Continent

Continents are conventionally conceived as extensive, coherent landmasses that, in the idealized model, are discrete from one another by expanses of water—so much so that each continent can be regarded as a kind of very large “island” when judged by separation. However, schemes that recognize five or more continents acknowledge that some continental units are connected by land, so practical boundaries may include contiguous terrestrial links rather than pure oceanic isolation. The distinction between a continent and an island rests in part on notions of size, but any numerical cutoff is arbitrary: for example, Greenland (approximately 2.17 × 10^6 km²) is classified as the largest island, whereas Australia (≈7.62 × 10^6 km²) is treated as the smallest continent, showing how different thresholds yield different classifications. All major landmasses are rimmed by the same continuous World Ocean, even though that ocean is conventionally partitioned into several principal basins according to continental arrangement and other geographic considerations. From a geological perspective, a continental unit is characterized by (1) elevation elevated relative to the adjacent oceanic floor; (2) a broad diversity of rock types—igneous, metamorphic and sedimentary—often enriched in silica; (3) crustal thickness substantially greater than surrounding oceanic crust; and (4) well-defined margins enclosing an area large enough to constitute a continental block.

Extent

The spatial extent of a continent depends on the definitional lens employed. In its most restrictive, traditional sense a continent is a single continuous expanse of dry land bounded by the coastline and any land borders; by this convention “continental Europe” excludes offshore islands such as Great Britain, Iceland, Ireland and Malta, and the “continent of Australia” can be taken to mean the Australian mainland apart from New Guinea, Tasmania and nearby isles. A familiar administrative application is the phrase “continental United States,” which commonly denotes the 49 states on the North American landmass (including Alaska but excluding Hawaii) plus the District of Columbia.

From a geological or physical‑geography perspective the boundary of a continent is extended seaward to the outer limit of the continental shelf, and islands resting on that shelf are treated as part of the same continental margin. Because shorelines change with sea level, this shelf‑based criterion often incorporates islands into adjacent continents (for example Great Britain and Ireland with Europe) and can join landmasses treated separately under stricter shoreline definitions (for example Australia with New Guinea). Taken to an extreme of shelf connectivity, continental classification can be reduced to a few large units—commonly Antarctica; Australia–New Guinea; and a vast Afro‑Eurasia–Americas assembly linked across the Bering margin—so large that some commentators have argued it could be regarded as a single dominant landmass.

In practice, cartographers and regional geographers frequently group island states and territories with a neighboring continental landmass on grounds of proximity and shelf relationships, and cultural, political and biogeographic associations likewise lead to inclusive classifications: Iceland is conventionally counted as European and Madagascar as African despite their insularity. Conversely, broader cultural‑geographic constructs such as “Oceania” merge the Australian continental core with numerous Pacific islands for regional purposes rather than as a strict geological unit. Consequently, the partitioning of Earth’s emergent land into continents, regions or quasi‑continents varies according to whether geological structure, geographic continuity, cultural affiliation or political convenience is prioritized.

Continental delineation is fundamentally a matter of convention rather than strict geomorphology. The dominant seven-continent schema treats continents as broadly discrete landmasses, but it routinely relaxes a literal requirement for complete oceanic isolation in favor of historical, cultural and practical considerations. Only Antarctica and Australia are entirely encircled by ocean under this framework; the remaining continents are connected to neighbors by relatively narrow terrestrial links or by contiguous continental shelves.

Two salient narrow connections illustrate this continuity. Africa and Asia meet at the Isthmus of Suez, and North and South America are joined by the Isthmus of Panama; in both cases the land bridges are minute when compared with the extents of the adjoining continents. Human-made cuts across these links—the Suez and Panama canals—are artificial, limited in scale and not generally treated as dividing features for continental status. Similarly, whether North and South America are regarded as separate continents depends on convention: the seven-continent model separates them, whereas many six-continent schemes (and historical practice in some regions) consider the Americas a single landmass, a viewpoint that persists in parts of Europe, Asia and across Latin America.

The Eurasian landmass presents another classificatory ambiguity. Physically continuous, it can be viewed either as a single continent (Eurasia) or as two (Europe and Asia); the former yields a six-continent world, the latter preserves the seven-continent ordering. Europe is physiographically a large peninsula of Eurasia but is conventionally treated as a separate continent—an assignment rooted more in historical and cultural tradition than in clear physical discontinuity. Critics argue that this Europe–Asia split reflects Eurocentric conventions, noting that regions such as China and India match Europe in geographic and cultural complexity; nonetheless, longstanding historical identities sustain Europe’s separate status in most modern classifications. By contrast, sizeable peninsulas such as the Indian subcontinent are typically classified as subcontinents rather than independent continents.

If one applies a strict criterion of wholly discrete landmasses, alternative consolidated schemes emerge. Merging Africa, Europe and Asia into an Afro‑Eurasian supercontinent and uniting North and South America into a single America produces a four‑continent model: Afro‑Eurasia, America, Antarctica and Australia. Paleogeographic evidence from the Pleistocene underscores the fluidity of continental boundaries: lower sea levels exposed extensive continental shelves and created land bridges (for example, Sahul linking Australia with New Guinea, the Bering land bridge between Eurasia and the Americas, Tasmania’s connection to mainland Australia, and temporary attachments of Great Britain to continental Europe). During glacial maxima the world’s dry land was effectively partitioned into a smaller number of large, continuous massifs—most notably an Africa–Eurasia–America complex, Antarctica, and Australia–New Guinea (Sahul)—highlighting that continental separation is both temporally variable and scale‑dependent.

Number of continents

Global schemes for defining continents are not uniform: authoritative classifications recognize four, five, six or seven continents depending on whether emphasis falls on uninterrupted landmass, physiographic regions, tectonic structures, or administrative convenience. Cartographic aids frequently depict these alternatives with similar colors for areas that may be merged or split, underscoring that continental boundaries are conceptual and discipline-dependent rather than uniquely determined.

The four‑continent model groups the world into Afro‑Eurasia (the continuous landmass often called the Old World), America (the New World), Antarctica, and Australia; it privileges land continuity and treats Africa, Europe and Asia as one contiguous unit. The five‑continent arrangement instead distinguishes Africa, Eurasia, America, Antarctica and Australia, reflecting a preference for broad physiographic and regional separation rather than strict continuity. Geological and tectonic perspectives commonly yield a six‑continent scheme—Africa, Eurasia, North America, South America, Antarctica and Australia—by separating the two American landmasses while retaining Eurasia as a single unit. Another six‑unit variant, used in some statistical and administrative contexts such as the United Nations Statistical Division, lists Africa, Asia, Europe, America, Antarctica and Australia, treating “America” as a single continental region for classification purposes.

The seven‑continent model—Africa, Asia, Europe, North America, South America, Antarctica and Australia—is the form most widely taught in many English‑speaking countries (including Australia, Canada, the UK and the US) and in several populous Asian and other states; it divides Eurasia into Europe and Asia and the Americas into North and South America. Regional traditions produce further variants: for example, the combined‑Eurasia plus separate North and South Americas version is prevalent in Russia and parts of Eastern Europe, whereas the combined‑America plus separate Eurasia approach is common in Greece and many Romance‑language countries, including much of Latin America.

Continents also carry cultural and symbolic meanings: the Olympic flag’s five interlaced rings represent the five inhabited continental regions under a combined‑America conception (excluding Antarctica because it has no permanent population). In English‑language geographical practice, the term “Oceania” is frequently used to denote the Pacific island states and territories together with the continent of Australia, providing a regional category that separates Pacific islands as a coherent unit from continental Australia in regional studies.

Zealandia: the submerged continental fragment

Zealandia is a predominantly submarine continental fragment beneath the southwestern Pacific Ocean that supports the islands of New Zealand and New Caledonia and extends east of Australia. Covering roughly 4.9 million km², the feature is largely inundated—about 94% lies below sea level—so that only limited portions of its crust remain emergent as island groups. The highest landform associated with this drowned plate is Aoraki / Mount Cook in New Zealand (3,724 m).

From a crustal perspective, Zealandia exhibits the characteristics typical of continental lithosphere: a relatively thick, buoyant sequence dominated by silicic and metamorphic rocks rather than the thin basaltic sequences of oceanic crust, a coherent spatial extent with identifiable margins, and broad bathymetric elevation relative to abyssal plains. These attributes form the basis for proposals to recognize Zealandia as a continent. Geologically, the fragment formed during the breakup of Gondwana in the Mesozoic; rifting that began well before the end of the Cretaceous separated it from Australia and Antarctica, leaving the unit largely submerged by roughly 80 million years ago.

The plate comprises several elevated submarine plateaus and rises—notably the Campbell Plateau, Chatham Rise, Lord Howe Rise and Challenger Plateau—that record its internal architecture and approximate boundaries. Its current shape and deformation reflect position within a complex plate‑boundary domain of the southwest Pacific: interactions among the Pacific Plate, Australian Plate and various microplates concentrate seismicity, volcanism and differential uplift/subsidence on and around the emergent margins (for example along New Zealand’s Alpine Fault and associated arc systems).

Long-term partial inundation and isolation have had pronounced biogeographic consequences. The remaining emergent areas preserve biotas with high levels of endemism and relictual lineages that document extended evolutionary isolation and changing sea levels and climates tied to Zealandia’s tectonic history. Although many earth scientists now treat Zealandia as a coherent continental fragment deserving the label “continent,” formal acceptance varies by discipline and depends on the criteria and definitions applied, so its status remains debated in some geographic and political contexts.

Area and population are presented here using a seven-continent model (Oceania defined to include Australasia together with Melanesia, Micronesia, and Polynesia). The combined terrestrial area equals 149,733,926 km2 (57,812,592 mi2), and the estimated world population for 2021 is 7,909,295,151.

Asia is the largest continent by both land and population, covering 44,614,000 km2 (17,226,000 mi2), or about 29.8% of Earth’s land surface, and accounting for approximately 4,694,576,167 people (59.4% of the global population). Africa encompasses 30,365,000 km2 (11,724,000 mi2), roughly 20.3% of terrestrial area, with an estimated 1,393,676,444 inhabitants (17.6% of the world total). North America occupies 24,230,000 km2 (9,360,000 mi2), or 16.2% of land area, and had about 595,783,465 residents in 2021 (7.5% of the global population). South America covers 17,814,000 km2 (6,878,000 mi2), representing 11.9% of land area, with a 2021 population of 434,254,119 (5.5% of the world). Antarctica’s landmass is 14,200,000 km2 (5,500,000 mi2), about 9.5% of Earth’s land surface; no permanent population was recorded in the 2021 estimate. Europe comprises 10,000,000 km2 (3,900,000 mi2), or 6.7% of terrestrial area, and had an estimated 745,173,774 people (9.4% of the world). Oceania, as defined here to include Australasia plus the Pacific subregions, totals 8,510,926 km2 (3,286,087 mi2), about 5.7% of land area, with an estimated population of 44,491,724 (0.6% of the global population).

The population figures follow United Nations geoscheme conventions for continental assignment: Egypt (including the Isthmus of Suez and the Sinai Peninsula) is counted in Africa; Armenia, Azerbaijan, Cyprus, Georgia, Indonesia (including Western New Guinea), Kazakhstan, and Turkey (including East Thrace) are counted in Asia; all of Russia (including Siberia) is assigned to Europe; Panama and the United States (including Hawaii) are assigned to North America; and Chile (including Easter Island) is assigned to South America.

A note on Australasia: for the purposes of these aggregates Australasia is treated as part of Oceania. Its constituent-area figures encompass Australia, New Zealand, and Papua New Guinea but exclude the Aru Islands and Western New Guinea; Australasia is not commonly regarded as a separate continent in much English-language usage.

Supercontinents

Supercontinents are episodic, large-scale assemblies of continental crust in which most of the Earth’s cratonic cores become joined into a single, contiguous landmass. Cratons—the stable, ancient portions of the continental lithosphere that retain deep crustal and mantle architecture—act as the fundamental building blocks of these assemblies. In geological usage the concept of “continent” therefore encompasses not only modern landmasses but also former continental configurations and long-lived supercontinents preserved in the rock record.

Multiple cycles of assembly and dispersal are recorded through Earth history. Named examples reconstructed from geological data include Vaalbara, Kenorland, Columbia, Rodinia, Pannotia and Pangaea; the reconstruction of Pangaea about 200 million years ago, for instance, captures continental positions immediately before the Mesozoic rifting that opened the Atlantic. Evidence for these past supercontinents derives from convergent lines of inquiry—correspondences in cratonic stratigraphy and lithology, paleomagnetic signatures that constrain ancient latitudes and orientations, and matching orogenic belts that mark former collisional margins—together demonstrating recurrent, planet-scale plate reorganizations.

After assembly, supercontinents fragment through processes such as continental rifting, initiation of seafloor spreading and continued plate motion. The progressive breakup of these former landmasses generated the major continental fragments that subsequently drifted, rotated and reassembled in different configurations to produce the continents observed today.

Subcontinents

A subcontinent denotes a clearly identifiable portion of a continent that is distinguished from the adjoining continental mass by prominent physical boundaries and treated as a discrete regional unit. In practice this separation is usually manifested as a large peninsula or peripheral landmass bounded by mountains, seas, isthmuses or similar natural barriers, so that the area has recognisable geographical unity while remaining part of the larger continental system.

Two principal rationales underlie the designation. The first is morphological: surface features and peripheral position—a large, peninsular form that is set apart from the continental interior—justify treating the area as a subcontinent. The second is geological: lithospheric distinction, where the region lies on a tectonic plate different from the adjacent continental plate, offers a deeper, crustal basis for separation. These criteria sometimes coincide but can also point to different conclusions.

The Indian subcontinent exemplifies the concept in its conventional, morphologically driven usage: a vast peninsular landmass bounded and made distinct by major mountain ranges and surrounding seas, and commonly invoked as the standard reference for what constitutes a subcontinent. By contrast, other large peripheral regions are variably described as subcontinental because of their prominent peripheral morphology or plate differences—candidate examples include the Arabian Peninsula, Southern Africa, the Southern Cone of South America and Alaska—each cited for pronounced separation from the continental interior.

Some cases challenge the peninsular model. Greenland, typically classed as the world’s largest island and located on the North American Plate’s periphery, is occasionally characterised as a subcontinent on tectonic or peripheral grounds rather than by the usual morphological criteria. Such usages underline that “subcontinent” is not an exclusively surface-geographic category.

The label also depends on the higher-level scheme adopted for continental division. If the Americas are treated as a single continent, they are commonly partitioned into subcontinents—typically North and South America, or alternatively North, Central and South America. Likewise, treating Eurasia as one unit yields Asia and Europe as subcontinental subdivisions. Thus the term’s application reflects both physical geography and conceptual framing.

In summary, “subcontinent” is a flexible category applied according to competing rationales—morphological separation versus tectonic distinctiveness—and its use varies with the spatial schema adopted. Interpreting any particular instance therefore requires attention to whether emphasis is placed on surface form, geological structure, or the classificatory convention in force.

Submerged continental crust comprises regions of continental-type lithosphere that lie predominantly below sea level rather than forming extensive emergent land. These domains are distinguished from typical oceanic seafloor by the presence of continental rock assemblages, relatively greater crustal thickness and complex internal structure, and a tectonic history tied to rifting, breakup and subsequent subsidence. Prominent examples are Zealandia—largely submerged but with emergent portions such as New Zealand and New Caledonia—and the Kerguelen Plateau, an extensive, mostly submerged plateau in the southern Indian Ocean whose size and crustal composition set it apart from normal oceanic basins. Such cases demonstrate that continental massifs and fragments may persist in submarine form, with islands and archipelagos providing the only surface expression of deeper continental crust. Identification and categorization of these features depend on multiple lines of geological evidence (rock types, crustal thickness and structure, relative elevation and tectonic history), so they are variously described as submerged continents, continental fragments or large plateaus according to the preponderance of attributes and ongoing interpretation. Because these submerged landmasses occur across different ocean basins, they exert important influences on regional geology, oceanography and biogeography through their bathymetric relief, isolated emergent areas and roles in former continental configurations.

Microcontinents are discrete islands underlain by continental lithosphere that have been severed from a larger continental mass through plate-tectonic processes. Unlike volcanic islands underlain by basaltic oceanic crust, these landmasses preserve the felsic composition and internal structures characteristic of continental crust. Their origin typically involves continental rifting—extension and breakup of a continental plate—followed by seafloor spreading that widens the intervening ocean basin and subsequent plate motions that transport the detached block away from its source continent.

The term “microcontinent” denotes this geological character while acknowledging limits of scale and autonomy: such fragments retain continental composition and structure but are too small and lack an independent tectonic identity to be classed as full continents. Their recognition depends on lithospheric properties rather than present-day political or geographic classification.

Madagascar provides the clearest exemplar: its bedrock and tectonic history demonstrate origin as a continental fragment rifted from the African margin, yet it is commonly treated as an island in geopolitical and regional contexts. The island’s long isolation exemplifies the wider biogeographic consequences of microcontinental separation: protracted separation fosters high levels of endemism and the evolution of distinctive lineages, a biological distinctiveness that has prompted some scientists to refer to Madagascar informally as an “eighth continent” in biogeographic terms.

Geological continents

In geological practice a continent is not defined solely by surface geography but by a combination of four measurable attributes that together distinguish continental blocks from the surrounding oceanic domain: relative elevation, characteristic rock assemblages, crustal structure, and clearly defined spatial limits with a minimum areal extent. These criteria are applied to identify coherent crustal regions—whether emergent or submerged—that differ fundamentally from oceanic lithosphere and seafloor bathymetry.

Elevation refers to a continent’s higher-standing crustal domain: continental regions form domal or thickened crust that sits higher in isostatic and crust–mantle equilibrium than adjacent oceanic lithosphere, even when portions are submerged. The geological makeup of a continental landmass must show the diversity typical of long-lived continental crust—igneous, metamorphic and sedimentary rocks that record crustal growth, recycling and the development of sedimentary basins. Correspondingly, continental crust exhibits a distinct crustal structure: it is generally thicker and characterized by lower seismic velocities than oceanic crust, reflecting compositional, thermal and density contrasts.

Spatial limits and size are integral to the classification: continental blocks must have definable boundaries and occupy an area exceeding one million square kilometres, so margin delineation and areal extent are essential criteria. By these measures Earth currently has seven recognized geological continents (Africa; Antarctica; Australia; Eurasia; North America; South America; Zealandia), the most recent addition being Zealandia (2017). Zealandia’s status was debated because of an apparent paucity of exposed Precambrian cratonic rocks, but subsequent work (notably a 2021 study) identified Precambrian portions of the submerged mass and older ages than previously recognized, strengthening the case that Zealandia meets continental criteria.

Finally, the seven geological continents are spatially isolated from one another by intervening oceanic lithosphere and related tectonic structures—ocean basins, mid‑ocean ridges, subduction zones and trenches, rift systems and transform faults—which provide the physical boundaries that separate continental blocks.

Early classical geographers articulated the idea of large terrestrial divisions both visually and linguistically: surviving imagery—such as Strabo depicted with a globe marked Europa and Asia—attests to attempts to map broad regional partitions, while the English word “continent” derives from the Greek ἤπειρος (originally the place-name Epirus), a term that later came to be applied to Asia (Asia Minor) and more generally to continuous landmasses.

The first systematic distinction between Europe and Asia emerged in maritime practice. Greek sailors named the lands on either side of a continuous seaway defined by the Aegean, the Dardanelles, the Sea of Marmara, the Bosporus and the Black Sea; these names initially designated coastal zones and were extended inland only as far as navigable rivers permitted. Inland from those waterways classical geographers often acknowledged the absence of any decisive physical feature that could divide a single Eurasian continent, and thus continental limits remained a matter of convention as much as of observation.

A parallel problem concerned the status of Africa (Libya). Classical debate ranged between treating Africa as part of Asia or recognising a tripartite world of Europe, Asia and Africa. By convention the threefold scheme predominated, with the Aegean region conceived as a central point and Europe located to the north and west, Asia to the east, and Africa to the south; nonetheless the precise lines between these divisions were disputed and multiple boundary models coexisted.

Among variant demarcations were a Europe–Asia line running from the Black Sea along the Rioni (Phasis) in modern Georgia, and an alternative route via the Kerch Strait into the Sea of Azov and thence inland along the Don (Tanais). The Nile was commonly taken as the Asia–Africa frontier, though Herodotus objected to splitting Egypt and placed the boundary at Egypt’s western limit; Eratosthenes records that some authorities used major rivers (notably the Nile and the Don) to isolate large tracts as if they were islands, while others preferred isthmuses—placing the Europe–Asia divide at the land-bridge between the Black Sea and the Caspian and the Asia–Africa line at the isthmus between the Red Sea and the Mediterranean near Lake Bardawil.

Roman and later authors reiterated and reshaped these conventions. Pliny declared the globe divisible into three parts and noted alternative schemes that effectively bisected the inhabited world (for example, a line from the Tanais to the Straits of Gades). In medieval cartography and theology the tripartite order became schematic and polemical: T and O maps depicted the three continents as the domains of Noah’s sons (Shem/Asia, Japheth/Europe, Ham/Africa), with the T formed by the waterways that medieval tradition treated as separators; ecclesiastical and Latin cultural identity also reinforced the notion of Europe as a distinct domain. Disputes over the correct boundaries—Suez versus the Nile or the Great Catabathmus for the Africa–Asia limit, and competing inland markers for Europe–Asia—survived into the modern period, with eighteenth‑century practice still reflecting earlier choices and the fundamental problem of partitioning an essentially continuous Eurasian landmass remaining unresolved for more than two millennia.

European engagement with the Americas unfolded rapidly after Christopher Columbus’s 1492 transatlantic crossing to the Caribbean, which inaugurated continuous voyages of exploration despite Columbus’s persistent insistence that he had reached Asia. A decisive reinterpretation of the newly encountered lands came with Amerigo Vespucci’s 1501 expedition, undertaken with Gonçalo Coelho, during which they passed Fernando de Noronha, made landfall on the Brazilian coast, and proceeded southward along an eastern South American shoreline that extended well beyond the known limits of Asia; these observations demonstrated that the landmass possessed continental dimensions. Vespucci’s account, published in Europe as Mundus Novus in 1502–1503 (a text apparently subject to editorial additions), explicitly characterized this southern land as a populous and fecund continent comparable to Europe, Asia, and Africa, providing the first clear European assertion of the Americas as a distinct continental entity.

Cartography responded quickly: by the mid-1500s the designation “New World” began to appear on contemporary charts—most notably on the Oliveriana (Pesaro) map of c.1504–1505—where South America was already treated as a separate landmass even while many maps continued to depict North America as attached to Asia. The major conceptual leap occurred with Martin Waldseemüller’s 1507 Universalis Cosmographia, which portrayed both North and South America as separate from Asia and entirely encircled by water. An accompanying inset in that work went further by explicitly placing the Americas to the east of Asia and showing an intervening ocean, rather than merely positioning them at opposite edges of a projection. In the book Cosmographiae Introductio that accompanied the map, Waldseemüller argued for a fourfold division of the inhabited world and applied the name “America” to part of South America in honor of Amerigo Vespucci, thereby institutionalizing the toponym on European maps.

Beyond four continents

Ancient and non‑Western cosmographies conceived the inhabited world in schemes that diverge markedly from modern Western practice. Vedic literature already envisaged a multi‑part world: passages in the Rigveda (commonly dated to the second millennium BCE) describe the earth as divided into seven regions, and later Hindu Purāṇic texts elaborate a systematic sevenfold geography centered on an enormous sacred mountain, Mount Meru. In these maps the terrestrial regions are arrayed as concentric rings around Meru, which traditional cartographic and textual practice locates approximately in the Himalayan zone, thereby linking cosmological symbolism with specific highland geography.

European mapping and classificatory practice evolved as empirical knowledge expanded. Seventeenth‑century charts such as Joan Blaeu’s Hollandia Nova (based on Tasman and Jansz) began to incorporate southern landmasses, but no single continental schema dominated Western cartography: a fourfold division of the known world persisted well into the nineteenth century, even as some geographers from the late eighteenth century onward treated North and South America as separate entities, producing five‑part models.

The recognition of Australia and Antarctica further altered continental reckonings. European contact with the Australian landmass began in 1606; it was variously regarded as an extension of Asia or as a distinct land until the late eighteenth and nineteenth centuries when arguments for continental status grew stronger. In Anglo‑American geography the mid‑twentieth century saw a terminological shift that stabilized Australia (rather than the broader region termed Oceania) as the continent. Antarctica entered Western atlases in the nineteenth century after its first sighting (1820) and exploratory descriptions (including Charles Wilkes in 1838); however, consistent depiction of Antarctica as a continent in world atlases generally did not occur until after World War II.

The Western continent model became globally influential in the nineteenth and twentieth centuries and was integrated into political and cultural identities—examples include Meiji Japan’s adoption of an “Asian” self‑identification and later nationalist usages in China and Vietnam. Yet continental classification has never been purely physical. Transatlantic cartographic practice diverged: many mid‑nineteenth‑century U.S. atlases treated North and South America as separate, while many European works continued to present the Americas as a single landmass; by the 1950s the two‑Americas model had become standard among U.S. geographers, contributing to a seven‑continent scheme that included Antarctica.

Regional and conceptual alternatives persist. Latin American scholars and educators often prefer a single continental unit, “América,” spanning both North and South America, yielding a six‑continent framework when combined with other conventional units. Conversely, some scholars advocate merging Europe and Asia into “Eurasia,” producing another variant six‑continent arrangement. These enduring differences underline that continental boundaries are as much cultural and conceptual constructs as they are reflections of physical geography.

Geology

Continental crust is composed largely of metamorphic and igneous rocks with a dominantly granitic composition; it is substantially thicker and less dense than the basaltic crust of ocean basins. This lower density causes continental blocks to be buoyantly supported on the mantle, producing the elevated continental platforms that contrast with the deep surrounding oceans.

Many definitions of “continent” emphasize crust built around stable, long‑lived cores called cratons. Cratons have escaped major orogenic reworking since the Precambrian and therefore conserve some of Earth’s oldest lithologies. A typical craton consists of a shield, where ancient crystalline basement is exposed at the surface (commonly 1.5–3.8 billion years old), and a peripheral platform in which the same basement is buried beneath younger sedimentary cover.

Continental lithosphere behaves as an accretionary, non‑recycled “raft”: unlike oceanic basaltic crust, continental crust is rarely consumed wholesale by subduction. This relative preservation underlies the great antiquity of rocks preserved within cratons. Continental growth and modification occur at margins, which are classified as active or passive. Active margins—sites of continent–continent collision or oceanic subduction—are loci of mountain building and continental growth through the accretion of island arcs, microcontinents and other buoyant fragments, producing orogenic belts. Passive margins form where continental lithosphere has been stretched and thinned, creating broad shelves and gradual sediment‑covered slopes that merge into oceanic crust; many passive margins later become active when adjacent oceanic plates cool, densify and begin to subduct beneath the continent.

Plate tectonic motion of a limited set of major plates—commonly described as sixteen principal plates—drives the continual assembly, breakup and reassembly of continental masses. This tectonic cycling produces numerous continental fragments and microcontinents: bodies of continental affinity that lack a major cratonic core. Examples include Zealandia (including New Zealand and New Caledonia), Madagascar, and parts of the northern Mascarene Plateau (including the Seychelles), and several largely granitic Caribbean islands may also be regarded as continental fragments depending on criteria.

The boundary between island and microcontinent is not always clear because continental regions may contain both granitic and volcanic crust. The Kerguelen Plateau, though largely volcanic, is treated as a microcontinental fragment tied to Gondwana breakup; by contrast, purely volcanically constructed islands such as Iceland and Hawaii are not classified as microcontinents. Similarly, several modern landmasses (for example the British Isles, Sri Lanka, Borneo and Newfoundland) occupied marginal positions on former continents such as Laurasia and were isolated by inundation of continental margins.

The long‑term pattern of continental assembly and dispersal is described by the Wilson Cycle, which has produced repeated supercontinents. Columbia (Nuna) assembled around 2.0–1.8 billion years ago and fragmented by about 1.5–1.3 billion years ago; Rodinia formed approximately 1.0 billion years ago and broke into several fragments by ~600 million years ago; those fragments later reassembled as Pangaea, which ultimately separated into Laurasia (forerunner of North America and Eurasia) and Gondwana (the precursor to the remaining continents).

Criticism

Martin W. Lewis argues that commonly used macro-spatial categories—continents, regions and subregions—are not neutral reflections of the Earth’s physical organization but historically contingent constructs. In The Myth of Continents he situates these categories within what he terms “metageography”: the set of implicit spatial assumptions, labels and classificatory schemes through which societies carve up and make sense of the world. Metageographic frameworks condition scholarly inquiry, pedagogy and governance by naturalizing particular territorial divisions and thereby obscuring their origins.

The shaping of metageographic categories, Lewis contends, results from specific historical processes rather than from geological necessity. Colonial expansion, imperial administration, cartographic conventions, linguistic and intellectual traditions, trade and diplomacy, and the bureaucratic needs of institutions have all contributed to fixing certain place-names and boundaries into durable cognitive maps. As a consequence, many regional delimitations do not coincide with physical-geographic entities such as tectonic plates, drainage basins or coherent biogeographic zones; cultural-political regionhood often diverges markedly from geophysical continuities.