This compilation will help you to understand the basic terms in Geography.
To understand the interior of the Earth
- Crust – The outermost layer, or shell, of the earth (or any other differentiated) planet. Earth’s crust is generally defined as the part of the Earth above the Mohorovivic discontinuity. It represents less than one per cent of Earth’s total.
- Mantle – The zone of earth’s interior between the base line of the crust (the Mohorovivic (Moho) discontinuity) and the core. The mantle has an average density of about 3.3g/cm3 and accounts for about 68 per cent of earth’s mass. The mantle lies between the crust and the core of the earth. The lower layers of mantle are floored by the Gutenberg discontinuity.
- Core – The central part of the earth below the depth of 2900 Km.
- Mohorovivic (Moho) Discontinuity – The first global seismic discontinuity below the surface of the Earth. It lies at a depth varying from about 5 to 10 km beneath the ocean floor to about 35 km beneath the continents, commonly referred to as the Moho.
- Vulcanicity – The movement of magma, both into earth’s crust (intrusion) and onto Earth’s surface.
- Magma – A mobile silicate melt, which can contain suspended crystals and dissolved gasses as well as liquid.
- Silicate (silicate minerals) – A mineral containing silicon oxygen tetrahedral, in which four oxygen atoms surround each silicon.
- Seismology – It is the science which study various aspect of seismic waves, generated during the occurrence earthquakes.
- Seismic waves – The different types of tremors and waves generated during the occurrence of an earth quake are called seismic waves.
- Seismograph – Seismic waves are recorded with the help of an instrument known as seismograph.
- Sial – A general term for the silica – rich rocks that form the continental masses.
- Sima – A general term for the magnesium – rich igneous rocks (basalt, gabbro and peridotite) of the ocean basin.
- Nife – It is located just below ‘sima’ layer.this layer is composed of nickel (NI) and ferrium (Fe).
- Lithosphere –It is having thickness of about 100 km is mostly composed of granites. Silica and aluminium are dominant constituents. Average density is 3.5.
- Pyrosphere – It stretches for a thickness of 2780 km having an average density of 5.6. The dominant rock is Basalt.
To understand the continents and ocean basins
- Continent – A large landmass, from 20 to 60 km thick, composed mostly of granitic rock. Continents rise abruptly above the deep – ocean floor and include the marginal areas submerged beneath sea level. Examples – the African continent, the Asiatic continent, the North American and South American continent, etc.
- Basin – A depression into which the surrounding area drains.
- Plate- The rigid lithospheric slabs or rigid and solid crustal layers are tectonically called plates.
- Plate tectonics – The whole mechanism of the evolution, nature and motion of plates and resultant reaction.
- Constructive plate margins– these are also called as ‘divergent plate margins’ or ‘accreting plate margins’. Constructive plate margins (boundaries) represents zones of divergence where her is continues upwelling of molten materials (lava) and new oceanic crust is continuously formed.
- Destructive Plate margins – these are also called as ‘consuming plate margins’ or ‘convergent plate margin’ because two plates move towards each other or two plates converge along a line and leading edge of one plate overrides the other plate and the overridden pate is subducted or thrust into the mantle and thus part of the crust (plate) is lost in the mantle.
- Sea floor spreading – The theory of that the sea floor spreads laterally away from the oceanic ridge as new lithosphere is created along the crest of the ridge by igneous activity.
- Pangaea – About 700million years ago all the land masses were united together in the form of one single giant land mass known as Pangaea.
- Isostasy – The continental crust of earth has a visible part above the surface and lower, in visible one. The balance between these two is Isostasy. If part of the upper surface is removed by erosion, the continental crust will rise to offset this erosion, at least in part. Section of the continental crust have been pushed down by the weight of glacial ice, the extent of depression varying with the thickness of ice, and the density of the material below. It is believed that the critical size for an ice cap to depress a landmass is a 500km diameter. Landmass will rise again if the ice melts.