Earth

بسم الله الرحمن الرحيم

"Reciting Salawath on our Prophet Muhammad (peace be upon him) is an activity that will be accepted by Allah, even if we don't have Ikhlas (piety)".

Earth (pronounced /ˈɜrθ/) is the third planet from the Sun and is the largest of the terrestrial planets in the Solar System, in both diameter and mass. It is also referred to as the Earth, Planet Earth, Gaia, Terra, and "the World".

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, both in terms of size and mass. Of these four planets, Earth also has the highest density, the highest surface gravity and the strongest magnetic field.

Home to millions of species including humans, Earth is the only place in the universe where life is known to exist. Scientific evidence indicates that the planet formed 4.54 billion years ago, and life appeared on its surface within a billion years. Since then, 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 radiation, permitting life on land.

Earth's outer surface is divided into several rigid segments, or tectonic plates, that gradually 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; liquid water, necessary for all known life, is not known to exist on any other planet's surface. Earth'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 outer space, including the Sun and the Moon. At present, Earth orbits the Sun once for every roughly 366.26 times it rotates about its axis. This length of time is a sidereal year, which is equal to 365.26 solar days. Earth's axis of rotation is tilted 23.4° away from the perpendicular to 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. A cometary bombardment during the early history of the planet played a role in the formation of the oceans. Later, asteroid impacts caused significant changes to the surface environment. Long term periodic changes in the Earth's orbit, caused by the gravitational influence of other planets, are believed to have given rise to the ice ages that have intermittently covered significant portions of Earth's surface in glacial sheets.

Scientists have been able to reconstruct detailed information about the planet's past. Earth and the other planets in the Solar System formed 4.54 billion years ago 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 soon afterwards, possibly as the result of a Mars-sized object (sometimes called Theia) with about 10% of the Earth's mass impacting the Earth in a glancing blow. 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 form the Moon.

Outgassing and volcanic activity produced the primordial atmosphere. Condensing water vapor, augmented by ice delivered by comets, produced the oceans. The highly energetic chemistry is believed to have produced a self-replicating molecule around 4 billion years ago, and half a billion years later, the last common ancestor of all life existed.

The development of photosynthesis allowed the Sun's energy to be harvested directly by life forms; the resultant oxygen accumulated in the atmosphere and resulted in a layer of ozone (a form of molecular oxygen [O3]) in the upper atmosphere. The incorporation of smaller cells within larger ones resulted in the development of complex cells called eukaryotes. True multicellular organisms formed as cells within colonies became increasingly specialized. Aided by the absorption of harmful ultraviolet radiation by the ozone layer, life colonized the surface of Earth.

As the surface continually reshaped itself, over hundreds of millions of years, continents formed and broke up. The continents migrated across the surface, occasionally combining to form a supercontinent. Roughly 750 million years ago (mya), the earliest known supercontinent, Rodinia, began to break apart. The continents later recombined to form Pannotia, 600–540 mya, then finally Pangaea, which broke apart 180 mya.

Since the 1960s, it has been hypothesized that severe glacial action between 750 and 580 mya, during the Neoproterozoic, covered much of the planet in a sheet of ice. This hypothesis has been termed "Snowball Earth", and is of particular interest because it preceded the Cambrian explosion, when multicellular life forms began to proliferate.

Following the Cambrian explosion, about 535 mya, there have been five mass extinctions. The last extinction event occurred 65 mya, when a meteorite collision probably triggered the extinction of the (non-avian) dinosaurs and other large reptiles, but spared small animals such as mammals, which then resembled shrews. Over the past 65 million years, mammalian life has diversified, and several mya, an African ape-like animal gained the ability to stand upright. This enabled tool use and encouraged communication that provided the nutrition and stimulation needed for a larger brain. The development of agriculture, and then civilization, allowed humans to influence the Earth in a short time span as no other life form had, affecting both the nature and quantity of other life forms.

The present pattern of ice ages began about 40 mya, then intensified during the Pleistocene about 3 mya. The Polar Regions have since undergone repeated cycles of glaciation and thaw, repeating every 40–100,000 years. The last ice age ended 10,000 years ago.

Orbital characteristics

Aphelion

152,097,701 km

1.0167103335 AU

Perihelion

147,098,074 km

0.9832898912 AU

Semi-major axis

149,597,887.5 km

1.0000001124 AU

Eccentricity

0.016710219

Orbital period

365.256366 days

1.0000175 yr

Avg. orbital speed

29.783 km/s

107,218 km/h

Inclination

7.25° to Sun's equator

Longitude of ascending node

348.73936°

Argument of perihelion

114.20783°

Satellites

1 (the Moon)

Physical characteristics

Mean radius

6,371.0 km

Equatorial radius

6,378.1 km

Polar radius

6,356.8 km

Flattening

0.0033528

Circumference

40,075.02 km (equatorial)

40,007.86 km (meridional)

40,041.47 km (mean)

Surface area

510,072,000 km²

148,940,000 km² land (29.2 %)

361,132,000 km² water (70.8 %)

Volume

1.0832073×1012 km³

Mass

5.9736×1024 kg

Mean density

5,515.3 kg/m³

Equatorial surface gravity

9.780327 m/s²

0.99732 g

Escape velocity

11.186 km/s

40,270 km/h

Sidereal rotation period

0.997258 d

23h 56m 04.09054s

Rotation velocity at equator

465.11 m/s

Axial tilt

23.439281°

Albedo

0.367

Surface temp.:

In Kelvin min 185 K mean 287 K & max 331 K

In Celsius min -88.3 °C mean 14 °C & max 57.7 °C

Adjectives

Terrestrial, Terran, Telluric, Tellurian, Earthly

Atmosphere

Surface pressure

101.3 kPa (MSL)

Composition

78.08% N2

20.95% O2

0.93% Argon

0.038% Carbon dioxide

Trace water vapor (varies with climate)