Introduction
A majority of soil is made up of air, and worms travelling through soil improve drainage and aeration, which promotes plant growth. Some people are connoisseurs of wine. Others are connoisseurs of chocolate. Earthworms are connoisseurs of soil. The earthworm--it spends its whole life eating and excreting dirt. If anyone understands the diversity and complexity of soil—it’s an earthworm. To your average earthworm, the difference between eating the soil at White River State Park and Fort Harrison State Park is like the difference between eating at Pizza Hut and White Castle.
While most people cannot tell the difference from one pile of dirt to another—plants, animals, and geologists can tell the difference. Subtle differences in soil affect what types of plants will grow, the density of plants, how water moves through the soil, and what animals and insects will live in the soil. Farmers are extremely interested in soil properties, as one soil type can lead to much stronger plant growth, which leads to more profit compared to another soil type.
When most people think of soil, they think of dirt, mud, and farming. Soil can be defined in two ways:
- Engineer/Construction Definition: Soil is any earth material that can be moved without blasting. Geologists use the term “sediment” to refer to any earth material that is not a rock.
- Geologist/Farmer: Soil is sediment/rock altered by weathering and capable of supporting rooted plant life
Most of you probably use the engineering definition of soil—meaning any loose earth material. In this section, we will be referring to the geologic definition of soil (which is commonly referred to as “top soil).” Geologists use soil to identify the layer of sediment exposed at Earth’s surface. This top most layer of sediment is altered into a soil by weathering and the accumulation of organic material. As a note, “dirt” does not have any scientific meaning—it is just a cultural term.
In addition to the information presented in the textbook, this lecture provides more information on the soils within Indiana, and problems that occur when soils become polluted.