There are more microorganisms in a teaspoon of soil than people on Earth.
Why it is true
Millions of species and billions of organisms — bacteria, algae, microscopic insects, earthworms, fungi — represent the greatest concentration of biomass on the planet.
Source: US Department of Agriculture
Would you rather be asked first?
This is the reading side of the site, so the answer is in the sentence above — that is the whole point of it. Test yourself works the other way round: the question comes on its own, and the fact and the explanation only appear once you have answered.