Short answers, pulled from the story.
Martin Waldseemüller published the first map to name America as a continent in 1507. This map, titled Universalis Cosmographia, depicted the Americas as a distinct landmass separated from Asia by a vast ocean. The publication marked the moment the concept of a continent shifted from a vague geographical idea to a concrete reality.
Ancient Greek thinkers like Herodotus recognized three continents in the 5th century BCE: Europe, Asia, and Africa. Herodotus questioned this division, noting that he could not conceive why three names should be given to a tract that was in reality one. The boundaries between these continents were not fixed, with early geographers drawing lines from the Black Sea along the Rioni River in Georgia or placing the border at the Don River in Russia.
Zealandia was officially recognized as the eighth continent in 2017. This submerged landmass, primarily located in New Zealand and New Caledonia, contains Precambrian rocks that are twice as old as previously thought. The recognition supports its status as a geological continent based on criteria such as elevation relative to the ocean floor and crust thickness.
Most English-speaking countries teach the seven-continent model as the standard geographical definition, including Australia, Canada, the United Kingdom, and the United States. This model is also taught in countries such as Bangladesh, China, India, Indonesia, Pakistan, the Philippines, Sri Lanka, and Suriname. The seven-continent model lists Asia, Africa, North America, South America, Antarctica, Europe, and Australia as the primary landmasses.
Geologists define a continent by four key criteria: elevation relative to the ocean floor, a wide range of rock types, a crust thicker than the surrounding oceanic crust, and well-defined limits around a large enough area. This definition focuses on physical properties such as metamorphic and igneous rocks of granitic composition that are less dense and much thicker than oceanic crust. The geological definition provides a more objective basis for understanding the Earth's landmasses than cultural or political definitions.