<p> WEATHERING AND SOIL FORMATION Chapter 2 Section 2</p><p>SOIL  loose, weathered material on Earth’s surface in which plants can grow  a mixture of rock particles, minerals, decayed organic material, water, and air</p><p>HUMUS  dark-colored substance that forms as plants and animal remains decay  soil rich in humus has a high fertility</p><p>SOIL FORMATION  begins with the weathering of bedrock  continues over long period of time</p><p>HORIZON A  made of topsoil  develops as plants add organic material to soil  plant roots weather pieces of rock</p><p>HORIZON B  called subsoil  develops as rainwater washes clay and minerals from the A horizon  little humus</p><p>HORIZON C  contains only partly weathered rock  forms as bedrock weathers and rock breaks up into soil particles</p><p>DECOMPOSERS  organisms that break the remains of dead organisms into smaller pieces and digest them with chemicals</p><p>LIVING ORGANISM IN THE SOIL  earthworms do most of the work mixing the soil  add nitrogen to the soil when they produce waste  add organic material/humus when they die and decay  aerate or mix air into the soil</p>