Short answers, pulled from the story.
The number of continents varies from as few as four to as many as seven. Most English-speaking countries recognize seven: Asia, Africa, North America, South America, Antarctica, Europe, and Australia. Fewer-continent models merge regions, such as Eurasia, the Americas, or Afro-Eurasia.
Asia and Europe sit on the continuous landmass of Eurasia but are kept apart for historical and cultural reasons. Europe is treated as a continent with about 10,180,000 square kilometres, while the Indian subcontinent, less than half that area, is called a subcontinent. Some view the Asia-Europe split as a residue of Eurocentrism.
Martin Waldseemüller named America in his 1507 book Cosmographiae Introductio, after Amerigo Vespucci's first name, placing the word on South America. His map Universalis Cosmographia was the first to show North and South America separated from Asia by water.
A continent is one of Earth's major landmasses, including dry land and continental shelves. Microcontinents are small continental fragments, such as Madagascar, that have rifted from a main landmass but are excluded from the continents because of their relatively small size.
Antarctica was sighted in 1820 during the First Russian Antarctic Expedition and described as a continent by Charles Wilkes in 1838 on the United States Exploring Expedition. It was the last continent identified, and an 1849 atlas labelled it a continent, though few atlases followed until after World War II.
Geologists define a continent by continental crust and four criteria: elevation above the ocean floor, a range of igneous, metamorphic, and sedimentary rocks rich in silica, a crust thicker than oceanic crust, and clear limits around an area over one million square kilometres. With Zealandia added in 2017, Earth has seven recognized geological continents.