Throw up some confetti because it’s the start of something new! This week marks the beginning of a new series—10 Things You Didn’t Know—in which I list 10 factoids you didn’t know you wanted to know about a science topic, concept, or occurrence. This week it’s all about that wonderful stuff beneath your feet: soil.

1. Soil is composed of minerals and organic matter

Soil texture triangle
Mineral soils are made of particles of varying size. In order from large to small the particles are sand, silt, and clay. Soil scientists use soil texture triangles to find the percentages of sand, silt, and clay in a soil to determine soil type.

2. Soil is alive

Microbes, fungus, insects, nematodes and other living organisms in soil break down organic matter (leaves, grass, etc.) to produces nutrients in soil that are essential to plants…because they crave more than electrolytes. That last part was a movie reference.

3. “Dirt” is a bad word

Most people use dirt as a catch-all term for the stuff on the ground. However, to professionals, the term “dirt” refers to soil that is devoid of nutrients, life, and organic matter. It’s a generalization that implies an insult akin to saying a person is dead inside and has no soul.

4. Your skin isn’t the only thing that has pores

In between soil particles are spaces—referred to as pore spaces—that contain air, water, and nutrients. Large particles = large pore spaces. Small particles = small pore spaces. It’s from these pore spaces that plant roots get water, nutrients, and air.

Bonus: I made a video about this in grad school because who wouldn’t want to make a video in lieu of writing a paper?

5. There are more microbes in a teaspoon of soil than there are people on the earth

Yep. The bacteria, fungi, protozoa, nematodes, earthworms, and insects found in soil are very small (microscopic in some cases), so there can be a large number of them in a small amount of soil.

6. That “earthy” smell is caused by bacteria

Actinomycetes release a compound called geosmin whenever soil is disturbed. The smell, also known as petrichor, is associated with rain and spring because soil microbes are more active during spring, it rains more during spring, and rain disturbs soil causing the odor to be released.

Bonus: Science Friday had a very good segment on this and other topics related to this post.

7. Soil type is an identifying feature of wetlands 

Wetlands at Congaree National Park
Hydric soils (“hydro-” means water) have soil pores that are saturated with water permanently or most of the time. The lack of air causes anaerobic microbial and chemical processes that result in colors and smells only found in hydric soils. When wetland delineators are looking for the edge of a wetland, they look for hydric soils that indicate where a dominant presence of water begins.

8. Clay particles are flat

While sand and silt are rounded (to some degree) broken down rocks, clay is made of a flat crystalline structure.

9. Cat litter is basically clay

Clumping clay cat litter primarily consists of bentonite clay, which has a shrink-swell properties that cause it to expand when wet and shrink when dried. Because of those abilities, it’s ideal for turning liquid into solid clumps when the clay dries.

10. Soil quality affects all of us

Healthy soil plays a large role in agriculture and is important because we all need to eat. Plants don’t grow well in dirt. Loose dirt washes into waterways when it rains and causes poor water quality. Loose dirt in water—called sediment—can clog fish gills. No farms, no swimming, no fishing? That’s no good.

Image credits: Soil texture triangle – Natural Resources Conservation Service; Congaree wetlands – Chenille Williams

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