When the earth turns to dust

The number of organisms living in a handful of soil outnumber all humans on the planet. They ensure that the humus layer stores nutrients and water. After oceans, soils represent the planet's largest carbon bank. Soils store more carbon than all the world's forests combined.

As cities around the world expand, fertile land is disappearing under concrete and asphalt. Microorganisms are suffocated under this artificial surface, and above it rainwater flows away rather than seeping into the soil.

Like human skin, the Earth's sensitive surface needs protection from the sun, wind and cold. Large areas can dry out, and ploughing can dislodge the top layer so that it is blown away by the wind.

Depletion of the soil through deforestation, over-fertilization and overgrazing can turn land into desert. Climatic factors like drought become a catalyst in a chain reaction - that is set in motion by human activity.

Monoculture plantations need large amounts of fertilizer and pesticides to remain productive. Some types of pesticides also harm the natural soil biota, reducing the soil's fertility.

Whether resulting from industrial leakage, disaster or weapons, or from years of over-fertilization: once soil is contaminated, fixing the damage is costly and time-consuming. According to official sources in China, nearly one-fifth of agricultural land there is contaminated.

The earth is also dug up to get to raw materials. This photo from Germany shows how brown coal mining strips away the topsoil. Through resource extraction, land that could provide wildlife habitat, or be used for agriculture or human habitation, is lost.

It takes 2,000 years for nature to produce a 10-centimeter (4-inch) layer of fertile soil that holds water and nutrients, and where plants can grow. To protect fertile soils worldwide, the United Nations has declared 2015 International Year of Soils.