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
Dead things and poop, mostly.
The exact mix will depend on your location, but a lot of it will be plant matter. Those twigs you found used to have leaves on them. The leaves were eaten by bugs or fungus, and the bugs and fungus pooped out soil. Worm poop (“casings”) is especially good for growing things. And then the bugs, worms and fungus die and other things eat those. Circle of life.
There will likely be some sand or clay mixed in. But all of the nutrients that make plants grow are generally dead things and poop.
soil is a mix of decomposing plants and animal matter, throw in some dust and perhaps clay or sand.
soil you buy in a package from a hardware store has microbes in it which is why you should handle it with gloves and wear a facemask. It may also have chemicals added to it as nutrients to grow plants in, and sometimes water crystals too
Soil is a mixture of a number of things,
– organic matter: dead/decaying plants and animal parts, waste from animals (i.e. worm poop), etc.
– mineral matter: various compounds including elements such as iron, calcium, potassium, magnesium, silica, etc. Quartz for example is SiO4. Calcium phosphate (calcium, phosphorus, and oxygen) is another common one.
– organisms: various plants, animals, fungi, and bacteria, usually quite small
– gasses: CO2, Oxygen, various Nitrogen containing gasses, etc.
– water
The exact mixture various significantly from place to place.
It is a mix of things. A lot of it is minerals. A mixture of sand, silt, clay, pebbles, etc. Typically more then half of the soil is minerals. The rest is organic. Of course you can see the bugs and the twigs. But most of the organic matter is bacteria which are so tiny you can only see them as tiny specs on a microscope. Some of these bacteria even produce glue to keep the soil together. In addition to the bacteria there are lots of other microscopic microbes like amoeba and nematodes. These are single celled organisms which eat bacteria. And of course they poop out what they don’t eat so there are lots of free proteins, amino acids, fats, etc. in the soil as well. As for the larger structures there are almost always a few big fungal networks in the soil. These are made of thin strands that you might sometimes see when digging. They stretch on for large areas, typically through the entire biome. So a single mushroom might be the size of your neighborhood connecting all your gardens together. And it may go down into the bedrock for miles.
It has two main components.
Organic matter which is mostly fairly stable carbon compounds like cellulose and lignin.
Inorganic matter which is mostly oxides and carbonates of various things like silica, aluminium, calcium in the form of sand and pebbles.
It also generally contains some amount of air and/or water, as well as trace minerals dissolved into the water it contains.
And a decent portion of the mass of soil is biomass of microbes living in it.
Soil is primarily made up of:
-very decomposed organic matter that has either been repeatedly eaten, digested, and pooped out, first by herbivores or carnivores and then by detritovores like worms and springtails, and then finally fungi and bacteria, or dead plant or animal matter that was directly decomposed by fungi and microbes.
-Some less decomposed organic matter, like wood bits
-Sand and rocks, and sometimes clay and other minerals.
-Living organisms. bacteria, fungi, slime molds, amoebas, roots, algae, larger critters.
Plants don’t actually need soil, or rather not all plants need soil. There are a large number of plants on earth today that are known as Epiphytes(grow on other plants, like moss or bark) and Lithophytes(grow on rocks), These plants often look very different from your conventional plants due to unusual survival strategies, but they make it work. Over time as they grow, reproduce, and die, their corpses formed the base for soil. Many of these plants were designed to be very efficient in collecting, absorbing, and either conserving water or surviving a lack of water. They would pry minerals from the rocks or bark they grow on, collect trace nutrients that wash off rocks during rain or blow in as dust.
Some examples of these types of plants include many types of mosses, bromeliads, air plants, a wide variety of orchids such as moth orchids, sempervivums, butterworts, many species of ferns like staghorn ferns, and even some cactus species! Even some Fungi get in on the action, such as Lichens. The earliest land plants would have consisted of Mosses and Liverworts alongside Lichens primarily, growing on weathering rock or gravel that released minerals as it slowly dissolved in water, meanwhile without any plants to hold it back, dry areas of the continents would have kicked up nutrient-rich dust and blown it onto wetter areas for these early plants to absorb.
To your second question, before there were microbes on land, the plants from the water, which only needed sunlight and CO2, started to grow on land. then they died, decomposed and microbes started eating the dead plants.
Only the topsoil is organic, a few inches to a few feet below the surface the soil stops containing organic material and is just a mix of gravel/sand/silt/clay particles, water, and air
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.
Latest Answers