Which is greater — the number of organisms in a handful of healthy soil or the number of people on Earth? If you said organisms, you are correct! Know some more dirt on soil? Take this quiz to see how well you are grounded on the world beneath your feet. Answers are below.

Match the number to its soil fact:

1. Number of soil classifications in the United States.
2. The top 6 inches of an acre of soil contains this many pounds of living matter.
3. Varieties of bacteria in one gram of soil.
4. Number of years it takes to create an inch of topsoil (the organic layer of surface soil which contains most of plants’ roots).
5. Gallons of water when 1 inch of rain falls on 1 acre of soil.
6. Percent of water on Earth that is contained in soil.
7. Soil needs this many gallons of water to grow one bushel of corn.
8. Percent of Earth’s carbon dioxide emissions sequestered in soil.

A. 01
B. 10
C. 500
D. 4,000
E. 5,000
F. 27,154
G. 20,000
H. 70,000

9. Soil is made up of air, minerals, organic matter and water. Excluding drought or flood conditions, what is the ideal average percentage of each of these components?

Organic matter

A. 5 percent
B. 25 percent
C. 25 percent
D. 45 percent



1. H; 2. F; 3. E; 4. C; 5. G; 6. A; 7. D; 8. B 
9. Air = 25 percent; Minerals = 45 percent; Organic Matter = 5 percent; Water = 25 percent