Notes

What do plants need to grow? The obvious answer might be water and sunlight, but many plants also need soil. Soil is the weathered material on the surface of the Earth, made up of sediment, water, air, and decayed organic matter. Soil is essential for most land plants because it contains the nutrients that they need to grow. Because plants need soil, soil is also important for the animals that eat plants. Even carnivores rely on soil because soil is necessary to feed the animals that carnivores eat.

Soil is made up of several different components. However, the largest component is sediment, which comes from bedrock. Bedrock is the layer of rock found just below the soil. Over time, bedrock weathers and mixes with the soil above it.


The different particles of rock that are found in soil can be categorized by size. Gravel is the term for a large rock particle that is found in some soils. In order of decreasing size, sand and silt come next. Clay is the term for the smallest particles of rock that make up soil. Different samples of soil have different combinations of particle sizes. Some may be made up of mostly gravel and sand, while others may contain mostly silt and clay. Loam is a type of soil that has roughly equal amounts of sand, silt, and clay.