Instead, most of the hydrogen loss comes from the destruction of methane in the upper atmosphere. [citation needed], The first human to orbit Earth was Yuri Gagarin on 12 April 1961. [132], 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. The orbital and axial planes are not precisely aligned: Earth's axis is tilted some 23.44 degrees from the perpendicular to the Earth–Sun plane (the ecliptic), and the Earth–Moon plane is tilted up to ±5.1 degrees against the Earth–Sun plane. [248][249] Normally, the only humans in space are those on the International Space Station. Naturally, there are some deviations in the local topography where objects located away from the equator are closer or father away from the center of the Earth than others in the same region. San Francisco's climate is significantly more moderate as the prevailing wind direction is from sea to land. [70][71] The earliest direct evidence of life on Earth is contained in 3.45 billion-year-old Australian rocks showing fossils of microorganisms. [193] Above the Arctic Circle and below the Antarctic Circle there is no daylight at all for part of the year, causing a polar night, and this night extends for several months at the poles themselves. 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. Because of this, the diameter of the Earth at the equator is about 43 kilometers (27 mi) larger than the pole-to-pole diameter. Please refresh the page and try again. The presence of grains of the mineral zircon of Hadean age in Eoarchean sedimentary rocks suggest that at least some felsic crust existed as early as 4.4 Ga, only 140 Ma after Earth's formation. Humans increasingly impact Earth's hydrology, atmospheric processes and other life..mw-parser-output .toclimit-2 .toclevel-1 ul,.mw-parser-output .toclimit-3 .toclevel-2 ul,.mw-parser-output .toclimit-4 .toclevel-3 ul,.mw-parser-output .toclimit-5 .toclevel-4 ul,.mw-parser-output .toclimit-6 .toclevel-5 ul,.mw-parser-output .toclimit-7 .toclevel-6 ul{display:none}, The modern English word Earth developed, via Middle English,[n 6] from an Old English noun most often spelled eorðe. [192], The axial tilt of Earth is approximately 23.439281°[2] with the axis of its orbit plane, always pointing towards the Celestial Poles. Because Earth's solar day is now slightly longer than it was during the 19th century due to tidal deceleration, each day varies between 0 and 2 SI ms longer than the mean solar day. See: Due to natural fluctuations, ambiguities surrounding, This is the measurement taken by the vessel, The ultimate source of these figures, uses the term "seconds of UT1" instead of "seconds of mean solar time".—. Earth is the densest planet in the Solar System and the largest and most massive of the four rocky planets. [n 17][141], The average salinity of Earth's oceans is about 35 grams of salt per kilogram of sea water (3.5% salt). [182], Earth's rotation period relative to the Sun—its mean solar day—is 86,400 seconds of mean solar time (86,400.0025 SI seconds). [216], A planet that can sustain life is termed habitable, even if life did not originate there. These dates change over time due to precession and other orbital factors, which follow cyclical patterns known as Milankovitch cycles. [171], The gravity of Earth is the acceleration that is imparted to objects due to the distribution of mass within Earth. Earth is the largest of the terrestrial planets of the inner solar system, bigger than Mercury, Venus and Mars. "[33], Occasionally, the name Terra /ˈtɛrə/ is used in scientific writing and especially in science fiction to distinguish our inhabited planet from others,[34] while in poetry Tellus /ˈtɛləs/ has been used to denote personification of the Earth. [233] Many places are subject to earthquakes, landslides, tsunamis, volcanic eruptions, tornadoes, sinkholes, blizzards, floods, droughts, wildfires, and other calamities and disasters. [63], Chemical reactions led to the first self-replicating molecules about four billion years ago. Photosynthesis provided a source of free oxygen, but the loss of reducing agents such as hydrogen is thought to have been a necessary precondition for the widespread accumulation of oxygen in the atmosphere. The mean height of land above sea level is about 797 m (2,615 ft). A half billion years later, the last common ancestor of all current life arose. Thanks to improvements made in the field of astronomy by the 17th and 18th centuries  – as well as geodesy, a branch of mathematics dealing with the measurement of the Earth – scientists have learned that the Earth is not a perfect sphere. ", "Curious Kids: Why is the moon called the moon? [n 3] Earth's largest artificial satellite is the International Space Station. When atmospheric conditions permit an uplift of warm, humid air, this water condenses and falls to the surface as precipitation. [91][92][93][94] The average diameter of the reference spheroid is 12,742 kilometres (7,918 mi). [citation needed], Earth's human population passed seven billion in the early 2010s,[237] and is projected to peak at around ten billion in the second half of the 21st century. [52] By 3.5 Ga, Earth's magnetic field was established, which helped prevent the atmosphere from being stripped away by the solar wind. This is the diameter of the Earth measured from one side of the Earth, passing through the center. [200][201] The natural satellites of other planets are also referred to as "moons", after Earth's. [35] The Greek poetic name Gaea (Gæa) /ˈdʒiːə/ is rare, though the alternative spelling Gaia has become common due to the Gaia hypothesis, in which case its pronunciation is /ˈɡaɪə/ rather than the more Classical /ˈɡeɪə/.[36]. The combination of these processes recycles the oceanic crust back into the mantle.

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