Continent Continent A continent is one of several very large landmasses of the world. Generally identified by convention rather than any strict criteria, up to seven regions are commonly regarded as continents. Ordered from largest in area to smallest, they are: Asia, Africa, North America, South America, Antarctica, Europe, and Australia. Geologically, the continents largely correspond to areas of continental crust that are found on the continental plates. However, some areas of continental crust are regions covered with water not usually included in the list of continents. Zealandia is one such area (see submerged continents below). Islands are frequently grouped with
Smallest organisms 3.5 kilo base pairs (kb) and particle diameters of 80 nanometres (nm). The smallest double stranded DNA viruses are the hepadnaviruses such as Hepatitis B, at 3.2 kb and 42 nm; parvoviruses have smaller capsids, at 18-26 nm, but larger genomes, at 5 kb. It is important to consider other self replicating genetic elements, such as satelliviruses, viroids and ribozymes. The genome of "Nasuia deltocephalinicola", a symbiont of the European pest leafhopper, Macrosteles quadripunctulatus consists of a circular chromosome of 112,031 base pairs. "Nanoarchaeum equitans"'s genome is 490,885 nucleotides long. "Pelagibacter ubique" is one of the smallest known free-living bacterium