Studies of rocks found in ancient areas of North America have revealed the oldest known pieces of the continents began to form nearly four billion years ago, soon after Earth itself formed. Geologists believe the interaction of the plates, a process called plate tectonics, contributed to the creation of continents. Today, tectonic plates continue to slowly slide around the surface, just as they have been doing for hundreds of millions of years. The heat from inside Earth causes the plates to slide around on the molten mantle. The crust and the top portion of the mantle form a rigid shell around Earth that is broken up into huge sections called tectonic plates. Eventually, Earth came to have three main layers: the core, the mantle, and the crust. Heavier material sank toward Earth’s center. As the heat increased, some of Earth’s rocky materials melted and rose to the surface, where they cooled and formed a crust. The continuous smashing of space debris and the pull of gravity made Earth's core heat up. Building the Continents Earth formed 4.6 billion years ago from a great, swirling cloud of dust and gas. An imaginary line, running from the northern Ural Mountains in Russia south to the Caspian and Black Seas, separates Europe, to the west, from Asia, to the east. Because of this, most geographers divide Eurasia into Europe and Asia. But linguistically and ethnically, the areas of Asia and Europe are distinct. The continents of Europe and Asia, for example, are actually part of a single, enormous piece of land called Eurasia. To geographers, continents are also culturally distinct. A continental shelf is part of the ocean, but also part of the continent. A continental shelf is a gently sloping area that extends outward from the beach far into the ocean. Continents are defined by their continental shelves. Coastlines, however, do not indicate the actual boundaries of the continents. Asia, the largest continent, has the longest series of coastlines. All continents border at least one ocean. The area of the ocean is more than double the area of all the continents combined. The ocean covers almost three-fourths of Earth. A very small portion of the total land area is made up of islands that are not considered physical parts of continents. Continents make up most-but not all-of Earth’s land surface. Together, the continents add up to about 148 million square kilometers (57 million square miles) of land. Greenland and all the islands in the Caribbean Sea are usually considered part of North America. Japan, for instance, is part of the continent of Asia. When geographers identify a continent, they usually include all the islands associated with it. The continents are, from largest to smallest: Asia, Africa, North America, South America, Antarctica, Europe, and Australia. A continent is one of Earth’s seven main divisions of land.
0 Comments
Leave a Reply. |
Details
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |