I understand what water and air are composed of and I more or less understand how fire works. But what is soil? If you put your hands in your garden, you will take out very heterogenous stuff, you will get some twigs and bugs which of course are organic matter, but what’s the general brown stuff? Is it organic? Were does it come from and how is it produced? Also collateral question, if earth is organic matter, when the first living organisms came out of the ocean, which were plants, how did they find nutrients?
In: Planetary Science
It’s mostly minerals. Scientists put them into seven different categories depending on their size.
Boulder, cobble, pebble, gravel, sand, silt, clay. From boulder to gravel, they are considered different sizes of rocks. Over long periods of time, wind and rain break down larger minerals into smaller ones. You can actually see evidence of this on mountains. Frequently, one side of a mountain will get lots of rain and it is covered in soil and vegetation, while the other side gets less rain and the ground is much more rocky there.
Sand, silt and clay are what make up soil. Chemically, a clay or silt particle is made up of the same stuff that rocks are made of, but because they are so small, they interact differently with water. Soils are classified by the ratio of those three major components.
Soil usually also has a bunch of organic matter in it, somewhere between 1-10% is pretty normal. Besides twigs and bugs, a lot of it is stuff that is decaying and a lot of it is bacteria. Soil with a black color to it usually contains a lot of organic matter.
Finally, there’s a bunch of water. Even when it hasn’t rained for a while, there is still moisture filling up the spaces in between particles of clay and silt.
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