

Soil is the surface layer of Earth’s continental crust, made up of minerals, living and dead organisms, water, and air. This crust amounts to 0.05 percent of the planet’s mass. Billions of years ago, when the planet was primarily aquatic, the crust was bare rock, unable to retain water or nutrients, making it uninhabitable to life. It would take soil to enable Earth to sustain life as we know it.Soil formation begins when weathering and atmospheric compounds break down rocks into smaller mineral particles. The parent rock determines soils texture based on particle size, from gritty sand to slippery silt to sticky clay. Soils usually contain particles of all three sizes, often lying in layers. The parent rock of most U.S. soils is granite, an igneous rock largely composed of oxygen and silicon.The first organisms able to move onto Earth’s rocky crust were lichens, a symbiotic relationship between fungi and algae or cyanobacteria. The fungi could absorb and hold water, while the algae provided energy from photosynthesis. Lichens produced acids that continued to fragment rock. Plant life followed, with the help of mycorrhizae, a cooperating fungus whose filaments enhance the nutrient intake of plants. By 0.42 billion years ago vascular plants were growing on land and provided a food source, enabling more animals to migrate from the ocean.As more life forms evolved and colonized land, a food cycle between species developed. Organisms grew, fed, and decomposed. This organic matter helped stabilize and bind minerals, grouping soil particles into a structure that included a network of pores where air and water could reside. The organic matter also fed microorganisms that broke down plant and animal residue into nutrients and forms of carbon.Besides being the medium for growing crops, soil traps carbon, filters and stores water, and reduces flooding and erosion. It’s a crucial resource, and it’s renewable, but only under the right circumstances. It can take 1,000 years to form one inch of topsoil. This process is not steady; soils are created at different rates and are constantly gaining and losing components depending on climate, biota, and time. Most of today’s soils were formed less than 10,000 years ago, after the last glaciers scraped away earlier soils. By this time humans were already affecting their environment by burning, planting, and building.Today, intensive agriculture disrupts the natural cycling of nutrients by harvesting the source of compost that fertilizes the soil. Deforestation, urbanization, contamination, erosion, desertification, and over-fertilization also threaten our soil. It is critical that we protect our existing land from further depletion and follow sustainable resource management in agriculture. Our lives depend on it.References:BBC, One amazing substance allowed life to thrive on land, by Claire AsherScientific American, Evolution of Earth, by Claude J. Allgre and Stephen H. SchneiderUniversity of Hawai’i at Manoa, Soil Formation