[229] Many places are subject to earthquakes, landslides, tsunamis, volcanic eruptions, tornadoes, blizzards, floods, droughts, wildfires, and other calamities and disasters. The elevation of the land surface varies from the low point of −418 m (−1,371 ft) at the Dead Sea, to a maximum altitude of 8,848 m (29,029 ft) at the top of Mount Everest. Earth's atmosphere consists mostly of nitrogen and oxygen. [217], Thermal energy causes some of the molecules at the outer edge of the atmosphere to increase their velocity to the point where they can escape from Earth's gravity. Earth bound events are often taken for granted since we live here, but, with a little research, you may find much more excitement outside of your back door than you ever expected. [72][73] The earliest direct evidence of life on Earth is contained in 3.45 billion-year-old Australian rocks showing fossils of microorganisms. [233], Earth's human population passed seven billion in the early 2010s,[235] and is projected to peak at around ten billion in the second half of the 21st century. The Australian Plate fused with the Indian Plate between 50 and 55 Ma. The first continental crust, which was more felsic in composition, formed by the partial melting of this mafic crust. [115][116], The mean heat loss from Earth is 87 mW m−2, for a global heat loss of 4.42×1013 W.[117] A portion of the core's thermal energy is transported toward the crust by mantle plumes, a form of convection consisting of upwellings of higher-temperature rock. And More…, Episode 688: Remnants From the Early Universe. That is pretty uncommon in our Solar System. By 2050, 68% of the world's population is expected to be living in urban, rather than rural, areas. The outer layer is a chemically distinct silicate solid crust, which is underlain by a highly viscous solid mantle. When atmospheric conditions permit an uplift of warm, humid air, this water condenses and falls to the surface as precipitation. The oceans cover an area of 361.8 million km2 (139.7 million sq mi) with a mean depth of 3,682 m (12,080 ft), resulting in an estimated volume of 1.332 billion km3 (320 million cu mi). From Earth itself comes earthly. [193] The oceans are also a reservoir of dissolved atmospheric gases, which are essential for the survival of many aquatic life forms. Earth's polar radius is 3,950 miles (6,356 km) — a difference of 13 miles (22 km). [224] Estimates of the number of species on Earth today vary; most species have not been described. [104], The most common rock constituents of the crust are nearly all oxides: chlorine, sulphur, and fluorine are the important exceptions to this and their total amount in any rock is usually much less than 1%. [167][n 19] Because the Southern Hemisphere is tilted toward the Sun at about the same time that Earth reaches the closest approach to the Sun, the Southern Hemisphere receives slightly more energy from the Sun than does the northern over the course of a year. See no ads on this site, see our videos early, special bonus material, and much more. [134][135], The pedosphere is the outermost layer of Earth's continental surface and is composed of soil and subject to soil formation processes. [213] Surface air temperature can rise to around 55 °C (131 °F) in hot deserts, such as Death Valley, and can fall as low as −89 °C (−128 °F) in Antarctica. As of 4 January 2018, the United States Strategic Command tracked a total of 18,835 artificial objects, mostly debris. This hypothesis explains (among other things) the Moon's relative lack of iron and volatile elements and the fact that its composition is nearly identical to that of Earth's crust. [69] Among the earliest fossil evidence for life is microbial mat fossils found in 3.48 billion-year-old sandstone in Western Australia,[70] biogenic graphite found in 3.7 billion-year-old metasedimentary rocks in Western Greenland,[71] and remains of biotic material found in 4.1 billion-year-old rocks in Western Australia. The Earth only has one moon. The combination of these processes recycles the oceanic crust back into the mantle. Local topography deviates from this idealized spheroid, although on a global scale these deviations are small compared to Earth's radius: the maximum deviation of only 0.17% is at the Mariana Trench (10,925 metres or 35,843 feet below local sea level),[98] whereas Mount Everest (8,848 metres or 29,029 feet above local sea level) represents a deviation of 0.14%. Earth is the third planet from the Sun and the only astronomical object known to harbor life. [200] Each layer has a different lapse rate, defining the rate of change in temperature with height. There was a problem. The station's crew, made up of six people, is usually replaced every six months. [128] Below the ocean's surface are much of the continental shelf, mountains, volcanoes,[94] oceanic trenches, submarine canyons, oceanic plateaus, abyssal plains, and a globe-spanning mid-ocean ridge system. Other notable plates include the Arabian Plate, the Caribbean Plate, the Nazca Plate off the west coast of South America and the Scotia Plate in the southern Atlantic Ocean. From Greek Gaia and Gaea comes Gaian and Gaean. [242][243], The first human to orbit Earth was Yuri Gagarin on 12 April 1961. Some geological evidence indicates that life may have arisen as early as 4.1 billion years ago. Since then, the combination of Earth's distance from the Sun, physical properties and geological history have allowed life to evolve and thrive. In geodesy, the exact shape that Earth's oceans would adopt in the absence of land and perturbations such as tides and winds is called the geoid. "[35], Occasionally, the name Terra /ˈtɛrə/ is used in scientific writing and especially in science fiction to distinguish our inhabited planet from others,[36] while in poetry Tellus /ˈtɛləs/ has been used to denote personification of the Earth. Earth is sometimes personified as a deity. [5], The Moon and Earth orbit a common barycenter every 27.32 days relative to the background stars. [93] To second order, Earth is approximately an oblate spheroid, whose equatorial diameter is 43 kilometres (27 mi) larger than the pole-to-pole diameter. Those numbers tell you the size of the Earth, but what about its other statistics? The modern English word Earth developed, via Middle English,[n 6] from an Old English noun most often spelled eorðe. Objects must orbit Earth within this radius, or they can become unbound by the gravitational perturbation of the Sun. Want more resources on the Earth? A nebula contains gas, ice grains, and dust (including primordial nuclides). [247] The farthest that humans have traveled from Earth is 400,171 km (248,655 mi), achieved during the Apollo 13 mission in 1970.