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Earth
Table of Contents
Earth

 * Introduction & Top Questions
   
 * 
   Basic planetary data
   
 * The atmosphere and hydrosphere
    * The atmosphere
   
    * The hydrosphere

 * 
   The outer shell
   
 * 
   The interior
   
 * 
   The geomagnetic field and magnetosphere
   
 * Development of Earth’s structure and composition
    * Accretion of the early Earth
   
    * Effects of planetesimal impacts
   
    * Planetary differentiation

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Home Science Astronomy


EARTH

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By Raymond Jeanloz | See All • Edit History

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Table of Contents
Top Questions
WHAT IS EARTH?

Earth is the third planet from the Sun and the fifth largest planet in the solar
system in terms of size and mass. Its near-surface environments are the only
places in the universe known to harbour life.

WHERE IS EARTH IN THE MILKY WAY GALAXY?

Earth is located in the Orion-Cygnus Arm, one of the four spiral arms of the
Milky Way, which lies about two-thirds of the way from the centre of the Galaxy.

WHAT IS EARTH NAMED FOR?

Earth’s name in English, the international language of astronomy, derives from
Old English and Germanic words for ground and earth, and it is the only name for
a planet of the solar system that does not come from Greco-Roman mythology.

WHAT WAS EARTH LIKE WHEN IT WAS FIRST FORMED?

Earth and the other planets in the solar system formed about 4.6 billion years
ago. The early Earth had no ozone layer and no free oxygen, lacked oceans, and
was very hot.

WHAT DOES EARTH LOOK LIKE?

Viewed from another planet, Earth would appear bright and bluish in colour. In
latitudinal belts, swirling white cloud patterns of midlatitude and tropical
storms can be seen. The polar regions would appear white because of ice, the
oceans a dark blue-black, the deserts a tawny beige, and forests and jungles a
vibrant green.



Earth, third planet from the Sun and the fifth largest planet in the solar
system in terms of size and mass. Its single most outstanding feature is that
its near-surface environments are the only places in the universe known to
harbour life. It is designated by the symbol ♁. Earth’s name in English, the
international language of astronomy, derives from Old English and Germanic words
for ground and earth, and it is the only name for a planet of the solar system
that does not come from Greco-Roman mythology.


Earth
A composite image of Earth captured by instruments aboard NASA's Suomi National
Polar-orbiting Partnership satellite, 2012.
NASA/NOAA/GSFC/Suomi NPP/VIIRS/Norman Kuring

Since the Copernican revolution of the 16th century, at which time the Polish
astronomer Nicolaus Copernicus proposed a Sun-centred model of the universe (see
heliocentric system), enlightened thinkers have regarded Earth as a planet like
the others of the solar system. Concurrent sea voyages provided practical proof
that Earth is a globe, just as Galileo’s use of his newly invented telescope in
the early 17th century soon showed various other planets to be globes as well.
It was only after the dawn of the space age, however, when photographs from
rockets and orbiting spacecraft first captured the dramatic curvature of Earth’s
horizon, that the conception of Earth as a roughly spherical planet rather than
as a flat entity was verified by direct human observation. Humans first
witnessed Earth as a complete orb floating in the inky blackness of space in
December 1968 when Apollo 8 carried astronauts around the Moon. Robotic space
probes on their way to destinations beyond Earth, such as the Galileo and the
Near Earth Asteroid Rendezvous (NEAR) spacecraft in the 1990s, also looked back
with their cameras to provide other unique portraits of the planet.



Viewed from another planet in the solar system, Earth would appear bright and
bluish in colour. Easiest to see through a large telescope would be its
atmospheric features, chiefly the swirling white cloud patterns of midlatitude
and tropical storms, ranged in roughly latitudinal belts around the planet. The
polar regions also would appear a brilliant white, because of the clouds above
and the snow and ice below. Beneath the changing patterns of clouds would appear
the much darker blue-black oceans, interrupted by occasional tawny patches of
desert lands. The green landscapes that harbour most human life would not be
easily seen from space. Not only do they constitute a modest fraction of the
land area, which itself is less than one-third of Earth’s surface, but they are
often obscured by clouds. Over the course of the seasons, some changes in the
storm patterns and cloud belts on Earth would be observed. Also prominent would
be the growth and recession of the winter snowcap across land areas of the
Northern Hemisphere.

Scientists have applied the full battery of modern instrumentation to studying
Earth in ways that have not yet been possible for the other planets; thus, much
more is known about its structure and composition. This detailed knowledge, in
turn, provides deeper insight into the mechanisms by which planets in general
cool down, by which their magnetic fields are generated, and by which the
separation of lighter elements from heavier ones as planets develop their
internal structure releases additional energy for geologic processes and alters
crustal compositions.

Earth’s surface is traditionally subdivided into seven continental masses:
Africa, Antarctica, Asia, Australia, Europe, North America, and South America.
These continents are surrounded by five major bodies of water: the Arctic,
Atlantic, Indian, Pacific, and Southern oceans. However, it is convenient to
consider separate parts of Earth in terms of concentric, roughly spherical
layers. Extending from the interior outward, these are the core, the mantle, the
crust (including the rocky surface), the hydrosphere (predominantly the oceans,
which fill in low places in the crust), the atmosphere (itself divided into
spherical zones such as the troposphere, where weather occurs, and the
stratosphere, where lies the ozone layer that shields Earth’s surface and its
organisms against the Sun’s ultraviolet rays), and the magnetosphere (an
enormous region in space where Earth’s magnetic field dominates the behaviour of
electrically charged particles coming from the Sun).

Knowledge about these divisions is summarized in this astronomically oriented
overview. The discussion complements other treatments oriented to the Earth
sciences and life sciences. Earth’s figure and dimensions are discussed in the
article geodesy. Its magnetic field is treated in the article geomagnetic field.
The early evolution of the solid Earth and its atmosphere and oceans is covered
in geologic history of Earth. The geologic and biological development of Earth,
including its surface features and the processes by which they are created and
modified, are discussed in geochronology, continental landform, and plate
tectonics. The behaviour of the atmosphere and of its tenuous, ionized outer
reaches is treated in atmosphere, while the water cycle and major hydrologic
features are described in hydrosphere, ocean, and river. The solid Earth as a
field of study is covered in geologic sciences, the methods and instruments
employed to investigate Earth’s surface and interior are discussed in Earth
exploration, and the history of the study of Earth from antiquity to modern
times is surveyed in Earth sciences. The global ecosystem of living organisms
and their life-supporting stratum are detailed in biosphere.



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External Websites
 * National Geographic Kids - Structure of the Earth!
 * CIA - The World Factbook - World

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 * Earth - Children's Encyclopedia (Ages 8-11)
 * Earth - Student Encyclopedia (Ages 11 and up)

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 * Table Of Contents
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Select Citation Style
MLA APA Chicago Manual of Style
Jeanloz, Raymond , Lunine, Jonathan I. and Chapman, Clark R.. "Earth".
Encyclopedia Britannica, 8 Jul. 2021, https://www.britannica.com/place/Earth.
Accessed 14 April 2022.
Copy Citation
External Websites
 * National Geographic Kids - Structure of the Earth!
 * CIA - The World Factbook - World

Britannica Websites
Articles from Britannica Encyclopedias for elementary and high school students.
 * Earth - Children's Encyclopedia (Ages 8-11)
 * Earth - Student Encyclopedia (Ages 11 and up)



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