Short answers, pulled from the story.
Soil is a mixture of organic matter, minerals, gases, water, and organisms that together support plant and soil life. A typical soil is about 50 percent solids, with 45 percent mineral and 5 percent organic matter, and 50 percent voids that hold water and gas. This makes it a complex three-state system of solids, liquids, and gases.
Soil forms when climate, organisms, topography, parent material, and time interact, a set of factors known by the acronym CLORPT. It begins with the weathering of bedrock into mineral parent material, after which plants and microbes add organic matter and colloids wash downward to create distinct layers called horizons. Development proceeds fastest from bare rock in a warm climate under heavy rainfall.
A single gram of soil can contain billions of organisms belonging to thousands of species, with a mean prokaryotic density of roughly 10 to the 8th organisms per gram. A recent study suggested soil is likely home to 59 percent of the species on Earth, give or take 15 percent. Potworms lead with 98.6 percent of their species living in soil, followed by fungi at 90 percent.
Tropical soils often lack fertility because hot, humid, wet climates cause fast leaching and decomposition, removing the clay and humus colloids that hold most of a soil's cation-exchange capacity. In high-rainfall areas, basic cations are forced off the colloids and washed out, leaving the soil able to support only organisms efficient at nutrient uptake in very acid conditions.
Soil functions as a medium for plant growth, a means of water storage, supply, and purification, a modifier of Earth's atmosphere, and a habitat for soil organisms. It produces 98.8 percent of the food consumed by humans, regulates floods by absorbing and releasing rainwater, and cleans water as it percolates through. It also acts as a carbon sink, since about 57 percent of its biotic content is carbon.
Soil pH practically ranges from 3.5 to 9.5, because values beyond those extremes are toxic to life forms. Most agricultural crops do best in mineral soils at pH 6.5 and organic soils at pH 5.5. High acidity brings toxic amounts of aluminium and manganese, while pH above 9 reduces plant growth.