Hi, I'm Craig. I'm a dirty dirty man and this is Mental Floss on YouTube. Today I'm gonna answer Caleigh Waddell's big question: What is dirt made out of? Well Caleigh, not to get all know it all on you but I'm going to assume you mean soil instead of dirt. Soil is the top layer of the earth where plants can grow. Most people use dirt and soil interchangeably but scientists don't consider them synonyms. Dirt is the loose soil so it's no longer a part of that layer and no longer supporting plant life. Plus it can refer to a whole mess of other things. Get it? Now that we have that all figured out, let's get dirty. Started.

(Intro)

So soil is formed when rocks underground come in contact with water, like rain water, or when I pour one out for my homies. Over time those rocks break down into smaller minerals like quartz, mica and calcite. As organic material breaks down it also contributes to soil formation. Around 45% of the soil that's formed is made from three main properties: sand, silt and clay. 25% is water, 25% is air and 5% is miscellaneous organic material like plant debris.

But what are all of those things made out of you ask? As for chemical elements, oxygen is extremely abundant in soil. Some other elements commonly found are phosphorous, nitrogen, potassium, silicon, aluminum, iron, calcium, magnesium, sulfur, sodium, and that gopher from Caddyshack.

I'm sure you've noticed that I'm being pretty vague about this. That's because soil differs from place to place. It's not always the same which means it probably doesn't always consist of the same stuff. In the United States alone, there are around 50,000 different types of soil and that's just in my laundry basket. These differences are due to five factors: climate, parent material, topography, organisms and time. All of that in my laundry basket. Basically soil in the tundra is going to be different from soil in the desert which is gonna be different from soil in the prairie which is gonna be different from soil in... Costco.

One interesting way to examine how soil varies is by looking at the soils's pH which helps determine which plants will thrive in that soil. pH is greatly affected by things like climate and rainfall. Soils with low pH tend to have less macronutrients while soils with high pH tend to have less micronutrients. In the Western US, soil is more alkaline whereas on the East Coast and in the Pacific North West it's more acidic. So if you're especially curious about the soil in your area, one way to find out more is to pH test it or phhhh test it. You can buy soil testing kits for pretty cheap at a hardware store. In addition to pH levels, many of these will tell you how much nitrogen, phosphorous or potassium is in the soil. Another good way to test out the soil is to roll around in it.

Thanks for watching Mental Floss on YouTube made with the help of these filthy filthy people. If you have a question of your own, leave it in the comments. I will see you next week. Hopefully after I've showered after rolling around in the dirt. The soil.