Earth

Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets. It is sometimes referred to as the world, the Blue Planet, or by its Latin name, Terra.

Earth formed approximately 4.54 billion years ago, and life appeared on its surface within one billion years. Earth's biosphere then significantly altered the atmospheric and other basic physical conditions, which enabled the proliferation of organisms as well as the formation of the ozone layer, which together with Earth's magnetic field blocked harmful solar radiation, and permitted formerly ocean-confined life to move safely to land. The physical properties of the Earth, as well as its geological history and orbit, have allowed life to persist. Estimates on how much longer the planet will be able to continue to support life range from 500 million years (myr), to as long as 2.3 billion years (byr).

Earth's crust is divided into several rigid segments, or tectonic plates, that migrate across the surface over periods of many millions of years. About 71% of the surface is covered by salt water oceans, with the remainder consisting of continents and islands which together have many lakes and other sources of water that contribute to the hydrosphere. Earth's poles are mostly covered with ice that is the solid ice of the Antarctic ice sheet and the sea ice that is the polar ice packs. The planet's interior remains active, with a solid iron inner core, a liquid outer core that generates the magnetic field, and a thick layer of relatively solid mantle.

Earth interacts with other objects in space, especially the Sun and the Moon. During one orbit around the sun, the Earth rotates about its own axis 366.26 times, creating 365.26 solar days, or one sidereal year. The Earth's axis of rotation is tilted 23.4° away from the perpendicular of its orbital plane, producing seasonal variations on the planet's surface with a period of one tropical year (365.24 solar days). The Moon is Earth's only natural satellite. It began orbiting the Earth about 4.53 billion years ago (bya). The Moon's gravitational interaction with Earth stimulates ocean tides, stabilizes the axial tilt, and gradually slows the planet's rotation.

The planet is home to millions of species, including humans. Both the mineral resources of the planet and the products of the biosphere contribute resources that are used to support a global human population. These inhabitants are grouped into about 200 independent sovereign states, which interact through diplomacy, travel, trade, and military action. Human cultures have developed many views of the planet, including its personification as a planetary deity, its shape as flat, its position as the center of the universe, and in the modern Gaia Principle, as a single, self-regulating organism in its own right.

Read more about Earth:  Name and Etymology, Composition and Structure, Moon, Habitability, Cultural Viewpoint

Other articles related to "earth":

Persephone - Greek Mythology - Abduction Myth
... a field when Hades came to abduct her, bursting through a cleft in the earth ... when she found her daughter had disappeared, searched for her all over the earth with torches ... In most versions she forbids the earth to produce, or she neglects the earth and in the depth of her despair she causes nothing to grow ...
Gravitational Constant - The GM Product
... and the mass of a given astronomical body such as the Sun or the Earth—is known as the standard gravitational parameter and is denoted ... Also, for celestial bodies such as the Earth and the Sun, the value of the product GM is known more accurately than each factor independently ... For Earth, using M⊕ as the symbol for the mass of the Earth, we have Calculations in celestial mechanics can also be carried out using the unit of solar ...
Earth - Cultural Viewpoint
... Main article Earth in culture The standard astronomical symbol of the Earth consists of a cross circumscribed by a circle ... in the Solar System, humankind did not begin to view the Earth as a moving object in orbit around the Sun until the 16th century ... Earth has often been personified as a deity, in particular a goddess ...
2004 AS1
... by the temporary name AL00667, is a near-Earth asteroid, first discovered on January 13, 2004, by the LINEAR project ... web by the Minor Planet Center (MPC) suggesting an imminent collision with Earth on or about January 15 with a likelihood of 14 ... a distance of 12 Gm (or 32 times the distance from the Earth to the Moon), posing no threat ...
2004 FH
2004 FH is a near-Earth asteroid that was discovered on March 15, 2004, by the NASA-funded LINEAR asteroid survey ... is roughly 30 metres in diameter and passed just 43,000 km (27,000 mi) above the Earth's surface on March 18, 2004, at 2208 UTC making it the 11th closest approach to ... it is still the fourth largest asteroid detected coming closer to the Earth than the Moon ...

Famous quotes containing the word earth:

    For sounds in winter nights, and often in winter days, I heard the forlorn but melodious note of a hooting owl indefinitely far; such a sound as the frozen earth would yield if struck with a suitable plectrum, the very lingua vernacula of Walden Wood, and quite familiar to me at last, though I never saw the bird while it was making it.
    Henry David Thoreau (1817–1862)

    True, that true beauty virtue is indeed,
    Whereof this beauty can be but a shade,
    Which elements with mortal mixture breed.
    True, that on earth we are but pilgrims made,
    And should in soul up to our country move.
    True, and yet true that I must Stella love.
    Sir Philip Sidney (1554–1586)

    We seem to think that the earth must go through the ordeal of sheep-pasturage before it is habitable by man.
    Henry David Thoreau (1817–1862)