To illustrate the amount of soil on Earth.

Pretend that an apple is the planet Earth, round, beautiful, and full of good things. Notice its skin, hugging and protecting the surface, Water covers approximately 75% of the surface. Cut the apple in quarters. Put three quarters (75%) aside.
The three quarters (75%) you just removed represents how much of the earth is covered with water (oceans, lakes, rivers, streams). What is left (25%) represents the dry land. 50% of that dry land is desert, polar or mountainous regions, where it is to hot, to cold or to high to be productive.
So cut that dry land quarter in half.
When 50% is removed this is what is left 12.5% of the original. Of that 12.5%, 40% is severely limited by terrain, fertility or excessive rainfall. It is to rocky, steep, shallow, poor or to wet to support food production.
Cut that 40% portion away. You are left with 10% of the apple. Now peel the skin from the tiny remaining sliver.
The remaining 10% (approximately, there is difficulty within the scientific community in coming up with an exact figure)- this small fragment of the land area represents the soil we depend on for the worlds food supply. This fragment competes with all other needs, housing, cities, schools, hospitals, shopping centres, lands fills, etc.
Courtesy of: The Natural Resources Conservation Service, Syracuse, NY, U.S. Department of Agriculture.

Soil is Inter-Disciplinary