The Ultimate Continental Challenge

Continents are large geographical regions identified by convention rather than strict criteria, and the number of continents varies from four to seven depending on the model used. The seven-continent model includes Asia, Africa, North America, South America, Antarctica, Europe, and Australia. Oceanic islands are frequently grouped with a nearby continent to divide all the world's land into geographical regions, and the geological continents correspond to seven large areas of continental crust found on tectonic plates. The idea of continental drift postulates that the current continents formed from the breaking up of a supercontinent (Pangaea) that formed hundreds of millions of years ago. The criterion that each continent is a discrete landmass is commonly relaxed due to historical conventions and practical use, and the edge of the continental shelf is considered the true edge of the continent. Some areas of continental crust are largely covered by the ocean and may be considered submerged continents, while some islands lie on sections of continental crust that have rifted and drifted apart from a main continental landmass and may be considered microcontinents. Geologists use four key attributes to define a continent: high elevation, a great thickness of continental crust, a relatively low density of crustal material, and a broad area. Earth currently has seven usually-recognized geological continents: Africa, Antarctica, Australia, Eurasia, North America, South America, and Zealandia. The term "continent" translates the Greek word ἤπειρος, meaning "landmass, terra firma", and the first distinction between continents was made by ancient Greek mariners who gave the names Europe and Asia to the lands on either side of the waterways of the Aegean Sea.The History and Definition of Continents

• The ancient Greeks believed in three continents: Europe, Asia, and Libya (Africa).
• The Isthmus of Suez was used as the boundary between Asia and Africa, but some writers continued to consider it the Nile or the western border of Egypt.
• Christopher Columbus sailed to the Caribbean in 1492, but he never believed he had reached a new continent.
• Amerigo Vespucci and Gonçalo Coelho sailed around the southern end of the Asian mainland into the Indian Ocean, passing through Fernando de Noronha. After reaching the coast of Brazil, they confirmed that it was a land of continental proportions.
• The name "New World" began appearing as a name for South America on world maps, but maps of this time still showed North America connected to Asia and showed South America as a separate land.
• Martin Waldseemüller published a world map in 1507, which was the first to show North and South America as separate from Asia and surrounded by water.
• The term "continent" was derived from the Latin terra continens and referred to "a connected or continuous tract of land" or mainland.
• Some geographers started to regard North and South America as two parts of the world, making five parts in total, but the fourfold division prevailed well into the 19th century.
• Some geographers considered Australia a continent in its own right, making it the sixth or fifth continent.
• Antarctica was sighted in 1820 and described as a continent by Charles Wilkes in 1838, the last continent identified.
• Geologists use the term continent to define continental crust, which is a platform of metamorphic and igneous rock, largely of granitic composition.
• The movement of plates has caused the continual formation and breakup of continents, and occasionally supercontinents, in a process called the Wilson Cycle.