Earth science

Africa, Age of the earth, Air, Animal, Antarctica, Archaea, Arctic Ocean, Asia, Asthenosphere, Astronomy, Atlantic Ocean, Atmosphere, Atmospheric chemistry, Atmospheric physics, Atmospheric science, Atmospheric sciences, Bacteria, Biogeography, Biological organisation, Biology, Biome, Biosphere, Cartography, Chemical oceanography, Chemistry, Chronology, Climate, Climatology, Continent, Cosmic rays, Crust (geology), Cryosphere, Crystallography, Dynamo theory, Earth, Earth's atmosphere, Earth's core, Earth's crust, Earth's mantle, Earth (planet), Earth Day, Earth core, Earth sciences graphics software, Earthquake, Earthquakes, Ecology, Economic geology, Ecosystem, Edaphology, Electromagnet, Energy, Energy transformation, Engineering geology, Environmental geology, Environmental geoscience, Environmental science, Eukaryota, Europe, Evolution, Evolutionary history of life, Exosphere, Fauna, Fields of science, Figure of the Earth, Flora, Fungus, GIS, Gaia hypothesis, Gas, Gemology, Geoarchaeology, Geochemistry, Geochronology, Geodesy, Geodynamics, Geography, Geoinformatics, Geological history of Earth, Geology, Geology of solar terrestrial planets, Geomagnetic, Geomicrobiology, Geomorphology, Geophysics, Geostatistics, Glaciology, Glossary of geology terms, Goddard Space Flight Center, Gravimetry, Gravity field, Greenhouse effect, Hawaii (Island), Historical geology, History of the Earth, Holism, Houghton Mifflin, Human, Human geography, Hydrogeology, Hydrology, Hydrometeorology, Hydrosphere, Hypotheses, Ice, Indian Ocean, International Standard Book Number, Kīlauea, Life, Limnology, List of basic earth science topics, List of geoscience organizations, Lithosphere, Magma, Magnetic field, Magnetosphere, Marine biology, Marine geology, Mathematics, Matter, Mesosphere, Meteorology, Microorganism, Micropaleontology, Mineralogy, Mountain, Mutations, NASA Earth Science Enterprise, Natural environment, Natural science, Nature, Nitrogen, North America, Ocean, Oceania, Oceanography, Organism, Origin of life, Outline of earth science, Oxygen, Pacific Ocean, Paleoceanography, Paleoclimatology, Paleontology, Palynology, Pedology (soil study), Pedosphere, Petrology, Physical geography, Physical oceanography, Physics, Pine, Planetary geology, Planetary science, Plant, Plate tectonics, Prokaryote, Protist, Quaternary geology, Reductionist, Rock (geology), Science, Scientific method, Seafloor spreading, Sedimentology, Seismology, Soil, Soil science, Solar System, Solar wind, South America, Southern Ocean, Space, Speleology, Stratigraphy, Stratosphere, Structural geology, Structure of the Earth, Subduction, Surveying, Tectonics, Thermosphere, Time, Transform boundary, Troposphere, Uniformitarianism (science), Universe, Universities Space Research Association, Virus, Volcano, Volcanoes, Volcanology, Water, Weather, Wilderness, World,

Africa is the world's second-largest and second most-populous continent, after Asia. At about 30.2 million km² (11.7 million sq mi) including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area.^[2] With a billion people (as of 2009, see table) in 61 territories, it accounts for about 14.72% of the World's human population. The continent is surrounded by the Mediterranean Sea to the north, both the Suez Canal and the Red Sea along the Sinai Peninsula to the northeast, the Indian Ocean to the southeast, and the Atlantic Ocean to the west. Not counting the disputed territory of Western Sahara, there are 53 countries, including Madagascar and various island groups, associated with the continent.

Age of the earth

Modern geologists and geophysicists accept that the age of the Earth is around 4.54 billion years (4.54 × 10⁹ years ± 1%).^[1][2][3] This age has been determined by radiometric age dating of meteorite material and is consistent with the ages of the oldest-known terrestrial and lunar samples. The Sun, by comparison, is about 4.57 billion years old, about 30 million years older.

Air

The atmosphere of Earth is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention (greenhouse effect), and reducing temperature extremes between day and night. Dry air contains roughly (by volume) 78% nitrogen, 21% oxygen, 0.93% argon, 0.038% carbon dioxide, and small amounts of other gases. Air also contains a variable amount of water vapor, on average around 1%.

Animal

Animals are a major group of mostly multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously and independently. All animals are also heterotrophs, meaning they must ingest other organisms for sustenance.

Arctic Ocean

The Arctic Ocean, located in the Northern Hemisphere and mostly in the Arctic north polar region, is the smallest, and shallowest of the world's five major oceanic divisions.^[1] The International Hydrographic Organization (IHO) recognizes it as an ocean, although some oceanographers call it the Arctic Mediterranean Sea or simply the Arctic Sea, classifying it as one of the mediterranean seas of the Atlantic Ocean.^[2] Alternatively, the Arctic Ocean can be seen as the northernmost lobe of the all-encompassing World Ocean.

Asia

Asia is the world's largest and most populous continent, located in the eastern and northern hemispheres. It covers 8.6% of the earth's total surface area (or 29.9% of its land area) and with approximately 4 billion people, it hosts 60% of the world's current human population.

Asthenosphere

The asthenosphere (from Greek asthenēs 'weak' + sphere) is the mechanically weak ductily-deforming region of the upper mantle of the Earth. It lies below the lithosphere, at depths between 100 and 200 km (~ 62 and 124 miles) below the surface, but perhaps extending as deep as 400 km (~ 249 miles).

Astronomy

Astronomy is the scientific study of celestial objects (such as stars, planets, comets, nebulæ, star clusters and galaxies) and phenomena that originate outside the Earth's atmosphere (such as the cosmic background radiation). It is concerned with the evolution, physics, chemistry, meteorology, and motion of celestial objects, as well as the formation and development of the universe.

Atlantic Ocean

The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about 106.4 million square kilometres (41.1 million square miles), it covers approximately one-fifth of the Earth's surface and about one-quarter of its water surface area. The first part of its name refers to the Atlas of Greek mythology, making the Atlantic the "Sea of Atlas". The oldest known mention of this name is contained in The Histories of Herodotus around 450 BCE (I 202); see also: Atlas Mountains. Another name historically used was the ancient term Ethiopic Ocean, derived from Ethiopia, whose name was sometimes used as a synonym for all of Africa and thus for the ocean. Before Europeans discovered other oceans, the term "ocean" itself was to them synonymous with the waters beyond Western Europe that we now know as the Atlantic and which the Greeks had believed to be a gigantic river encircling the world; see Oceanus.

Atmosphere

An atmosphere (from Greek ἀτμός - atmos "vapor" and σφαῖρα - sphaira "sphere") is a layer of gases that may surround a material body of sufficient mass,^[1] by the gravity of the body, and are retained for a longer duration if gravity is high and the atmosphere's temperature is low. Some planets consist mainly of various gases, but only their outer layer is their atmosphere (see gas giants).

Atmospheric chemistry

Atmospheric chemistry is a branch of atmospheric science in which the chemistry of the Earth's atmosphere and that of other planets is studied. It is a multidisciplinary field of research and draws on environmental chemistry, physics, meteorology, computer modeling, oceanography, geology and volcanology and other disciplines. Research is increasingly connected with other areas of study such as climatology.