Earth System

The Continents

A continent is usually regarded as a large unbroken land mass completely surrounded by water, although some are not. There are several continent models, two of which are depicted in Figure 2.15 The seven continents model of  North America, South America, Europe, Asia, Africa, Australia, and Antarctica are defined by physical and cultural conventions. Considered a separate continent in the seven continent model, Europe is a physical extension of Asia, together called  the "Eurasian continent" in the six continent model. The Ural and the Caucasus mountains are used as the boundary between Europe and Asia. The island groups of the Pacific are grouped together as Oceania but are not parts of an actual continent. 

Seven
                      contiinents

Figure 2.15a Seven Continent Model
(Courtesy Wikipedia)

Six continents


Figure 2.15b Six Continent Model
(Courtesy Wikipedia)

Geologists view continents in a different way from geographers, a continent is defined as a portion of the fractured Earth's crust. Continental crust is composed primarily of granitic rock while oceanic crust is mostly basaltic rock. These fractured pieces are called "tectonic" or "lithospheric plates".

Tectonic Plates

Figure 2.16 Earth's Tectonic Plates
Courtesy USGS

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