Soil forms slowly from basement rock when the rock minerals undergo changes as they weather to soil, which includes minerals as inorganic parts.
When volcanoes cover an area with new rock in the form of lava, or when glaciers scrape it clean, new fresh soil, rich in mineral nutrients, can form.
Igneous rocks are eroded and weathered to form sediments and soil, but over time, the more valuable minerals are leached away, leaving a deficient soil.
Soil contains humus, a complex mixture of partly-decayed organic matter that supports a broad range of Fungi, bacteria and microscopic life forms.
The soil is commonly regarded as dead, but it includes organic parts as well as the more obvious minerals, and is of little use to plants if it is sterile.
Leaf litter is a key part of the soil and forest floor, and supports its own rich culture of living things, before it enters the soil as humus.
Many things live in the soil, and the animals in soil can be extracted and studied. The richer the soil, the more animals there will be living in it.
The quality of soil can be assessed by taking a soil profile, which means either digging a trench, or using an auger to bore out a sample to study the layers.
Hydroponics is a popular method of growing plants without soil, using water to supply the essential mineral nutrients that are needed by the plants.