Soil
Soil is a complex ecosystem supporting life and regulating Earth's cycles.
Soil, also commonly referred to as earth, is a mixture of organic matter, minerals, gases, water, and organisms that together support the life of plants and soil organisms. It is a complex three-state system of solids, liquids, and gases, and is a product of several factors including climate, relief, organisms, and parent materials interacting over time. Soil is regarded by ecologists as an ecosystem due to its complexity and strong internal connectedness.
- composition
- ~50% solids (45% mineral, 5% organic matter) and 50% voids (half water, half gas)
- dry_bulk_density
- 1.1 to 1.6 g/cm³
- particle_density
- 2.6 to 2.7 g/cm³
- prokaryotic_density
- ~10⁸ organisms per gram
- age_limit
- Little older than Pleistocene; none older than Cenozoic
- functions
- Medium for plant growth, water storage/purification, atmospheric modifier, habitat for soil organisms
Lore & Background
Soil consists of a solid matrix of minerals and organic matter, a porous phase holding gases (soil atmosphere), and a liquid phase (soil solution) containing dissolved substances. It develops through physical, chemical, and biological processes including weathering and erosion. Most soils have a dry bulk density between 1.1 and 1.6 g/cm³, while particle density ranges from 2.6 to 2.7 g/cm³. Little of Earth's soil is older than the Pleistocene, though fossilized soils date back to the Archean.
Reader's Guide
Soil is a major component of the Earth's ecosystem, providing critical ecosystem services such as nutrient recycling, water purification, and atmospheric modification. It acts as an important carbon reservoir, potentially reactive to human disturbance and climate change. Soil contains a prominent part of Earth's genetic diversity, with a gram of soil holding billions of organisms. Its functions include supporting plant growth, storing and purifying water, modifying the atmosphere, and serving as habitat. Soil science has two branches: edaphology (influence on living things) and pedology (formation and classification). In engineering, soil is part of the broader regolith concept.
Did You Know?
- A gram of soil can contain billions of organisms, belonging to thousands of species, mostly microbial and largely unexplored.
- Soil has a mean prokaryotic density of roughly 10⁸ organisms per gram, while the ocean has no more than 10⁷ per milliliter.
- Soils can effectively remove impurities, kill disease agents, and degrade contaminants, a property called natural attenuation.
- Mature soil profiles typically include three basic master horizons: A, B, and C.
More in Geology & Earth Surface 1-23
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