5.8 KiB
| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Land | 5/9 | https://en.wikipedia.org/wiki/Land | reference | science, encyclopedia | 2026-05-05T07:20:45.096604+00:00 | kb-cron |
Land cover refers to the material physically present on the land surface, for example, woody crops, herbaceous crops, barren land, and shrub-covered areas. Artificial surfaces (including cities) account for about a third of a percent of all land. Land use refers to human allocation of land for various purposes, including farming, ranching, and recreation (e.g. national parks); worldwide, there are an estimated 16.7 million km2 (6.4 million sq mi) of cropland, and 33.5 million km2 (12.9 million sq mi) of pastureland. Land cover change detection using remote sensing and geospatial data provides baseline information for assessing the climate change impacts on habitats and biodiversity, as well as natural resources, in the target areas. Land cover change detection and mapping is a key component of interdisciplinary land change science, which uses it to determine the consequences of land change on climate. Land change modeling is used to predict and analyze changes in land cover and use.
=== Soil ===
Soil is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Soil consists of a solid phase of minerals and organic matter (the soil matrix), as well as a porous phase that holds gases (the soil atmosphere) and water (the soil solution). Accordingly, soil is a three-state system of solids, liquids, and gases. Soil is a product of several factors: the influence of climate, relief (elevation, orientation, and slope of terrain), organisms, and the soil's parent materials (original minerals) interacting over time. It continually undergoes development by way of numerous physical, chemical and biological processes, which include weathering and erosion. Given its complexity and strong internal connectedness, soil ecologists regard soil as an ecosystem. Soil acts as an engineering medium, a habitat for soil organisms, a recycling system for nutrients and organic wastes, a regulator of water quality, a modifier of atmospheric composition, and a medium for plant growth, making it a critically important provider of ecosystem services. Since soil has a tremendous range of available niches and habitats, it contains a prominent part of the Earth's genetic diversity. A gram of soil can contain billions of organisms, belonging to thousands of species, mostly microbial and largely still unexplored. Soil is a major component of the Earth's ecosystem. The world's ecosystems are impacted in far-reaching ways by the processes carried out in the soil, with effects ranging from ozone depletion and global warming to rainforest destruction and water pollution. With respect to Earth's carbon cycle, soil acts as an important carbon reservoir, and it is potentially one of the most reactive to human disturbance and climate change. As the planet warms, it has been predicted that soils will add carbon dioxide to the atmosphere due to increased biological activity at higher temperatures, a positive feedback (amplification). This prediction has, however, been questioned on consideration of more recent knowledge on soil carbon turnover.
=== Continental crust ===
Continental crust is the layer of igneous, sedimentary, and metamorphic rocks that forms the geological continents and the areas of shallow seabed close to their shores, known as continental shelves. This layer is sometimes called sial because its bulk composition is richer in aluminium silicate and has a lower density compared to the oceanic crust, called sima which is richer in magnesium silicate. Changes in seismic wave velocities have shown that at a certain depth (the Conrad discontinuity), there is a reasonably sharp contrast between the more felsic upper continental crust and the lower continental crust, which is more mafic in character. The composition of land is not uniform across the Earth, varying between locations and between strata within the same location. The most prominent components of upper continental crust include silicon dioxide, aluminium oxide, and magnesium. The continental crust consists of lower density material such as the igneous rocks granite and andesite. Less common is basalt, a denser volcanic rock that is the primary constituent of the ocean floors. Sedimentary rock is formed from the accumulation of sediment that becomes buried and compacted together. Nearly 75% of the continental surfaces are covered by sedimentary rocks, although they form about 5% of the crust. The most abundant silicate minerals on Earth's surface include quartz, feldspars, amphibole, mica, pyroxene and olivine. Common carbonate minerals include calcite (found in limestone) and dolomite. The rock that makes up land is thicker than oceanic crust, and it is far more varied in terms of composition. About 31% of this continental crust is submerged in shallow water, forming continental shelves.
== Life science ==
Land provides many ecosystem services, such as mitigating climate change, regulating water supply through drainage basins and river systems, and supporting food production. Land resources are finite, which has led to regulations intended to safeguard these ecosystem services, and a set of practices called sustainable land management.
=== Land biomes ===
A biome is an area "characterized by its vegetation, soil, climate, and wildlife." There are five major types of biomes on land: grasslands, forests, deserts, tundras, and freshwater. Other types of biomes include shrublands, wetlands, and polar ice caps. An ecosystem refers to the interaction between organisms within a particular environment, and a habitat refers to the environment where a given species or population of organisms lives. Biomes may span more than one continent, and contain a variety of ecosystems and habitats.