Question

Earth

The Blue Marble photograph of Earth, taken during the Apollo 17 lunar mission in 1972
Orbital characteristics
Epoch J2000
Aphelion	152,100,000 km (94,500,000 mi) (7011152100643076810â™ 1.01673 AU) 
Perihelion	147,095,000 km (91,401,000 mi) (7011147094903845957â™ 0.9832687 AU) 
Semi-major axis	149,598,023 km (92,955,902 mi) (7011149598022990632â™ 1.000001018 AU) 
Eccentricity	6998167086000000000â™ 0.0167086
Orbital period	7007315581497635456â™ 365.256363004 d  (7000100001742095999â™ 1.00001742096 yr)
Average orbital speed	29.78 km/s (18.50 mi/s) (107,200 km/h (66,600 mph))
Mean anomaly	7002358617000000000♠358.617°
Inclination	7000715500000000000♠7.155° to the Sun's equator; 1.57869° to invariable plane; 0.00005° to J2000 ecliptic
Longitude of ascending node	2998887393600000000♠−11.26064° to J2000 ecliptic
Argument of perihelion	7002114207830000000â™ 114.20783°
Satellites	1 natural satellite: the Moon 5 quasi-satellites >1,400 operational artificial satellites >16,000 space debris
Physical characteristics
Mean radius	6,371.0 km (3,958.8 mi)
Equatorial radius	6,378.1 km (3,963.2 mi)
Polar radius	6,356.8 km (3,949.9 mi)
Flattening	6997335280000000000â™ 0.0033528 1/298.257222101 (ETRS89)
Circumference	40,075.017 km (24,901.461 mi) (equatorial)  40,007.86 km (24,859.73 mi) (meridional) 
Surface area	510,072,000 km2 (196,940,000 sq mi)  148,940,000 km2 (57,510,000 sq mi) (29.2%) land  361,132,000 km2 (139,434,000 sq mi) (70.8%) water
Volume	7021108320999999999â™ 1.08321×1012 km3 (7011259876000000000â™ 2.59876×1011 cu mi)
Mass	7024597237000000000â™ 5.97237×1024 kg (7024597236001731600â™ 1.31668×1025 lb) (7024596565000000000â™ 3.0×10−6 M☉)
Mean density	5.514 g/cm3 (0.1992 lb/cu in)
Surface gravity	9.807 m/s2 (32.18 ft/s2) (7000100000000000000â™ 1 g)
Moment of inertia factor	0.3307
Escape velocity	11.186 km/s (6.951 mi/s)
Sidereal rotation period	7004861641003520000â™ 0.99726968 d (23h 56m 4.100s)
Equatorial rotation velocity	1,674.4 km/h (1,040.4 mph)
Axial tilt	23.4392811°
Albedo	0.367 geometric 0.306 Bond
Surface temp. min mean max Kelvin 184 K 288 K 330 K Celsius −89.2 Â°C 15 Â°C 56.7 Â°C Fahrenheit −128.5 Â°F 59 Â°F 134 Â°F
Atmosphere
Surface pressure	7005101325000000000â™ 101.325 kPa (at MSL)
Composition by volume	78.08% nitrogen (N2)(dry air) 20.95% oxygen (O2) 0.930% argon 0.0402% carbon dioxide ~ 1% water vapor (climate-variable)

Earth, otherwise known as the world, (Greek: Γαῖα Gaia; Latin: Terra) is the third planet from the Sun and the only object in the Universe known to harbor life. It is the densest planet in the Solar System and the largest of the four terrestrial planets.

According to radiometric dating and other sources of evidence, Earth formed about 4.54 billion years ago.Earth's gravity interacts with other objects in space, especially the Sun and the Moon, Earth's only natural satellite. During one orbit around the Sun, Earth rotates about its axis over 365 times, thus an Earth year is about 365.26 days long. Earth's axis of rotation is tilted, producing seasonal variations on the planet's surface. The gravitational interaction between the Earth and Moon causes ocean tides, stabilizes the Earth's orientation on its axis, and gradually slows its rotation.

Earth's lithosphere is divided into several rigid tectonic plates that migrate across the surface over periods of many millions of years. About 71% of Earth's surface is covered with water, mostly by its oceans. The remaining 29% is land consisting of continents and islands that together have many lakes, rivers and other sources of water that contribute to the hydrosphere. The majority of Earth's polar regions are covered in ice, including the Antarctic ice sheet and the sea ice of the Arctic ice pack. Earth's interior remains active with a solid iron inner core, a liquid outer core that generates the Earth's magnetic field, and a convecting mantle that drives plate tectonics.

Chemical composition of the crust

Compound	Formula	Composition
		Continental	Oceanic
silica	SiO2	60.2%	48.6%
alumina	Al2O3	15.2%	16.5%
lime	CaO	5.5%	12.3%
magnesia	MgO	3.1%	6.8%
iron(II) oxide	FeO	3.8%	6.2%
sodium oxide	Na2O	3.0%	2.6%
potassium oxide	K2O	2.8%	0.4%
iron(III) oxide	Fe2O3	2.5%	2.3%
water	H2O	1.4%	1.1%
carbon dioxide	CO2	1.2%	1.4%
titanium dioxide	TiO2	0.7%	1.4%
phosphorus pentoxide	P2O5	0.2%	0.3%
Total		99.6%	99.9%

Geologic layers of Earth

Earth cutaway from core to exosphere. Not to scale.	Depth km	Component layer	Density g/cm3
	0–60	Lithosphere	—
	0–35	Crust	2.2–2.9
	35–60	Upper mantle	3.4–4.4
	35–2890	Mantle	3.4–5.6
	100–700	Asthenosphere	—
	2890–5100	Outer core	9.9–12.2
	5100–6378	Inner core	12.8–13.1

Present-day major heat-producing isotopes

Isotope	Heat release W/kg isotope	Half-life years	Mean mantle concentration kg isotope/kg mantle	Heat release W/kg mantle
238U	94.6 × 10−6	4.47 × 109	30.8 × 10−9	2.91 × 10−12
235U	569 × 10−6	0.704 × 109	0.22 × 10−9	0.125 × 10−12
232Th	26.4 × 10−6	14.0 × 109	124 × 10−9	3.27 × 10−12
40K	29.2 × 10−6	1.25 × 109	36.9 × 10−9	1.08 × 10−12

Earth's major plates

Plate name	Area 106 km2
Pacific Plate	103.3
African Plate	78.0
North American Plate	75.9
Eurasian Plate	67.8
Antarctic Plate	60.9
Indo-Australian Plate	47.2
South American Plate	43.6

Estimated human land use, 2000

Land use	Mha
Cropland	1,510–1,611
Pastures	2,500–3,410
Natural forests	3,143–3,871
Planted forests	126–215
Urban areas	66–351
Unused, productive land	356–445

Characteristics

Diameter	3,474.8 km
Mass	7.349×1022 kg
Semi-major axis	384,400 km
Orbital period	27 d 7 h 43.7 m

• 7000715500000000000â™ 7.155° to the Sun's equator;
• 1.57869° to invariable plane;
• 0.00005° to J2000 ecliptic

• 1 natural satellite: the Moon
• 5 quasi-satellites
• >1,400 operational artificial satellites
• >16,000 space debris

• 40,075.017 km (24,901.461 mi) (equatorial) 
• 40,007.86 km (24,859.73 mi) (meridional) 

• 510,072,000 km² (196,940,000 sq mi)
•  148,940,000 km² (57,510,000 sq mi) (29.2%) land
•  361,132,000 km² (139,434,000 sq mi) (70.8%) water

• 0.367 geometric
• 0.306 Bond

• 78.08% nitrogen (N₂)(dry air)
• 20.95% oxygen (O₂)
• 0.930% argon
• 0.0402% carbon dioxide
• ~ 1% water vapor (climate-variable)

• Proximity to oceans moderates the climate. For example, the Scandinavian peninsula has more moderate climate than similarly northern latitudes of northern Canada.
• The wind enables this moderating effect. The windward side of a land mass experiences more moderation than the leeward side. In the Northern Hemisphere, the prevailing wind is west-to-east, and western coasts tend to be milder than eastern coasts. This is seen in Eastern North America and Western Europe, where rough continental climates appear on the east coast on parallels with mild climates on the other side of the ocean. In the Southern Hemisphere, the prevailing wind is east-to-west, and the eastern coasts are milder.
• The distance from the Earth to the Sun varies. The Earth is closest to the Sun (at perihelion) in January, which is summer in the Southern Hemisphere. It is furthest away (at aphelion) in July, which is summer in the Northern Hemisphere, and only 93.55% of the solar radiation from the Sun falls on a given square area of land than at perihelion. Despite this, there are larger land masses in the Northern Hemisphere, which are easier to heat than the seas. Consequently, summers are 2.3 Â°C (4 Â°F) warmer in the Northern Hemisphere than in the Southern Hemisphere under similar conditions.
• The climate is colder at high altitudes than at sea level because of the decreased air density.

•   North America
•   South America
•   Antarctica

•   Europe
•   Africa

•   Asia
•   Oceania

• Celestial sphere
• Earth physical characteristics tables
• Earth science
• Earth system science
• Timeline of the far future

• Comins, Neil F. (2001). Discovering the Essential Universe (2nd ed.). New York: W. H. Freeman. Bibcode:2003deu..book.....C. ISBN . OCLC 52082611. 

• National Geographic encyclopedic entry about Earth
• Earth â€“ Profile â€“ Solar System Exploration – NASA
• Earth â€“ Climate Changes Cause Shape to Change – NASA
• United States Geological Survey – USGS
• Earth â€“ Astronaut Photography Gateway – NASA
• Earth Observatory – NASA
• Earth â€“ Audio (29:28) â€“ Cain/Gay â€“ Astronomy Cast (2007)
• Earth â€“ Videos â€“ International Space Station:
  • Video (01:02) â€“ Earth (time-lapse)
  • Video (00:27) â€“ Earth and Auroras (time-lapse)

• Video (01:02) â€“ Earth (time-lapse)
• Video (00:27) â€“ Earth and Auroras (time-lapse)

...
Wikipedia