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The exosphere is a thin, atmosphere-like volume surrounding a planet or natural satellite where molecules are gravitationally bound to that body, but where the density is so low that the molecules are essentially collision-less. [1]
The height of the thermopause varies considerably due to changes in solar activity. [16] Because the thermopause lies at the lower boundary of the exosphere, it is also referred to as the exobase. The lower part of the thermosphere, from 80 to 550 kilometres (50 to 342 mi) above Earth's surface, contains the ionosphere.
An atmosphere (from Ancient Greek ἀτμός (atmós) 'vapour, steam' and σφαῖρα (sphaîra) 'sphere') [1] is a layer of gases that envelop an astronomical object, held in place by the gravity of the object. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low.
The mean height of land above sea level is 686 m (2,250 ft). [29] The geological history of Earth can be broadly classified into two periods namely: Precambrian: extends for approximately 90% of geologic time, from 4.6 billion years ago to the beginning of the Cambrian Period (539 Ma).
This glossary of geography terms is a list of definitions of terms and concepts used in geography and related fields, including Earth science, oceanography, cartography, and human geography, as well as those describing spatial dimension, topographical features, natural resources, and the collection, analysis, and visualization of geographic ...
Curiously, the labels for Africa and Europe are reversed, with Europe scribed in red and gold as 'Africa', and vice versa. An open-access high-resolution digital image of the map with more than 1,000 place and name annotations is included among the thirteen medieval maps of the world edited in the Virtual Mappa project.
Map showing the extent of Mesopotamia. The geography of Mesopotamia, encompassing its ethnology and history, centered on the two great rivers, the Tigris and Euphrates.While the southern is flat and marshy, the near approach of the two rivers to one another, at a spot where the undulating plateau of the north sinks suddenly into the Babylonian alluvium, tends to separate them still more ...
Hoodoos in Bryce Canyon National Park, Utah. A hoodoo (also called a tent rock, fairy chimney, or earth pyramid) is a tall, thin spire of rock formed by erosion.Hoodoos typically consist of relatively soft rock topped by harder, less easily eroded stone that protects each column from the elements.