The soil of the earth controls the existence of people and other animals. Without it we wouldn't have plants and therefore we wouldn't be alive. Soil is actually created from many different life forms. The soil is born from an interaction of life and non-life. The soil is made up such material as of the rock from volcanoes and the bits of rock worn away from granite boulders by the work of water passing over it. Living things work on rock to break it down. Lichens cover rocks and emit acids which break it down, mosses cover rocks and take hold in bits of soil.
Living things form the soil and living things live in the soil and keep it alive. The soil constantly changes. New matter is added all the time to existing soil and other matter is taken away by living creatures. The most important organisms of the soil are the smallest. The bacteria in soil is phenomenally abundant. Fungi are only a little bit less numerous than bacteria. Algae are the third most important organisms in the soil. These three elements produce decay. They take the bits and pieces of plants and animal residues and convert them down into their component minerals. There's one kind of bacteria that is nitrogen fixing. If not for this, plants would starve for a lack of nitrogen. Other kinds of organisms make carbon dioxide. Other kinds perform oxidation and reductions so that iron, manganese, and sulfur are transformed into food for plants.
The other organisms in the soil are the mites and the wingless insects. These are microscopic and size but do the important work of breaking down plants and other litter of the forest floor and turning them into soil. These creatures are highly specialized. One creature might be responsible for breaking down the needles of pine trees when they fall to the ground.
There are also larger forms of life which work in the soil. Some live under the soil and some live on top of it. As they move up and down in the soil, they aerate it and therefore improve its drainage and the penetration of water to plant roots. The earthworm is one of the most important of these larger earth creatures. Charles Darwin has a book about the action of worms in creating earth. The worms bring soil from the bottom of the soil up and from the top of the soil down, thus rotating the earth. Darwin found that the work of earthworms alone adds a layer of soil up to one and a half inches thick over the course of ten years.
It's useful to think of the soil as the home of a community of organisms all working interactively to make soil out of plant and animal residues and to keep it alive. What happens to these creatures when poisonous pesticides are dumped onto the earth is not even known, yet it continues in massive amounts. Some studies have been done. They show the harm that insecticides do to the earth. In some cases, the natural chemical processes that happen in the soil are interrupted. For example, one such process is nitrification, which makes the nitrogen that's in the air available to the plants in the ground. One herbicide, 2,4-D interrupts nitrification. Several insecticides interrupt nitrification, thus making it impossible for plants to grow.
Insecticides upset the delicate balance of organisms in the soil. They can increase one kind of organism while killing off another. These changes change the productivity of the soil. They could even create pests out of formerly harmless organisms by killing of these organisms' natural enemies.
Insecticides stay in the soil a long time. Insecticides have been recovered in soil tests as long as twelve years after they were introduced into the soil. Even if someone puts only moderate amounts of insecticides into the soil, the problem remains, because that person will probably repeat the treatment several times, year after year, until there's a frightening accumulation of that poison in the earth. This phenomenon has been documented with the chlorinated hydrocarbon DDT which has been found up to 113 times as high in concentration as what was put into the soil originally.
Arsenic is a useful case to study. Arsenic used to be sprayed on tobacco plants. Even though people have stopped doing this, the soil in which tobacco is grown is still contaminated with arsenic. The arsenic content of U.S. cigarettes increased more than 300 percent from 1932 to 1952. Later, scientists found increases as much as 600 percent.
The lesson from this case is that insecticides are placed in the soil and then absorbed by plants. Plants vary in how much poisons they take up. Carrots, for example, are notoriously high in absorption of insecticides. Manufacturers that want to produce insecticide-free food have a very difficult time getting it. One baby food producer tried to find fruits and vegetables free of insecticides. Even though the current grower might not be using the chemical, the soil contained the chemicals from past sprayings. Sometimes insecticides actually kill the crops. Some plants are particularly sensitive to them, plants such as beans, what, barley and rye. Insecticides retard their root growth and keep seedlings from growing properly. Pesticides have been put on plants and then, after damage has been shown, withdrawn from the market, but not before the soil was permanently contaminated. Pesticides are building up in the soil year by year.
Carson continues her systematic treatment of all the elements of the world that are affected by insecticide poisoning. From water in chapter 4, she moves to the soil in chapter 5. This might be one of her most eloquent chapters in her appeal for people to realize the severe and lasting damage caused by pesticides. She begins the chapter with an exquisitely detailed account of what makes up the soil, especially of what makes the soil alive. She describes the soil's organisms in such detail in order to convince the reader of the importance of their work in actually creating soil and of the delicacy of their balance. Then, Carson begins to describe the wholesale dumping of pesticides into the world of microscopic creatures by people who don't even know the effects of what they're doing or even the world that they are disrupting.