EARTH SCIENCE

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'Earth science' (also known as 'geoscience', 'the geosciences' or 'the Earth Sciences'), is an all-embracing term for the sciences related to the planet Earth. It is arguably a special case in planetary science, being the only known life-bearing planet. There are both reductionist and holistic approaches to Earth science. The major historic disciplines use physics, geology, geography, meteorology, mathematics, chemistry and biology to build a quantitative understanding of the principal areas or ''spheres'' of the Earth system.

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Earth's spheres

Earth's energy

Methodology

Partial list of the major Earth Science topics

Atmosphere

Biosphere

Hydrosphere

Lithosphere or geosphere

Earth's spheres

Earth science generally recognizes 4 spheres, the lithosphere, the hydrosphere, the atmosphere, and the biosphere. These correspond to rocks, water, air, and life. Some practitioners include the cryosphere (ice) as a distinct portion of the hydrosphere and the pedosphere (soil) as an active, intermixed sphere as part of Earth's spheres.

Lava flows from the Kīlauea volcano into the ocean on the Island of Hawaii

★ Geology describes the rocky parts of the Earth's crust (or lithosphere) and its historic development. Major subdisciplines are mineralogy and petrology, geochemistry, geomorphology, paleontology, stratigraphy, engineering geology and sedimentology.

★ Geophysics and Geodesy investigate the figure of the Earth, its reaction to forces and its magnetic and gravity fields. Geophysicists explore the Earth's core and mantle as well as the tectonic and seismic activity of the lithosphere.

★ Soil science covers the outermost layer of the Earth's crust that is subject to soil formation processes (or pedosphere). Major subdisciplines include edaphology and pedology.

★ Oceanography and hydrology (incl. limnology) describe the marine and freshwater domains of the watery parts of the Earth (or hydrosphere). Major subdisciplines include hydrogeology and physical, chemical, and biological oceanography.

★ Glaciology covers the icy parts of the Earth (or cryosphere).

★ Atmospheric sciences cover the gaseous parts of the Earth (or atmosphere) between the surface and the exosphere (~1000 km). Major subdisciplines are meteorology, climatology, atmospheric chemistry and atmospheric physics.

★ The most important and linking sphere is the biosphere, and consists of all forms of life, from single-celled organisms to pine trees to people. The interactions of Earth's other spheres - lithosphere/geosphere, hydrosphere, atmosphere and/or cryosphere and pedosphere - create the conditions that can support life.

Earth's energy

In geology, plate tectonics, mountain ranges, volcanoes, and earthquakes are phenomena that can be explained in terms of energy transformations in the Earth's crust^[1]. Recent studies suggest that the Earth transforms about 6.18 x 10^-12 J/s (joules per second) per kilogram. Given the Earth's mass, the rate of energy transformations inside the Earth is about 37 x 10¹² J/s (37 terawatts). The heat escaping from inside the Earth is only about 0.02% of the amount of energy Earth receives from Sun in the form of sunlight, and radiates back into space in the form of infrared blackbody radiation (~1.74 x 10¹⁷ J/s = 174 petawatts).
From the study of neutrinos radiated from the Earth (see KamLAND), scientists have recently estimated that about 24 terawatts (65%) of this rate of energy transformation is due to radioactive decay (principally of potassium 40, thorium 232 and uranium 238), and the remaining 13 terawatts is from the continuous gravitational ''sorting'' of the core and mantle of the earth, energies left over from the formation of the Earth, about 4.57 billion years ago (this sorting represents continuing gravitational collapse of the Earth into the maximally compact object which is consistent with its composition-- a process which releases gravitational potential energy), and finally - from tidal flexing of Earth's interior and crust. The magnitude of all of these energy sources decline over time, and based on half-life alone, it has been estimated that the current radioactive energy of the planet represents less than 1% of that which was available at the time the planet was formed.
As a result, geological forces of continental accretion, subduction and sea floor spreading, account for 90% of the Earth's energy. The remaining 10% of geological tectonic energy comes through hotspots produced by mantle plumes, resulting in shield volcanoes like Hawaii, geyser activity like Yellowstone or flood basalts like Iceland.
Tectonic process are driven by heat from the Earth's interior. The process is a simple heat engine which works via the upward buoyancy-induced motion of hot, low density magma after expansion by heat. The processes metamorphically alter crustal rocks, and (more importantly from the energy view) during orogenies, lift them up into mountain ranges. The potential energy represented by the mountain range's weight and height thus represents heat from the core of the Earth which has been partly transformed into gravitational potential energy. This potential energy may be suddenly released in landslides or tsunamis. Similarly, the energy release which drives an earthquake represents stresses in rocks that are mechanical potential energy which has been similarly stored from tectonic processes. An earthquake thus ultimately represents kinetic energy which is being released from elastic potential energy in rocks, which in turn has been stored from heat energy released by radioactive decay and gravitational collapse in the Earth's interior.
The energy which is responsible for the geological processes of erosion and deposition is a result of the interaction of solar energy and gravity. An estimated 23% of the total insolation is used to drive the water cycle. When water vapour condenses to fall as rain, it dissolves small amounts of carbon dioxide, making a weak acid. This acid acting upon the metallic silicate minerals that form most rocks produces chemical weathering, removing the metals, and leading to the production of rocks and sand, carried by wind and water downslope through gravity to be deposited at the edge of continents in the sea. Physical weathering of rocks is produced by the expansion of ice crystals, left by water in the joint planes of rocks. A geologic cycle is continued when these eroded sediments are buried and later uplifted into mountains.
Similarly meteorological phenomena like wind, rain, hail, snow, lightning, tornadoes and hurricanes, are all a result of energy transformations brought about by solar energy on the planet Earth. It has been estimated that the average total ''solar incoming radiation'' (or insolation) is about 1350 watts per square meter incident to the summit of the atmosphere, at the equator at midday, a figure known as the solar constant. Although this amount varies a little each year, as a result of solar flares, prominences and the sunspot cycle. Some 34% of this is immediately reflected by the planetary albedo, as a result of clouds, snowfields, and even reflected light from water, rock or vegetation. As more energy is received in the tropics than is re-radiated, while more energy is radiated at the poles than is received, climatic homeostasis is only maintained by a transfer of energy from the tropics to the poles.

This transfer of energy is what drives the winds and the ocean currents. Like biological processes, all meteorological processes involve transformation of energy from a concentrated form such as sunlight into a less concentrated form, such as far infrared radiation (i.e., heat radiation) at the much smaller characteristic temperatures that occur on Earth, and thus is diffused into many photons. However, energy may be temporarily locally stored during this process, and the sudden release of such stored sources is responsible for the dramatic processes mentioned above. For example, the kinetic energy of a snow-avalanche or hurricane is due to the sudden release of energy previously captured from solar radiations.

Methodology

Like all other scientists, Earth scientists apply the scientific method: formulate hypotheses after observation of and gathering data about natural phenomena and then test those hypotheses. In Earth science, data usually plays a major role in testing and formulating hypotheses.

Partial list of the major Earth Science topics

Pedosphere

★ Soil science

★
★ Edaphology

★
★ Pedology

Systems

★ Environmental science

★ Geography

★
★ Human geography

★
★ Physical Geography

★ Gaia theories

Others

★ Cartography

★ Geoinformatics (GIS)

★ Geostatistics

★ Geodesy and Surveying

Notes and references

1. http://okfirst.ocs.ou.edu/train/meteorology/EnergyBudget.html

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EARTH SCIENCE

Earth's spheres

Earth's energy

Methodology

Partial list of the major Earth Science topics

Atmosphere

Biosphere

Hydrosphere

Lithosphere or geosphere

Pedosphere

Systems

Others

Notes and references

See also

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