Earth's dry surface
Land, also known as dry land, ground, or earth, is the solid terrestrial surface of Earth not submerged by the ocean or another body of water. It makes up 29.2% of Earth's surface and includes all continents and islands. Earth's land surface is almost entirely covered by regolith, a layer of rock, soil, and minerals that forms the outer part of the crust. Land plays an important role in Earth's climate system, being involved in the carbon cycle, nitrogen cycle, and water cycle. One-third of land is covered in trees, another third is used for agriculture, and one-tenth is covered in permanent snow and glaciers. The remainder consists of desert, savannah, and prairie.
Land terrain varies greatly, consisting of mountains, deserts, plains, plateaus, glaciers, and other landforms. In physical geology, the land is divided into two major categories: Mountain ranges and relatively flat interiors called cratons. Both form over millions of years through plate tectonics. Streams – a major part of Earth's water cycle – 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 percent 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 Earth's rotation and uneven sun distribution also play a part.
Land is commonly defined as the solid, dry surface of Earth. It can also refer to the collective natural resources that the land holds, including rivers, lakes, and the biosphere. Human manipulation of the land, including agriculture and architecture, can also be considered part of land. Land is formed from the continental crust, the layer of rock on which soil. groundwater, and human and animal activity sits.
Though modern terrestrial plants and animals evolved from aquatic creatures, Earth's first cellular life likely originated on land. Survival on land relies on fresh water from rivers, streams, lakes, and glaciers, which constitute only three percent of the water on Earth. The vast majority of human activity throughout history has occurred in habitable land areas supporting agriculture and various natural resources. In recent decades, scientists and policymakers have emphasized the need to manage land and its biosphere more sustainably, through measures such as restoring degraded soil, preserving biodiversity, protecting endangered species, and addressing climate change.
Definition.
Land is often defined as the solid, dry surface of Earth. The word "land" may also collectively refer the collective natural resources of Earth, including its land cover, rivers, shallow lakes, its biosphere, the lowest layer of the atmosphere (troposphere), groundwater reserves, and the physical results of human activity on land, such as architecture and agriculture. The boundary between land and sea is called the shoreline.625
Etymology.
The word "land" is derived from Old English, from the Proto-Germanic word , "untilled land", and then the Proto-Indo-European , especially in northern regions that were home to languages like Proto-Celtic and Proto-Slavic. Examples include Old Irish "land", "land, plot, church building" and Old Irish "ithlann", "threshing floor", and Old East Slavic "ljadina" "wasteland, weeds".
A country or nation may be referred to as the motherland, fatherland, or homeland of its people.43 Many countries and other places have names incorporating the suffix -land (e.g. England, Greenland, and New Zealand). The equivalent suffix "-stan" from Indo-Iranian, ultimately derived from the Proto-Indo-Iranian * "sthāna-", is also present in many country and location names, such as Pakistan, Afghanistan, and others throughout Central Asia. The suffix is also used more generally, as in Persian () "place of sand, desert", () "place of flowers, garden", () "graveyard, cemetery", and "Hindustân" () "land of the Indo people".
Physical science.
The study of land and its history in general is called geography. Mineralogy is the study of minerals, and petrology is the study of rocks. Soil science is the study of soils, encompassing the sub-disciplines of pedology, which focuses on soil formation, and edaphology, which focuses on the relationship between soil and life.
Formation.
The earliest material found in the Solar System is dated to (billion years ago); therefore, 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 the nebular hypothesis, planetesimals begin to form as particulate matter accumulates by cohesive clumping and then by gravity. The primordial Earth's assembly took 10–. By , 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, protoplanets, and comets. In this model, atmospheric "greenhouse gases" kept the oceans from freezing while the newly formed Sun was only at 70% luminosity. By , 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.
Earth's crust formed when the molten outer layer of 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 millions of 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 are 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 (million years ago), one of the earliest known supercontinents, Rodinia, began to break apart. The continents later recombined to form Pannotia, 600–, then finally Pangaea, which also broke apart .
Landmasses.
A continuous area of land surrounded by an ocean is called a landmass. Although it is most often written as one word to distinguish it from the usage "land mass"—the measure of land area—it may also be written as two words. There are four major continuous landmasses on Earth: Africa-Eurasia, America (landmass), Antarctica, and Australia (landmass), which are subdivided into continents. Up to seven geographical regions are commonly regarded as continents. Ordered from greatest to least land area, these continents are Asia, Africa, North America, South America, Antarctica, Europe, and Australia.
Terrain.
Terrain refers to an area of land and its features. Terrain affects travel, mapmaking, ecosystems, and surface water flow and distribution. Over a large area, it can influence climate and weather patterns. 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.
Elevation is defined as the vertical distance between an object and sea level, while altitude is defined as the vertical distance from an object to Earth's surface. 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.
Relief refers to the difference in elevation within a landscape; for example, flat terrain would have "low relief", while terrain with a large elevation difference between the highest and lowest points would be deemed "high relief". Most land has relatively low relief. The change in elevation between two points of the terrain is called a slope or gradient. A topographic map is a form of terrain cartography which depicts terrain in terms of its elevation, slope, and the orientation of its landforms. It has prominent contour lines, which connect points of similar elevation, while perpendicular slope lines point in the direction of the steepest slope. Hypsometric tints are colors placed between contour lines to indicate elevation relative to sea level.
A difference between uplands, or highlands, and lowlands is drawn in several earth science fields. In river ecology, "upland" rivers are fast-moving and colder than "lowland" rivers, encouraging different species of fish and other aquatic wildlife to live in these habitats. For example, nutrients are more present in slow-moving lowland rivers, encouraging different species of macrophytes to grow there. The term "upland" is also used in wetland ecology, where "upland" plants indicate an area that is not a wetland. In addition, the term moorland refers to upland shrubland biomes with acidic soils, while heathlands are lowland shrublands with acidic soils.
Geomorphology.
Geomorphology refers to the study of the natural processes that shape land's surface, creating landforms.3 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.
Erosion transports one part of land to another via natural processes, such as wind, water, ice, and gravity. In contrast, weathering wears away rock and other solid land without transporting the land somewhere else. Natural erosional processes usually take a long time to cause noticeable changes in the landscape—for example, the Grand Canyon was created over the past 70 million years by the Colorado River, which scientists estimate continues to erode the canyon at a rate of 0.3 meters (1 foot) every 200 years. However, humans have caused erosion to be 10–40 times faster than normal, causing half the topsoil of the surface of Earth's land to be lost within the past 150 years.
Plate tectonics refers to the theory that Earth's lithosphere is divided into "tectonic plates" that move over the mantle.66 This results in continental drift, with continents moving relative to each other. The scientist Alfred Wegener first hypothesized the theory of continental drift in 1912. More researchers developed his idea throughout the 20th century into the now widely accepted theory of plate tectonics.
Several key characteristics define the modern understanding of plate tectonics. The place where two tectonic plates meet is called a plate boundary, with different geological phenomena occurring across different kinds of boundaries. For example, at divergent plate boundaries, seafloor spreading is usually seen, in contrast with the subduction zones of convergent or transform plate boundaries.
Earthquakes and volcanic activity are common in all types of boundaries. Volcanic activity refers to any rupture in Earth's surface where magma escapes, therefore becoming lava. The Ring of Fire, containing two-thirds of the world's volcanos, and over 70% of Earth's seismological activity, comprises plate boundaries surrounding the Pacific Ocean.68
Climate.
Earth's land interacts with and influences its 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 on climate. The latitude of the land will influence how much solar radiation reaches its surface. High latitudes receive less solar radiation than low latitudes. The land's topography is important in creating and transforming airflow and precipitation. Large landforms, such as mountain ranges, can 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.
Different types of land cover will influence the land's albedo, a measure of the solar radiation that is reflected, rather than absorbed and 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 percent while grasslands have an albedo of 15–20 percent. In comparison, sandy deserts have an albedo of 25–40 percent.
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.
Features.
A landform is a natural or manmade land feature. Landforms together make up a given terrain, and their arrangement in the landscape is known as topography. Landforms include hills, mountains, canyons, and valleys, as well as shoreline features such as bays, capes, and peninsulas.
Coasts