Answer to Question 1
Answer: Soil is naturally occurring horizons of mostly loose mineral and organic constituents formed by weathering and biologic processes. The soil parent material is usually regolith rather than hard bedrock. Regolith is either fragments generated by physical weathering of underlying rock, or loose sediment transported from elsewhere. Soil is the part of the regolith that has horizons. Soil horizons differ from one another and from parent material by contrasting grain size, mineral composition, or both.
Answer to Question 2
Answer: Soil horizons are distinct because of differences in organic matter and mineral content that result from additions, subtractions, and transformations of minerals resulting from chemical weathering, and addition of organic matter. A and O horizons contain added organic matter. A horizons also show evidence of mineral subtraction. The E horizon, where present, is a nearly white horizon defined by an absence of organic matter, clay, colorful oxide and hydroxide minerals, or easily weathered minerals present in the parent material. The B horizon is notable for additions of colorful oxide and hydroxide minerals and clays. Calcite is present in arid-region B horizons. The C horizon is weakly weathered, unconsolidated regolith below the zone of accumulated minerals defining the B horizon.
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