WHAT IS EARTH SCIENCE?
Earth Science is a term for the sciences related to the planet Earth.
Earth is actually composed of three major parts or layers: the solid earth (which includes the parts near or at the surface, the asthenosphere and lithosphere), the atmosphere (the blanket of air that envelopes the earth), and the hydrosphere (the water parts, including ocean, streams and air moisture). These parts are not as distinct as this suggests, but interact continually to form, destroy and recycle the elements that make up all of life.
SCIENCES OF THE EARTH'S SPHERES
Geology covers the rocky parts of the Earth (the lithosphere) including the planet's core, mantle, and crust. Major disciplines are paleontology, minerology, sedimentology, and geophysics.
Oceanography describes the marine and freshwater domains of the watery parts of the Earth (the hydrosphere). Disciplines include hydrogeology, chemical and biological oceanography.
Atmospheric Sciences cover the gaseous parts of the Earth (the atmosphere).
Glaciology covers the icy parts of the Earth (the cryosphere).
THE SOLID EARTH AND ITS STRUCTURE
The earth is made up of several layers or spheres, the thickest being its inner core, the outer core, and the mantle. The thinnest layer, which is only 5-40 kilometres thick, is the crust, which contains all of the land and water forms, and life forms, with which we are familiar.
These layers are the result of processes that formed the solar system and Earth, and are believed to be still occurring, though on a much smaller scale.
In 1915, a German geo-physicist, Alfred Wegener, argued that the present day continents were originally one continent that he called Pangaea (which means “all land”), and that around 200 million years ago, it began to break into smaller continents that gradually drifted into their present positions.
The evidence that Wegener gave for this hypothesis was that the South American and African continents fit together like pieces of a jigsaw. Also, fossils that should have only been found in certain geographical zones were found in other zones, like the fossil fern found throughout Africa, Australia, India and South America although the fern had grown only in a subpolar climate. Similarly, areas of rocks of the same type and age found on one continent have been perfectly matched to rock areas on other continents.
Minerals combine or interact to form all rocks. Rocks are classified according to how they were formed: igneous (fire), metamorphic (changed form), or sedimentary (deposition of sediments). Within each class of rocks, different rocks are identified according to their mineral composition.
Igneous rocks are formed when molten rock, magma, cools and crystallises to the solid state. This class of rocks includes granite, basalt, obsidian, pumice and rhyolite. Igneous rocks can be identified by their composition and texture. Their mineral composition reflects the chemical composition of the original magma.
These are the most common and widely found of the three rock classes. They are formed from sediments that have been compressed and sometimes chemically affected to form rock. Because of the method of their formation, they often contain features, such as fossils, that tell us about the origin and history.
Metamorphic rocks are really recycled rocks. As parts of the earth’s crust are subducted in plate tectonics activity, the rocks are subjected to enormous pressure and heat that transform (metamorphose) them. Metamorphic rocks are formed at depths in the earth’s crust, most commonly in mountain regions.
The oceans cover seven-tenths (7/10) of our planet, giving it the appearance of a blue jewel from very far away. Yet we know far less about our oceans than we do about our land areas. Sustained study of our oceans began only in the 1960’s, and it was only in the 1980’s that oceanographers discovered that the deep ocean floor is not calm, but experiences violent underwater storms.
Although we speak of several oceans and seas, oceans are not bounded, except on our maps. Their water is continually circulating around the globe, reforming into clouds, then into high mountain streams, to end up back in the ocean, probably somewhere else. Driven by the sun’s energy, the wind, and the earth’s rotation, powerful surface currents carry great rivers of ocean water between the poles and the tropics. The Gulf Stream rising in the Gulf of Mexico moves up the east coast of North America, and across the Atlantic to Northern Europe. The Kuroshio current carries warm water from the Philippines to Japan, Hawaii, and the American west coast.
The atmosphere is hundreds of kilometres thick, and while it is largely invisible to the naked eye, except for clouds and precipitation activity (rain, hail, snow), it is very important. The atmosphere provides the air that we breathe, allows for the circulation of gases, such as carbon dioxide and oxygen between life forms, and protects the planet from the intense radiation and heat of the sun. All of our weather and climate are caused by the exchanges of energy that continually occur between the atmosphere and the surface of the earth, and between the atmosphere and space.
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