Soil: Earth’s living skin — Earth science, 11–13 years
Soil is more than loose rock. It is a changing mixture of minerals, air, water, decayed matter and living organisms that supports plants and many food webs.
What soil is
Soil forms where crushed rock mixes with water, air and remains of living things. Tiny organisms break down dead leaves and animals, turning some of them into dark organic matter called humus. Different soils have different amounts of sand, clay, water and humus, so they do not all support the same plants.
Why soil matters
Plants need soil because it holds their roots, supplies water and provides dissolved minerals. People depend on it for crops, but soil can take centuries to form and can be lost quickly when bare ground is washed or blown away. Studying soil helps us decide how to grow food without using up this thin resource.
Reading a soil sample
A class puts soil and water in a jar, shakes it and leaves it still. After a few hours, the heaviest sand settles at the bottom, finer silt forms a layer above it, and clay stays higher; floating dark pieces are organic matter. The layers are not a perfect laboratory test, but they reveal why the sample drains and holds water differently.
The trap: soil is just dirt
It is reasonable to call soil “dirt” because both can look like brown dust. The mistake is treating soil as lifeless rubbish: healthy soil contains pores filled with air or water, minerals, roots, fungi, bacteria and decaying material. Removing any one part can change how well plants grow and how water moves through the ground.
Soil outside school
Gardeners add compost, cover bare ground and avoid packing soil hard, because roots and soil organisms need spaces for air and water. Farmers may plant different crops or leave plant cover between harvests to protect the soil. These choices do not make every soil perfect, but they can slow nutrient loss and runoff.
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