Land or ground, also known as dry land, is the terrestrial surface of Earth that is not permanently submerged in water. It makes up 29% of Earth's surface and includes the continents and a variety of small islands. The zone where land meets sea or lakes is known as the coast. Land is an important part of Earth's climate system and plays important roles in the carbon cycle, nitrogen cycle, and water cycle. Though modern terrestrial plants and animals evolved from aquatic creatures, Earth's first cellular life likely originated on land. Several scientific disciplines study land, including geology and geography. One-third of land is covered in trees, 15% in crops, and a tenth in permanent snow and glaciers. Earth's land surface is almost entirely covered by regolith, a surface layer of rock, soil and minerals that forms the outer part of Earth's crust.: 222
The terrain varies greatly and consists of mountains, deserts, plains, plateaus, glaciers, and other landforms. In physical geology, land is divided into two major categories: relatively flat interiors called cratons, and mountain belts, which are formed over millions of years through plate tectonics.: 57 A major part of Earth's water cycle, streams shape the landscape, carve rocks, transport sediments, and replenish groundwater. At high elevations or latitudes, snow is compacted and recrystallized over hundreds or thousands of years to form glaciers, which can be so heavy that they warp the Earth's crust. About 30% of land has a dry climate, due to losing more water through evaporation than it gains from precipitation. Since warm air rises, this generates winds, though the Earth's rotation and uneven sun distribution also play a part.
The zone where land meets sea or lakes is known as the coast. Various natural boundaries can mark this separation, whether cliffs, solid rock landforms, marshes, or swamps. Since coastlines often change with the tide, the coast's baseline is the legal demarcation used to determine exclusive economic zones; often, the low-water line is used as the baseline.
Life on land depends on fresh water from rivers, streams, lakes, and glaciers, which constitute only 3% of the water on Earth. Prehistoric humans are thought to have settled near rivers; more recently, Neolithic civilizations were also concentrated near rivers for hydration and agriculture. The vast majority of human activity throughout history has occurred in land areas that support agriculture, habitat, and various natural resources. Today, 95% of the world's population lives on 10% of the land. Land use refers to the human allocation of land for various purposes, including farming, ranching, and recreation (e.g. national parks); one-third of land is used for agriculture. In recent decades, scientists and policymakers have emphasizes the need to manage land and its biosphere more sustainably, notably by restoring degraded soil, preserving biodiversity, protecting endangered species, and addressing climate change.
Land is commonly defined by its topography and geography. Modern scholars have adopted a more integrative view, and also use land to refer to its natural resources, physical coverage (rock, sand, soil, ice), biosphere (fauna and flora), climate, groundwater reserves, ecological processes like the rock, nitrogen, or water cycles. Land cover refers to the material physically present on the land surface, for example woody crops, herbaceous crops, barren land, shrub-covered areas. Artificial surfaces (including cities) account for about a third of one per cent 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. In economics, land refers to a factor of production. It can be leased in exchange for rent, and its various resources (trees, oil, metals) can be used as raw material.
The word land is derived from the Old English land 'ground, soil', also 'definite portion of the earth's surface, home region of a person or a people, territory marked by political boundaries'. It evolved from the Proto-Germanic *landą and from the Proto-Indo-European *lendʰ- 'land, open land, heath'. The word has many cognates in other languages, such as Old Norse: land, Old Frisian: land, Gothic: land, German: Land, Old Irish: land, Middle Welsh: llan 'an open space', Welsh: llan 'enclosure, church', Breton: lann 'heath', Church Slavonic: ledina 'wasteland, heath', and Czech: lada 'fallow land'. Etymological evidence within Gothic usage suggests that the original meaning of land was 'a definite portion of the earth's surface owned by an individual or home of a nation.' The meaning was extended to 'solid surface of the earth'. The original meaning is now associated with country.
A continuous area of land surrounded by an ocean is called a landmass. Although it may be most often written as one word to distinguish it from the usage "land mass"—the measure of land area—it is also used as two words. Landmasses include supercontinents, continents, and islands. There are four major continuous landmasses on Earth: Afro-Eurasia, the Americas, Antarctica, and Australia. Land capable of being ploughed and used to grow crops, is called arable land. A country or region may be referred to as the motherland, fatherland, or homeland of its people. Many countries and other places have names incorporating the suffix, -land (e.g. England, Iceland, Greenland, Finland, Swaziland, and New Zealand).
The Indo-Iranian suffix -stan, ultimately descended from Proto-Indo-Iranian *sthāna-, is analogous to the suffix -land, and is present in many country and location names, such as Uzbekistan, Pakistan, and Afghanistan. The suffix is also used more generally, as in Persian rigestân (ریگستان) "place of sand, desert", golestân (گلستان) "place of flowers, garden", gurestân (گورستان) "graveyard, cemetery", Hindustân (هندوستان) "land of the Indo people".
Main article: Continent
Land is separated by bodies of water. Apart from small islands, land is made up of four landmasses, from largest to smallest: Afro-Eurasia, America, Antarctica and Australia, which are then grouped into continents. Up to seven geographical regions are commonly regarded as continents. Ordered from largest in area to smallest, these seven regions are: Asia, Africa, North America, South America, Antarctica, Europe, and Australia. There are between five and seven continents, depending on how they are grouped. Some group North America and South America together as America; Europe and Asia can also be grouped as Eurasia, or combined with Africa into Afro-Eurasia. Others do not count Antarctica as a continent. Most of the island countries and territories of the Pacific Ocean are frequently grouped with Australia to form a geographical region called Oceania.
Main article: Border
Borders are geographical boundaries, imposed either by geographic features (oceans, mountain ranges, rivers) or by political entities (governments, states, or subnational entities). Political borders can be established through warfare, colonization, or mutual agreements between the political entities that reside in those areas; the creation of these agreements is called boundary delimitation.
Some borders—including most states' internal administrative borders, or inter-state borders within the Schengen Area—are open and completely unguarded. Most political borders are partially or fully controlled, and may be crossed legally only at designated border checkpoints; adjacent border zones may also be controlled. Buffer zones may be setup on borders between belligerent entities to lower the risk of escalation.
See also: History of Earth
The earliest material found in the Solar System is dated to 4.5672±0.0006 bya (billion years ago); therefore, the Earth itself must have been formed by accretion around this time. The formation and evolution of the Solar System bodies occurred in tandem with the Sun. In theory, a solar nebula partitions a volume out of a molecular cloud by gravitational collapse, which begins to spin and flatten into a circumstellar disc, out of which the planets then grow (in tandem with the star). A nebula contains gas, ice grains and dust (including primordial nuclides). In nebular theory, planetesimals commence forming as particulate matter accrues by cohesive clumping and then by gravity. The assembly of the primordial Earth proceeded for 10–20 myr. By 4.54±0.04 bya, the primordial Earth had formed.
Earth's atmosphere and oceans were formed by volcanic activity and outgassing that included water vapour. The origin of the world's oceans was condensation augmented by water and ice delivered by asteroids, proto-planets, and comets. In this model, atmospheric "greenhouse gases" kept the oceans from freezing while the newly forming Sun was only at 70% luminosity. By 3.5 bya, the Earth's magnetic field was established, which helped prevent the atmosphere from being stripped away by the solar wind. The atmosphere and oceans of the Earth continuously shape the land by eroding and transporting solids on the surface.
The crust, which currently forms the Earth's land, was created when the molten outer layer of the planet Earth cooled to form a solid mass as the accumulated water vapour began to act in the atmosphere. Once land became capable of supporting life, biodiversity evolved over hundreds of million years, expanding continually except when punctuated by mass extinctions.
The two models that explain land mass propose either a steady growth to the present-day forms or, more likely, a rapid growth early in Earth history followed by a long-term steady continental area. Continents formed by plate tectonics, a process ultimately driven by the continuous loss of heat from the Earth's interior. On time scales lasting hundreds of millions of years, the supercontinents have formed and broken apart three times. Roughly 750 mya (million years ago), one of the earliest known supercontinents, Rodinia, began to break apart. The continents later recombined to form Pannotia, 600–540 mya, then finally Pangaea, which also broke apart 180 mya.
Terrain or relief (also topographical relief) refers to the vertical and horizontal dimensions of the land's surface, while hypsometry studies terrain relative to sea level. In physical geography, terrain is the lay of the land. This is usually expressed in terms of the elevation, slope, and orientation of terrain features. Terrain affects surface water flow and distribution. Over a large area, it can affect weather and climate patterns. Relief (or local relief) refers specifically to the quantitative measurement of vertical elevation change in a landscape. It is the difference between the maximum and minimum elevations within a given area; most land has relatively low relief. The elevation of Earth's land surface varies from the low point of −418 m (−1,371 ft) at the Dead Sea, to a maximum altitude of 8,848 m (29,029 ft) at the top of Mount Everest. The mean height of land above sea level is about 797 m (2,615 ft), with 98.9% of dry land situated above sea level.
The terrain of a region largely determines its suitability for human settlement: flatter alluvial plains tend to have better farming soils than steeper, rockier uplands.
Main article: Biome
A biome is a biogeographical unit consisting of a biological community that has formed in response to the physical environment in which they are found and a shared regional climate. Biomes may span more than one continent. Biome is a broader term than habitat and can comprise a variety of habitats.
Main article: Desert
A desert is a barren area of landscape where little precipitation occurs and, consequently, living conditions are hostile for plant and animal life. The lack of vegetation exposes the unprotected surface of the ground to denudation. About one-third of the land surface of the Earth is arid or semi-arid. This includes much of the polar regions, where little precipitation occurs, and which are sometimes called polar deserts or "cold deserts". Deserts can be classified by the amount of precipitation that falls, by the temperature that prevails, by the causes of desertification, or by their geographical location.
Main article: Tundra
Tundra is a biome where tree growth is hindered by frigid temperatures and short growing seasons. The term tundra comes through Russian тундра (tundra) from the Kildin Sámi word тӯндар (tūndâr) meaning "uplands", "treeless mountain tract". There are three regions and associated types of tundra: Arctic tundra, alpine tundra, and Antarctic tundra.
Main article: Forest
A forest is an area of land dominated by trees. Hundreds of definitions of forest are used throughout the world, incorporating factors such as tree density, tree height, land use, legal standing, and ecological function. The United Nations' Food and Agriculture Organization (FAO) defines a forest as, "Land spanning more than 0.5 hectares with trees higher than 5 meters and a canopy cover of more than 10 per cent, or trees able to reach these thresholds in situ. It does not include land that is predominantly under agricultural or urban use." Using this definition, Global Forest Resources Assessment 2020 (FRA 2020) found that forests covered 4.06 billion hectares (10.0 billion acres; 40.6 million square kilometres; 15.7 million square miles), or approximately 31 per cent of the world's land area in 2020.
Main article: Grassland
Grasslands are areas where the vegetation is dominated by grasses (Poaceae). However, sedge (Cyperaceae) and rush (Juncaceae) can also be found along with variable proportions of legumes, like clover, and other herbs. Grasslands occur naturally on all continents except Antarctica and are found in most ecoregions of the Earth. Furthermore, grasslands are one of the largest biomes on earth and dominate the landscape worldwide. There are different types of grasslands: natural grasslands, semi-natural grasslands, and agricultural grasslands. They cover 31–69% of the Earth's land area.
Main article: Plateau
A plateau, also called a high plain or a tableland, is an area of a highland consisting of flat terrain that is raised sharply above the surrounding area on at least one side. Often one or more sides have deep hills or escarpments. Plateaus can be formed by a number of processes, including upwelling of volcanic magma, extrusion of lava, and erosion by water and glaciers. Plateaus are classified according to their surrounding environment as intermontane, piedmont, or continental. A few plateaus may have a small flat top while others have wide ones.
Erosion and tectonics, volcanic eruptions, flooding, weathering, glaciation, the growth of coral reefs, and meteorite impacts are among the processes that constantly reshape Earth's surface over geological time. The pedosphere is the outermost layer of Earth's continental surface and is composed of soil and subject to soil formation processes.
Land cover is the physical material at the surface of the earth. Among many things, it includes of grass, asphalt, trees, bare ground, water. Earth cover is the expression used by ecologist Frederick Edward Clements that has its closest modern equivalent being vegetation.: 52 The expression continues to be used by the United States Bureau of Land Management.
There are two primary methods for capturing information on land cover: field survey and analysis of remotely sensed imagery. Land change models can be built from these types of data to assess changes in land cover over time. One of the major land cover issues (as with all natural resource inventories) is that every survey defines similarly named categories in different ways. For instance, there are many definitions of "forest"—sometimes within the same organisation—that may or may not incorporate various forest features (e.g., stand height, canopy cover, strip width, the inclusion of grasses, and rates of growth for timber production). Areas without trees may be classified as forest cover "if the intention is to re-plant" (UK and Ireland), while areas with many trees may not be labelled as forest "if the trees are not growing fast enough" (Norway and Finland).
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.
Main article: Soil
Soil, also known as earth, dirt, or pedolith, 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 with associated 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 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 silicates (Al-Si) and has a lower density compared to the oceanic crust, called sima which is richer in magnesium silicate (Mg-Si) minerals. 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 third form of rock material found on Earth is metamorphic rock, which is created from the transformation of pre-existing rock types through high pressures, high temperatures, or both. 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.
The area where land meets the ocean or another large body of water like a lake is called a coast or, alternatively, a "coastline". The Earth has around 620,000 kilometres (390,000 mi) of coastline. When land is in contact with bodies of water, the land is likely weathered and eroded. The precise weathering of a coastline may be impacted by the tides, caused by changes in gravitational forces on larger bodies of water.
Coasts are important zones in natural ecosystems, often home to a wide range of biodiversity. On land, they harbour important ecosystems such as freshwater or estuarine wetlands, which are important for bird populations and other terrestrial animals. In wave-protected areas they harbor saltmarshes, mangroves or seagrasses, all of which can provide nursery habitat for finfish, shellfish, and other aquatic species. Rocky shores are usually found along exposed coasts and provide habitat for a wide range of sessile animals (e.g. mussels, starfish, barnacles) and various kinds of seaweeds. Along tropical coasts with clear, nutrient-poor water, coral reefs can often be found between depths of 1–50 meters (3.3–164.0 feet).
According to a United Nations atlas, 44% of all people live within 150 km (93 mi) of the sea. Because of their importance in society and high concentration of population, the coast is important for major parts of the global food and economic system, and they provide many ecosystem services to humankind. For example, important human activities happen in port cities. Coastal fisheries (commercial, recreational, and subsistence) and aquaculture are major economic activities and create jobs, livelihoods, and protein for the majority of coastal human populations. Other coastal spaces like beaches and seaside resorts generate large revenues through tourism. Marine coastal ecosystems can also provide protection against sea level rise and tsunamis. In many countries, mangroves are the primary source of wood for fuel (e.g. charcoal) and building material. Coastal ecosystems like mangroves and seagrasses have a much higher capacity for carbon sequestration than many terrestrial ecosystems, and as such can play a critical role in the near future to help mitigate climate change effects by uptake of atmospheric anthropogenic carbon dioxide.
The land of Earth interacts with and influences climate heavily since the land's surface heats up and cools down faster than air or water. Latitude, elevation, topography, reflectivity, and land use all have varying effects. The latitude of the land will influence how much solar radiation reaches the surface. High latitudes receive less solar radiation than low latitudes. The land's topography is important in creating and transforming airflow and precipitation on Earth. Large landforms, such as mountain ranges, divert wind energy and make air parcels less dense and therefore able to hold less heat. As air rises, this cooling effect causes condensation and precipitation.
The reflectivity of the earth is called planetary albedo, and the type of land cover that receives energy from the Sun affects the amount of energy that is reflected or transferred to Earth. Vegetation has a relatively low albedo meaning that vegetated surfaces are good absorbers of the sun's energy. Forests have an albedo of 10–15% while grasslands have an albedo of 15–20%. In comparison, sandy deserts have an albedo of 25–40%.
Land use by humans also plays a role in the regional and global climate. Densely populated cities are warmer and create urban heat islands that have effects on the precipitation, cloud cover, and temperature of the region.
Out of Africa, humans first evolved approximately 500,000 years ago, and from there travelled by land to settle Eurasia and the Americas by crossing the Bering land bridge by around 16,500 years ago. Human exploration of Earth saw its most dramatic rise during the Age of Discovery, when European explorers sailed and charted much of the rest of the world, leading to their discovery of the Americas and the Columbian exchange. Major explorations of Earth continued after the Age of Discovery.
Historically, exploration has been linked to invasions, conquest, and colonization.
Main article: Travel
Humans have commonly traveled for business, pleasure, discovery, and adventure, all made easier in recent human history as a result of technologies like cars, trains, planes, and ships. Land navigation is a subset of travel and refers to progressing through unfamiliar terrain using navigational tools like maps with references to terrain, a compass, or satellite navigation. Navigation on land is often facilitated by reference to landmarks – enduring and recognizable natural or artificial features that stand out from their nearby environment that are often visible from long distances. Natural landmarks can be characteristic features, such as mountains or plateaus. Examples of natural landmarks include Table Mountain in South Africa, Mount Ararat in Turkey, Uluru in Australia, and Mount Fuji in Japan.
Migration is the movement of people from one place to another with intentions of settling, permanently or temporarily, in a new country (external migration), or a new region of their country (internal migration). Migration is often associated with better human capital at both individual and household levels, and with better access to migration networks, facilitating a possible second move. Age is also important for both work and non-work migration. People may migrate as individuals, in family units or in large groups.
Tourism refers to short-term trips outside the person's usual environment undertaken for pleasure or business. Tourism can be domestic (within the traveller's own country) or international, and can generate important economic activity.
Trade has occurred since the prehistoric era. Peter Watson dates the history of long-distance commerce from c. 150,000 years ago. Many trade routes throughout history have existed predominantly on land such as the Silk Road which linked East Asia with Europe and the Amber Road which was used to transfer amber from Northern Europe to the Mediterranean Sea. The Dark Ages led trade to collapse in the West, but it continued to flourish among the kingdoms of Africa, the Middle East, India, China, and Southeast Asia. During the Middle Ages, Central Asia was the economic centre of the world, and luxury goods were commonly traded in Europe. Physical money (either barter or precious metals) was dangerous to carry over a long distance. To address this, a burgeoning banking industry enabled the shift to movable wealth or capital, making it far easier and safer to trade across long distances. After the Age of Sail, international trade mostly occurred along sea routes, notably to prevent intermediary countries from being able to control trade routes and the flow of goods.
Main article: Land use
Land use involves the management and modification of the natural environment or wilderness into built environment such as settlements and of semi-natural habitats such as arable fields, pastures, and managed woods. Land use by humans has a long history, first emerging more than 10,000 years ago. It has been defined as "the purposes and activities through which people interact with land and terrestrial ecosystems" and as "the total of arrangements, activities, and inputs that people undertake in a certain land type." Land use and land management practices have a major impact on natural resources including water, soil, nutrients, plants, and animals. Human tribes since prehistory have segregated land into territories to control the use of land. Today, the total arable land is 10.7% of the land surface, with 1.3% being permanent cropland. A third of Earth's land surface is used for agriculture, with estimated 16.7 million km2 (6.4 million sq mi) of cropland and 33.5 million km2 (12.9 million sq mi) of pastureland.
Main article: Earth in culture
Creation myths in many religions recall a story involving the creation of the world by a supernatural deity or deities, including accounts wherein the land is separated from the oceans and the air. The Earth itself has often been personified as a deity, in particular a goddess. In many cultures, the mother goddess is also portrayed as a fertility deity. To the Aztecs, Earth was called Tonantzin—"our mother"; to the Incas, Earth was called Pachamama—"mother earth". The Chinese Earth goddess Hou Tu is similar to Gaia, the Greek goddess personifying the Earth. Bhuma Devi is the goddess of Earth in Hinduism, influenced by Graha. In Norse mythology, the Earth giantess Jörð was the mother of Thor and the daughter of Annar. Ancient Egyptian mythology is different from that of other cultures because Earth (Geb) is male and the sky (Nut) is female.
In early Egyptian and Mesopotamian thought, the world was portrayed as a flat disk floating in the ocean. The Egyptian universe was pictured as a rectangular box with a north–south orientation and a slightly concave surface, with Egypt in the centre. A similar model is found in the Homeric account of the 8th century BC in which "Okeanos, the personified body of water surrounding the circular surface of the Earth, is the begetter of all life and possibly of all gods." The biblical earth is also a flat disc floating on water.
The Pyramid Texts and Coffin Texts reveal that the ancient Egyptians believed Nun (the ocean) was a circular body surrounding nbwt (a term meaning "dry lands" or "islands"), and therefore believed in a similar Ancient Near Eastern circular Earth cosmography surrounded by water.
The spherical form of the Earth was suggested by early Greek philosophers, a belief espoused by Pythagoras. Contrary to popular belief, most educated people in the Middle Ages did not believe the Earth was flat: this misconception is often called the "Myth of the Flat Earth". As evidenced by thinkers such as Thomas Aquinas, the European belief in a spherical Earth was widespread by this point in time. Prior to circumnavigation of the planet and the introduction of space flight, belief in a spherical Earth was based on observations of the secondary effects of the Earth's shape and parallels drawn with the shape of other planets.
Environmental science studies the Earth's environmental processes, and analyzes how humans can meet their needs while using land more efficiently and preserving its natural resources. Major current land-related environmental issues include climate change, pollution, environmental degradation, and resource depletion. The conservation movement lobbies for protection of endangered species and protection of any ecologically valuable natural areas. Sea level rise as a result of climate change is expected to result in currently-habited land becoming submerged, resulting in mass migration and ecosystem loss. International frameworks for environmental issues focus on three key issues as the "triple planetary crises": climate change, nature and biodiversity loss, and pollution and waste. The protection of life on land is one of the United Nations' Sustainable Development Goals.
Main article: Pollution
Air pollution can be caused by both human activities (like travel) and natural phenomena. There are many different types of air pollutants, such as gases (including ammonia, carbon monoxide, sulfur dioxide, nitrous oxides, methane, carbon dioxide and chlorofluorocarbons), particulates (both organic and inorganic), and biological molecules. The main stationary air pollution sources include coal power plants, oil refineries, and incinerators. Air pollution is a significant risk factor for many diseases, including respiratory infections, heart disease, COPD, stroke and lung cancer. Growing evidence suggests that air pollution exposure may be associated with reduced IQ scores, impaired cognition, increased risk for psychiatric disorders such as depression and detrimental perinatal health. Smog was a major issue in many countries during the 20th century; in London, the Great Smog of December 1952 killed nearly 12,000 people in 6 days. CFCs contributed to ozone depletion, and were phased out under the Montreal Protocol. America produces roughly 25% of the world's CO2. In 2007, China overtook the United States as the world's biggest producer of CO2, while still far behind based on per capita pollution (ranked 78th in the world).
Water pollution is the contamination of lakes, rivers, aquifers, reservoirs and groundwater as a result of human activities.: 6 It may be caused by toxic substances (e.g., oil, metals, plastics, pesticides, persistent organic pollutants, industrial waste products), stressful conditions (e.g., changes of pH, hypoxia or anoxia, increased temperatures, excessive turbidity, unpleasant taste or odor, and changes of salinity), or pathogenic organisms. For example, releasing inadequately treated wastewater into natural waters can lead to the degradation of aquatic ecosystems. Excessive emissions of sulphur dioxide and nitrogen oxide can cause acid rain, leading to soil degradation. Groundwater pollution occurs when pollutants are released to the ground and make their way into aquifers; these aquifers may spread the contaminants over a large area, and lead to the contamination of wells, seeps and springs, harming human and wildlife health.
Water pollution reduces the ability of the body of water to provide the ecosystem services (such as drinking water) that it would otherwise provide, and can lead to water-borne diseases for people using polluted water for drinking, bathing, washing or irrigation. Control of water pollution requires appropriate infrastructure and management plans as well as legislation. Technological solutions can include improving sanitation, sewage treatment, industrial wastewater treatment, agricultural wastewater treatment, erosion control, sediment control and control of urban runoff (including stormwater management).
Biodiversity loss refers to the worldwide extinction of various species, as well as the local reduction or loss of species in a certain habitat. Biodiversity loss can sometimes be reversed through ecological restoration or ecological resilience; however, it may also be permanent (e.g. through land loss). The planet's ecosystem is quite sensitive: occasionally, minor changes from a healthy equilibrium can have dramatic influence on a food web or food chain, up to and including the coextinction of that entire food chain. Biodiversity loss leads to reduced ecosystem services, and can eventually threaten food security. Earth is currently undergoing its sixth mass extinction (or Holocene extinction) as a result of human activities which push beyond the planetary boundaries. So far, this extinction has proven irreversible.
World leaders and supranational organizations are increasingly focused on addressing biodiversity loss. For example, the UN Convention on Biological Diversity is a treaty meant to biodiversity loss and proactively conserving wild areas. The fifteenth UN SDG goal ("Life on land") proposes 12 targets to be reached by 2030 and 14 indicators to measure progress, with annual updates delivered by the UN Secretary-General. In the 2022 update, the Secretary notes that deforestation targets have not been met, that the Red List Index has worsened by 10% over the past 3 decades, and that only a third of countries are on track to reach or exceed their national biodiversity targets.
Human-induced processes have led to biophysical degradation of wide swaths of land; these processes include human actions that can indirectly affect phenomena such as floods and bushfires.
Land degradation is considered an important topic of the 21st century due to its implications for agricultural productivity, the environment, and food security. It is estimated that up to 4% of the world's agricultural land is seriously degraded.
According to the Special Report on Climate Change and Land of the Intergovernmental Panel on Climate Change: "About a quarter of the Earth's ice-free land area is subject to human-induced degradation (medium confidence). Soil erosion from agricultural fields is estimated to be currently 10 to 20 times (no-tillage) to more than 100 times (conventional tillage) higher than the soil formation rate (medium confidence)".
The United Nations estimates that about 30% of land is degraded worldwide, and about 3.2 billion people reside in these degrading areas. About 12 million hectares of productive land – roughly equal to the size of Greece – is degraded every year. This happens because people exploit the land without protecting it. The United Nations Sustainable Development Goal 15 has a target to restore degraded land and soil and achieve a land degradation-neutral world by 2030 through sustainable agriculture.
Main article: Desertification
Desertification is a type of land degradation in drylands in which fertile areas become increasingly arid as a result of natural processes or human activities, resulting in loss of biological productivity. This spread of arid areas can be caused by a variety of factors, such as climate change and overexploitation of soil as a result of human activity. Throughout geological history, deserts have occurred naturally. In recent times, the potential influences of human activity, improper land management, deforestation and climate change on desertification is the subject of many scientific investigations.
And since Africa and Asia are connected at the Suez Peninsula, Europe, Africa, and Asia are sometimes combined as Afro-Eurasia or Eurafrasia. The International Olympic Committee's official flag, containing [...] the single continent of America (North and South America being connected as the Isthmus of Panama).
Our analysis of pedon data from several disturbed soil profiles suggests that physical disturbances and anthropogenic inputs of various materials (direct effects) can greatly alter the amount of C stored in these human "made" soils.
...at the first Earth Summit, the vast majority of the world's nations declared that human actions were dismantling the Earth's ecosystems, eliminating genes, species and biological traits at an alarming rate. This observation led to the question of how such loss of biological diversity will alter the functioning of ecosystems and their ability to provide society with the goods and services needed to prosper.
Moreover, we have unleashed a mass extinction event, the sixth in roughly 540 million years, wherein many current life forms could be annihilated or at least committed to extinction by the end of this century.
the process by which natural or human causes reduce the biological productivity of drylands (arid and semiarid lands). ... The concept does not refer to the physical expansion of existing deserts but rather to the various processes that threaten all dryland ecosystems.