Continent Europe and Asia together as a single continent, dubbed "Eurasia". In this model, the world is divided into six continents, with North America and South America considered separate continents. Geologists use the term "continent" in a different manner from geographers. In geology a continent is defined by continental crust: a platform of metamorphic and igneous rock, largely of granitic composition. Some geologists restrict the term 'continent' to portions of the crust built around stable Precambrian "shield", typically 1.5 to 3.8 billion years old, called a craton. The craton itself is an accretionary complex of ancient mobile belts (mountain belts) from
Largest organisms over . The largest organism in the world, according to mass, is the aspen tree whose colonies of clones can grow up to five miles long. The largest such colony is Pando, in the Fishlake National Forest in Utah. Another form of flowering plant that rivals Pando as the largest organism on earth in breadth, if not mass, is the giant marine plant, "Posidonia oceanica", discovered in the Mediterranean near the Balearic Islands, Spain. Its length is about . It may also be the oldest living organism in the world, with an estimated age of 100,000 years. Green algae are