The EARTH

The EARTH

The Earth is a sphere of 12,756 KM diameter. Light takes 8 minutes and 19 seconds from sun to reach earth.

The gravity of the Sun at the surface is 28 times the gravity of the Earth. If you weighed 100 kg on Earth you would weigh only 17 kg in moon but 2800 kg in sun. With gravity on the Moon so low, you would be able to jump much higher. If you can jump 1 metre cm on Earth, you would be able to jump almost 6 meters straight up into the air. If you jumped off the roof of a house in moon, it would only feel like you jumped off a table. You would be able to throw a ball 6 times further, hit a golf ball 6 times further etc.

The earth, moon and other planets revolve around their star called Sun. This is called the solar system.

The diameter of the Moon is 3474 km. The average distance from the centre of the Earth to the center of the Moon is 384,403 km. Light travels this distance in 1.2 seconds. Diameter of Sun is 1,390,000 KM. If we are standing at the centre of the Sun, then the surface of sun would be at twice the distance from earth to the moon. Or the Sun is twice as big as the orbit of moon from Erath.  The Sun is 149,597,870 (to 892) KM away from the earth. This is called One Astronomical unit (AU).

The universe originated with a ‘Big Bang’ about 13.7 Billion to 14.7 Billion years ago. The Sun was born 4.6 billion years ago. The Earth and Solar System were born about 4.55 Billion Years ago. The Moon was born 4.527 billion years ago.

The Sun happens to be 400 times the Moon's diameter, and 400 times as far away. That coincidence means the Sun and Moon appear to be the same size when viewed from Earth. The moon goes around the earth at 1.022 KM per second

Some facts:

  

Orbital period - 365.256363004 days

Average orbital speed - 29.78 km/s or 107,200 km/h

Satellites 1 natural (The Moon)

Mean radius - 6,371.0 km

Surface area - 510,072,000 km²

Land (29.2 %);Water (70.8 %)

Escape velocity -11.186 km/s

Sidereal rotation period - 23h 56m 4.100s

Equatorial rotation velocity - 1,674.4 km/h (465.1 m/s)

Atmosphere Composition

78.08% nitrogen (N2); 20.95% oxygen (O2); 0.93% argon

0.038% carbon dioxide; About 1% water vapour (varies with climate)

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

Home to millions of species including humans, Earth is currently the only astronomical body where life is known to exist. The planet formed 4.54 billion years ago, and life appeared on its surface within one billion years. Earth's biosphere has significantly altered the atmosphere and other abiotic conditions on the planet, enabling the proliferation of aerobic organisms as well as the formation of the ozone layer which, together with Earth's magnetic field, blocks harmful solar radiation, permitting life on land. The planet is expected to continue supporting life for at least another 500 million years.

Earth's outer surface 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 with salt water oceans, the remainder consisting of continents and islands which together have many lakes and other sources of water contributing to the hydrosphere. Liquid water, necessary for all known life, is not known to exist in equilibrium on any other planet's surface. Earth's poles are mostly covered with solid ice. The planet's interior remains active, with a thick layer of relatively solid mantle, a liquid outer core that generates a magnetic field, and a solid iron inner core.

Earth interacts with other objects in space, especially the Sun and the Moon. At present, Earth orbits the Sun once every 366.26 times it rotates about its own axis, which is equal to 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). Earth's only known natural satellite, the Moon, which began orbiting it about 4.53 billion years ago, provides ocean tides, stabilizes the axial tilt and gradually slows the planet's rotation. Between approximately 3.8 billion and 4.1 billion years ago, numerous asteroid impacts during the Late Heavy bombardment caused significant changes to the greater surface environment.

Both the mineral resources of the planet, as well as 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 personification as a deity, a belief in a flat Earth or in the Earth as the centre of the universe.

    

Scientists have been able to reconstruct detailed information about the planet's past. The earliest dated Solar System material was formed 4.5672 billion years ago, and by 4.54 billion years ago the Earth and the other planets in the Solar System had formed out of the solar nebula, a disk-shaped mass of dust and gas left over from the formation of the Sun. Initially molten, the outer layer of the planet Earth cooled to form a solid crust when water began accumulating in the atmosphere. The Moon formed shortly thereafter, 4.53 billion years ago.

The current consensus model for the formation of the Moon is the giant impact hypothesis, in which the Moon was created when a Mars-sized object (sometimes called Theia) with about 10% of the Earth's mass impacted the Earth in a glancing blow. In this model, some of this object's mass would have merged with the Earth and a portion would have been ejected into space, but enough material would have been sent into orbit to coalesce into the Moon.

Out gassing and volcanic activity produced the primordial atmosphere of the Earth. Condensing water vapour, augmented by ice and liquid water delivered by asteroids and the larger proto-planets, comets, and trans-Neptunian objects produced the oceans. A combination of greenhouse gases and higher levels of solar activity served to raise the Earth's surface temperature, preventing the oceans from freezing over. By 3.5 billion years ago, the Earth's magnetic field was established, which helped prevent the atmosphere from being stripped away by the solar wind.

Earth is a terrestrial planet, meaning that it is a rocky body, rather than a gas giant like Jupiter. It is the largest of the four solar terrestrial planets in size and mass. Of these four planets, Earth also has the highest density, the highest surface gravity, the strongest magnetic field, and fastest rotation. It also is the only terrestrial planet with active plate tectonics.

The shape of the Earth is very close to that of an oblate spheroid, a sphere flattened along the axis from pole to pole such that there is a bulge around the equator. This bulge results from the rotation of the Earth, and causes the diameter at the equator to be 43 km larger than the pole to pole diameter. The average diameter of the reference spheroid is about 12,742 km.

The largest local deviations in the rocky surface of the Earth are Mount Everest (8848 m above local sea level) and the Mariana Trench (10,911 m below local sea level).

The mass of the Earth is approximately ……….kg. It is composed mostly of iron (32.1%), oxygen (30.1%), silicon (15.1%), magnesium (13.9%), sulphur (2.9%), nickel (1.8%), calcium (1.5%), and aluminium (1.4%); with the remaining 1.2% consisting of trace amounts of other elements. Due to mass segregation, the core region is believed to be primarily composed of iron (88.8%), with smaller amounts of nickel (5.8%), sulphur (4.5%), and less than 1% trace elements.

The interior of the Earth has a distinct outer and inner core. The outer layer of the Earth is a chemically distinct silicate solid crust, which is underlain by a highly viscous solid mantle. The thickness of the crust varies: averaging 6 km under the oceans and 50 km on the continents. The crust and the cold, rigid, top of the upper mantle are collectively known as the lithosphere, and it is of the lithosphere that the tectonic plates are comprised.

Earth's internal heat comes from a combination of residual heat from planetary accretion (about 20%) and heat produced through radioactive decay (80%). The major heat-producing isotopes in the Earth are potassium-40, uranium-238, uranium-235, and thorium-232. At the centre of the planet, the temperature may be up to 7,000 K and the pressure could reach 360 GPa.

The mechanically rigid outer layer of the Earth, the lithosphere, is broken into pieces called tectonic plates. These plates are rigid segments that move in relation to one another at one of three types of plate boundaries: Convergent boundaries, at which two plates come together, Divergent boundaries, at which two plates are pulled apart, and Transform boundaries, in which two plates slide past one another laterally. Earthquakes, volcanic activity, mountain-building, and oceanic trench formation can occur along these plate boundaries.

About 70.8% of the surface is covered by water; The remaining 29.2% not covered by water consists of mountains, deserts, plains, plateaus, and other geomorphologies.

The mass of the oceans is approximately ……….. metric tons, or about 1/4400 of the total mass of the Earth. If all the land on Earth were spread evenly, water would rise to an altitude of more than 2.7 km. About 97.5% of the water is saline, while the remaining 2.5% is fresh water. Most fresh water, about 68.7%, is currently ice.

The average salinity of the Earth's oceans is about 35 grams of salt per kilogram of sea water. Most of this salt was released from volcanic activity or extracted from cool, igneous rocks. The oceans are also a reservoir of dissolved atmospheric gases, which are essential for the survival of many aquatic life forms. Sea water has an important influence on the world's climate, with the oceans acting as a large heat reservoir.

The atmospheric pressure on the surface of the Earth averages 101.325 kPa, with a scale height of about 8.5 km. It is 78% nitrogen and 21% oxygen, with trace amounts of water vapour, carbon dioxide and other gaseous molecules. The height of the troposphere varies with latitude, ranging between 8 km at the poles to 17 km at the equator, with some variation resulting from weather and seasonal factors.

Other atmospheric functions important to life on Earth include transporting water vapour, providing useful gases, causing small meteors to burn up before they strike the surface, and moderating temperature. This last phenomenon is known as the greenhouse effect: trace molecules within the atmosphere serve to capture thermal energy emitted from the ground, thereby raising the average temperature. Carbon dioxide, water vapour, methane and ozone are the primary greenhouse gases in the Earth's atmosphere. Without this heat-retention effect, the average surface temperature would be 18 °C and life would likely not exist.

The Earth's atmosphere has no definite boundary, slowly becoming thinner and fading into outer space. Three-quarters of the atmosphere's mass is contained within the first 11 km of the planet's surface. This lowest layer is called the troposphere. Energy from the Sun heats this layer, and the surface below, causing expansion of the air. This lower density air then rises, and is replaced by cooler, higher density air. The result is atmospheric circulation that drives the weather and climate through redistribution of heat energy.

Water vapour generated through surface evaporation is transported by circulatory patterns in the atmosphere. When atmospheric conditions permit an uplift of warm, humid air, this water condenses and settles to the surface as precipitation. Most of the water is then transported to lower elevations by river systems and usually returned to the oceans or deposited into lakes. This water cycle is a vital mechanism for supporting life on land, and is a primary factor in the erosion of surface features over geological periods.

The amount of solar energy reaching the Earth decreases with increasing latitude. At higher latitudes the sunlight reaches the surface at a lower angles and it must pass through thicker columns of the atmosphere. As a result, the mean annual air temperature at sea level decreases by about 0.4°C per  degree of latitude away from the equator. The Earth can be sub-divided into specific latitudinal belts of approximately homogeneous climate. Ranging from the equator to the Polar Regions, these are the tropical (or equatorial), subtropical, temperate and polar climates. The features and skin colour of the people in these areas also vary according to the sunlight and environment.

Above the troposphere, the atmosphere is usually divided into the stratosphere, mesosphere, and thermosphere. Each layer has a different lapse rate, defining the rate of change in temperature with height. Beyond these, the exosphere thins out into the magnetosphere, where the Earth's magnetic fields interact with the solar wind.

The Karman line, defined as 100 km above the Earth's surface, is a working definition for the boundary between atmosphere and space.

Thermal energy causes some of the molecules at the outer edge of the Earth's atmosphere have their velocity increased to the point where they can escape from the planet's gravity. This results in a slow but steady leakage of the atmosphere into space. Because unfixed hydrogen has a low molecular weight, it can achieve escape velocity more readily and it leaks into outer space at a greater rate than other gasses. The leakage of hydrogen into space contributes to the pushing of the Earth from an initially reducing state to its current oxidizing one.

Photosynthesis provided a source of free oxygen, but the loss of reducing agents such as hydrogen is believed to have been a necessary precondition for the widespread accumulation of oxygen in the atmosphere. Hence the ability of hydrogen to escape from the Earth's atmosphere may have influenced the nature of life that developed on the planet. In the current, oxygen-rich atmosphere most hydrogen is converted into water before it has an opportunity to escape. Instead, most of the hydrogen loss comes from the destruction of methane in the upper atmosphere.

The Earth's magnetic field, according to dynamo theory, is generated within the molten outer core region where heat creates convection motions of conducting materials, generating electric currents. These in turn produce the Earth's magnetic field.

Earth orbits the Sun at an average distance of about 150 million kilometres every 365.2564 mean solar days, or one sidereal year. From Earth, this gives an apparent movement of the Sun eastward with respect to the stars. Because of this motion, on average it takes 24 hours a solar day for Earth to complete a full rotation about its axis so that the Sun returns to the meridian. The orbital speed of the Earth averages about 29.8 km/s (107,000 km/h), which is fast enough to cover the distance to the Moon (384,000 km) in four hours.

The Moon revolves with the Earth around a common barycentre every 27.32 days relative to the background stars. Viewed from the celestial North Pole, the motion of Earth, the Moon and their axial rotations are all counter-clockwise. Viewed from a vantage point above the north poles of both the Sun and the Earth, the Earth appears to revolve in a counter clockwise direction about the Sun. Earth's axis is tilted some 23.4 degrees from the perpendicular to the Earth Sun plane, and the Earth Moon plane is tilted about 5 degrees against the Earth-Sun plane. Without this tilt, there would be an eclipse every two weeks, alternating between lunar eclipses and solar eclipses.

The Hill sphere, or gravitational sphere of influence, of the Earth is about 1.5 Gm (or 1,500,000 kilometres) in radius. This is maximum distance at which the Earth's gravitational influence is stronger than the more distant Sun and planets. Objects must orbit the Earth within this radius, or they can become unbound by the gravitational perturbation of the Sun.

The Solar System is situated in the Milky Way galaxy, orbiting about 28,000 light years from the centre of the galaxy. It is currently about 20 light years above the galaxy's equatorial plane in the Orion spiral arm.

Because of the axial tilt of the Earth, the amount of sunlight reaching any given point on the surface varies over the course of the year. This results in seasonal change in climate, with summer in the northern hemisphere occurring when the North Pole is pointing toward the Sun, and winter taking place when the pole is pointed away. During the summer, the day lasts longer and the Sun climbs higher in the sky. In winter, the climate becomes generally cooler and the days shorter. Above the Arctic Circle, an extreme case is reached where there is no daylight at all for part of the year a polar night. In the southern hemisphere the situation is exactly reversed, with the South Pole oriented opposite the direction of the North Pole.

In the northern hemisphere, Winter Solstice occurs on about December 21, Summer Solstice is near June 21, Spring Equinox is around March 20 and Autumnal Equinox is about September 23. In the Southern hemisphere, the situation is reversed, with the Summer and Winter Solstices exchanged and the Spring and Autumnal Equinox dates switched.

Earth has at least five co-orbital asteroids. As of 2011, there are 931 operational, man-made satellites orbiting the Earth.

A planet that can sustain life is termed habitable, even if life did not originate there. The Earth provides the (currently understood) requisite conditions of liquid water, an environment where complex organic molecules can assemble, and sufficient energy to sustain metabolism. The distance of the Earth from the Sun, as well as its orbital eccentricity, rate of rotation, axial tilt, geological history, sustaining atmosphere and protective magnetic field all contribute to the conditions believed necessary to originate and sustain life on this planet.

The planet's life forms are sometimes said to form a "biosphere". This biosphere is generally believed to have begun evolving about 3.5 billion years ago. Earth is the only place where life is known to exist.

The Earth provides resources that are exploitable by humans for useful purposes. Some of these are non-renewable resources, such as mineral fuels, that are difficult to replenish on a short time scale.

Large deposits of fossil fuels are obtained from the Earth's crust, consisting of coal, petroleum, natural gas and methane clathrate. These deposits are used by humans both for energy production and as feedstock for chemical production.

The estimated amount of irrigated land in 1993 was 2,481,250 km².

Large areas of the Earth's surface are subject to extreme weather such as tropical cyclones, hurricanes, or typhoons that dominate life in those areas. Many places are subject to earthquakes, landslides, tsunamis, volcanic eruptions, tornadoes, sinkholes, blizzards, floods, droughts, and other calamities and disasters.

Many localized areas are subject to human-made pollution of the air and water, acid rain and toxic substances, loss of vegetation (overgrazing, deforestation, desertification), loss of wildlife, species extinction, soil degradation, soil depletion, erosion, and introduction of invasive species.

According to the United Nations, a scientific consensus exists linking human activities to global warming due to industrial carbon dioxide emissions. This is predicted to produce changes such as the melting of glaciers and ice sheets, more extreme temperature ranges, significant changes in weather and a global rise in average sea levels.

Earth has approximately 7,000,000,000 human inhabitants as of April 25, 2011. Projections indicate that the world's human population will reach 9.2 billion in 2050. Most of the growth is expected to take place in developing nations. Human population density varies widely around the world, but a majority live in Asia. By 2020, 60% of the world's population is expected to be living in urban, rather than rural, areas.

It is estimated that only one-eighth of the surface of the Earth is suitable for humans to live as three-quarters is covered by oceans, and half of the land area is either desert (14%), high mountains (27%), or other less suitable terrain.

As of 2011 there are 203 sovereign states, including the 192 United Nations member states. In addition, there are 59 dependent territories, and a number of autonomous areas, territories under dispute and other entities. Historically, Earth has never had a sovereign government with authority over the entire globe, although a number of nation-states have striven for world domination and failed.

The United Nations is a worldwide intergovernmental organization that was created with the goal of intervening in the disputes between nations, thereby avoiding armed conflict. It is not, however, a world government. The U.N. serves primarily as a forum for international diplomacy and international law. When the consensus of the membership permits, it provides a mechanism for armed intervention.

The first human to orbit the Earth was Yuri Gagarin on April 12, 1961. In total, about 400 people visited outer space and reached Earth orbit as of 2004, and, of these, twelve have walked on the Moon. Normally the only humans in space are those on the International Space Station. The station's crew, currently six people, is usually replaced every six months. The furthest humans have travelled from Earth is 400,171 km, achieved during the 1970 Apollo 13 mission.

Unlike the rest of the planets 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. In many cultures the mother goddess is also portrayed as a fertility deity. Creation myths in many religions recall a story involving the creation of the Earth by a supernatural deity or deities. A variety of religious groups, often associated with fundamentalist branches of Protestantism or Islam, assert that their interpretations of these creation myths in sacred texts are literal truth and should be considered alongside or replace conventional scientific accounts of the formation of the Earth and the origin and development of life. Such assertions are opposed by the scientific community and by other religious groups. A prominent example is the creation-evolution controversy.

In the past there were varying levels of belief in a flat Earth, But this was displaced by the concept of a spherical Earth due to observation and circumnavigation. The human perspective regarding the Earth has changed following the advent of spaceflight, and the biosphere is now widely viewed from a globally integrated perspective. This is reflected in a growing environmental movement that is concerned about humankind's effects on the planet.

The future of the planet is closely tied to that of the Sun. As a result of the steady accumulation of helium at the Sun's core, the star's total luminosity will slowly increase. The luminosity of the Sun will grow by 10% over the next 1.1 billion years and by 40% over the next 3.5 Billion Years. Climate models indicate that the rise in radiation reaching the Earth is likely to have dire consequences, including the loss of the planet's oceans.

The Earth's increasing surface temperature will accelerate the inorganic CO2 cycle, reducing its concentration to levels lethally low for plants (10 ppm for C4 photosynthesis) in approximately 500 million to 900 million years. The lack of vegetation will result in the loss of oxygen in the atmosphere, so animal life will become extinct within several million more years. After another billion years all surface water will have disappeared and the mean global temperature will reach 70 °C. The Earth is expected to be effectively habitable for about another 500 million years from that point, although this may be extended up to 2.3 billion years if the nitrogen is removed from the atmosphere. Even if the Sun were eternal and stable, the continued internal cooling of the Earth would result in a loss of much of its CO2 due to reduced volcanism, and 35% of the water in the oceans would descend to the mantle due to reduced steam venting from mid-ocean ridges.

The Sun, as part of its evolution, will become a red giant in about 5 Gyr. Models predict that the Sun will expand out to about 250 times its present radius, roughly 1 AU (150,000,000 km). Earth's fate is less clear. As a red giant, the Sun will lose roughly 30% of its mass, so, without tidal effects, the Earth will move to an orbit 1.7 AU (250,000,000 km) from the Sun when the star reaches it maximum radius. The planet was therefore initially expected to escape envelopment by the expanded Sun's sparse outer atmosphere, though most, if not all, remaining life would have been destroyed by the Sun's increased luminosity peaking at about 5000 times its present level. However, a 2008 simulation indicates that Earth's orbit will decay due to tidal effects and drag, causing it to enter the red giant Sun's atmosphere and be vaporized.