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Geography
: Mineral Resources, Energy Resources, Why I hated Geography at school, Universe, Structure of the Earth, Earth Layers, Earth Composition, Tectonics, Human Geography, Geomorphology, Oceanography, Cartography, History, Landforms, Climatology, Soils, Vegetation, Regions, Population, Resources, Industries |
| Landforms:
Earth Contraction & Expansion, Fluvial Plains, Fold Mountains, Geosynclines: Evolution, Geosynclines, Glaciated & Depositional Plains, Himalayas, Jura & Appalachian Mountains, Mountain building, Mountain types, Mountains, Plains, Plate Tectonics, Economic Importance of Plateaus, Plateaus, Rocky Mountains & Alps |
1. Welcome, lone traveler from Ashburn!
Earth Contraction & Expansion
Many hypothesis have been proposed in connection with the building of Fold Mountains because scholars have great differences over the mountain building processes. The hypothesis related to the origin of continents and the oceans have already been discussed. Those hypothesis bearing upon the mountain building process have been discussed briefly.
Hypothesis Related to Contraction of Earth
The basis of these hypothesis is the cooling of the earth from its early red-hot condition to the present cooled condition. During the cooling, the earth contracted. Those who contributed to these hypothesis are Lapworth and Love, Gregory, Sues and Argand, Chamberlain, Kober Jeffreys, etc.
2. Main article
All these scholars have supposed that the earth in its initial condition was very hot. Due to slow cooling, its upper layers cooled faster than the inner ones. The contractions caused in cooling the upper layer gave birth to folds. All of the workers have accepted the existence of forelands (stable blocks) and the mobile areas (geosynclines). Due to contraction, the compressive forces raised the sediment of the geosyncline into folded mountains.
Sues and Argand recognize four forelands:
3. References
(i) Laurentia
(ii) Baltic Shield
(iii) Angaraland
(iv) Gondwanaland
Scholars believe that the mountains are not formed in one step. Many mountain building periods occur. Jeffreys explained this fact in this hypothesis. He also discussed the periods of quiescence (Quiet period) and orogenetic upheaval (Mountain building movement).
Hypothesis Related to Expansion of Earth
A new hypothesis has been proposed more recently. Longwell and Flint have briefly described this hypothesis. The hypothesis of the expanding of the earth is no less interesting than that of contraction. Scholars believe in the expansion of many stars. Hence, many scholars believe that the earth is expanding. Many fissures were formed on account of expansion and looked like trenches on sea floors. These trenches are found scattered in the Pacific and the Indian oceans. This proves that Africa had separated from Europe later on. Due to the expansion continuing from Mesozoic era to the present, the Atlantic Ocean was formed. The contraction of the crust is considered to be the cause of mountain building but those who believe in the expansion of the Earth think that mountains were formed due to the distortion caused by the melting and flow of ice sheets. No doubt it is very difficult to say whether the earth is expanding or contracting, yet the new hypothesis cannot be said to be entirely baseless.
Next: Fluvial Plains |
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