E A R T H
'C L A S I C A L' S U N M E R C U R Y V E N U S M O O N M A R S J U P I T E R S A T U R N
'A S T R O N O M I C A L' E A R T H U R A N U S N E P T U N E P L U T O
D W A R F P L A N E T S, M O O N S & A S T E R O I D S
'A S T R O N O M I C A L' E A R T H U R A N U S N E P T U N E P L U T O
D W A R F P L A N E T S, M O O N S & A S T E R O I D S
“It suddenly struck me that that tiny pea, pretty and blue, was the Earth. I put up my thumb and shut one eye, and my thumb blotted out the planet Earth. I didn't feel like a giant. I felt very, very small.”
NEIL ARMSTRONG
NEIL ARMSTRONG
What's to say about the Earth that David Attenborough hasn't already said.
Third planet from Sun, densest and fifth-largest of the eight planets in the Solar System, largest of the Solar System's four terrestrial planets, formed 4.54 billion years ago, life appeared on its surface within one billion years, home to millions of species, including humans... 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 physical properties of the Earth, as well as its geological history and orbit, have allowed life to persist during this period. 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 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 solid ice (Antarctic ice sheet) or sea ice (Arctic ice cap). 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. Right now, 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 center of the universe, and a modern perspective of the world as an integrated environment that requires stewardship. The planet is expected to continue supporting life for at least another 500 million years (unless its most evolved life-form decides to do something really dumb). |