The world is made up of several large landmasses. By tradition, seven of these masses are known as continents; these are Asia, Africa, North America, South America, Antarctica, Europe and Australia.

For the purpose of dividing the world up into geopolitical regions, small landmasses of islands are grouped with nearby continents. For example, most of the island countries and territories in the Pacific Ocean are generally considered to be part of the continent of Australia, which is sometimes known as Oceania. Under the same construct, the islands of Great Britain, Ireland, Malta and Iceland are deemed part of Europe. Madagascar is viewed as part of Africa.

Of the seven generally recognized continents, only Antarctica and Australia are wholly separated from other continents by an ocean. Asia and Africa are joined by the Isthmus of Suez, and North and South America are joined by the Isthmus of Panama, not considering the Suez Canal and the Panama Canal, which are artificial constructs. Of course, Europe and Asia are not separated by water, but are viewed as separate continents because of other physical features, as well as bodies of water, that mark their boundaries; these include the Caucasus Mountains, the Black Sea, and the Caspian Sea.

Not everyone agrees with the eight-continent scheme. Europe and Asia are sometimes considered to be one continent, known as Eurasia, while North America, Central America, and South America might be considered one continent. If continents were defined strictly as distinct landmasses, then Africa, Asia, and Europe would be considered one continent as well, giving us a four-continent model of the earth. Various models include the four-continent model (Afro-Eurasia, America, Antarctica, Australia), a five-continent model (Africa, Eurasia, America, Antarctica, Australia), two six-continent models (Africa, Asia, Europe, America, Antarctica, Australia; and Africa, Eurasia, North America, South America, Antarctica, Australia/Oceania), and a seven-continent model (Africa, Asia, Europe, North America, South America, Antarctica, Australia/Oceania).

In the history of the earth, however, there have been times when continents, now separated by broad stretches of ocean, had land bridges connecting them. Paleontologists deduce, from the occurrence of identical species in different parts of the world, that these landmasses were once connected. Even within the history of mankind, it has been suggested that the Americas were populated at a time when Alaska was connected to Russia by a land bridge. The similarities between species in parts of the world separated by ocean leave little doubt that many of the continents were once connected in some way.

One theory is that of land bridges, as discussed above. Another is the occurrence of a continental drift. Proponents of this theory argue that the continents shifted at some point or points within the history of the planet. South America was once positioned alongside Africa, forming a unified block that was split in two during the Cretaceous period, becoming increasingly separated over millions of years. A brief look at a map shows that these two blocks are congruent even today.

In a similar manner, those who believe in the continental drift theory hold that North America was once joined with Europe, forming a coherent block with it and Greenland, at least from Newfoundland and Ireland northwards. This block was first broken in the later Tertiary period and, to the north, as late as the Quaternary, through a forked rift at Greenland. Over time, the land areas drifted further away from one another. Antarctica, Australia, and India were alongside southern Africa, forming, along with South America, a large continent. This block split off by degrees during the Jurassic, Cretaceous, and Tertiary periods, its sub-blocks drifting off in all directions. India was originally joined with Asia through a long stretch of land, much of it under shallow water. India separated from Australia in the early Jurassic, and from Madagascar during the period between the Tertiary and the Cretaceous.

For the purposes of categorization here, we will be grouping the land areas of the earth into seven continents: Africa, Antarctica and the Arctic, Asia, Australia, Europe, North America, and South America. Each of these continents is subcategorized by geopolitical divisions known as countries and smaller divisions, which may be known as states, provinces, and even further, into cities and towns.

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