The Appalachian mountains orogeny dates back to the beginning of the Paleozoic era, about 530 million years ago. Today, these mountains are only a fragment of what used to be a much larger orogenic system, which had a direct northern continuation in the Caledonian mountain belt of Great Britain, east Greenland, and northwestern Scandinavia. This old mountain chain of North America extends some 3,200 km, from Newfoundland to Alabama, with an exposed width which ranges from 150 to 650 km. The narrowest part is in New York.
Orogenic Periods of the Appalachians
There are four major periods in the orogeny of the Appalachian mountain system.The Avalonian, which began in the Cambrian (520 million years ago); the Taconic, at the end of the Ordovician (445 million years ago); the Acadian, at the end of the Devonian (360 million years ago); and the Carboniferous-Permian (300 millions years). The first three orogenic periods can be seen in the northern Appalachians and Newfoundland, and the last orogenic period are exposed in the southern Appalachians and it is characterized by an intermontaine sag which was filled with intercontinental coal deposits. Therefore, the southern Appalachians consist of upper Paleozoic deposits, which are linked to important deposits of coal, gas, and oil, with its external wider zone comprising folds pointing northwest and accumulation of Lower and Middle Paleozoic granite and other rocks.
The last uplift and folding the southern Appalachians took place toward the end of the Paleozoic era. In the late Triassic period (Mesozoic era), however, the structure of the Appalachians was altered by grabens, which are elongated depressions of land between two faults. These grabens were then filled with red continental deposits and basalt extrusions. The western edge of the Appalachian mountain belt is a fold-and-thrust belt that impinges on the stable North American craton (a geologically stable portion of the continental crust that has not been deformed or altered significantly for millions of years). Along the western edge of the Appalachian mountains, sedimentary rocks span virtually the entire Paleozoic era, providing an extensive indirect record of nearby mountain building.
Geological Faults
Geological faults are breaks in the Earth’s crust. They can be caused by tension, compression or shearing forces, which the outermost layer of the planet constantly undergoes. Thus, there are three types of faults: normal fault, thrust fault, and strike/slip fault. Earthquake is associated by these geological features.
Normal fault
It is created when tension forces stretch the crust, which is constituted by either basalt or granite rocks. When the fault stretches to its breaking point, the rocks are moved along the direction of this force, causing an earthquake. A normal fault rips the crust at an angle; thus, a large piece of rock slides up as the other piece of geological material slides down, with the rocks that slides up becoming either mountains or plateau, while the rocks that slides down turning into rifts or river valleys. The Franklin Mountains of Texas, and Rio Grande rift is examples of this, respectively.
Thrust fault
Also called reverse fault, it is formed when compression forces smash the crust together. When the rock layer get ripped, it breaks at angle similar to a normal fault. This type of fault also creates mountains and rifts. Most mountains in Southern California are the consequences of thrust fault movements. The San Gabriel mountains, for example, are constantly being pushed up and over the rocks of the San Fernando and San Gabriel Valley by a thrust fault.
Strike/slip fault
It arises when shearing forces push two blocks of rocks sideways (horizontally) in opposite directions. Contrary to the above-mentioned faults, in this case there is very little up and down motion. Instead, when the layer of rock breaks, the two pieces of broken land slide past each other in a side by side motion. Although it does not form mountains and valleys, this type of fault causes very strong earthquake. The San Andreas fault is an example of strike/slip one.
What Influences Climate?
What influences climate? It is a question that many people ask. Well, the weather patterns of the different regions of the Earth are influenced by several factors, not by only one. These nature's elements, which contribute to the yearly climate of a territory, or country, are the following:
1- The winds. They could bring humid, dry, cold, or warm air. A mass of humid warm air produces rain when it collides with a mass of dry cold air.
2- Ocean currents. They influence the temperature and even the rainfall patterns of coastal regions. There are two types; warm and cold. The Gulf Stream, for example, is a warm current, flowing from the Gulf of Mexico in a southwest-northeast direction. It reaches the northern coast of France and the Southern coast of England and Wales, influencing the weather of these countries. This is the reason why England is not so cold in Winter as it is in central Russia, even though they both lie on approximately the same latitude.
3- Mountain ranges. Chains of mountains influence considerably the climate of a region, because the act as natural barriers that block and hold back the winds. Usually, they determine the formation of two weather patterns, with one side of the mountain range being humid with rain forests, and dry and desert on the other side. One example is the Blue Mountains of Australia, which act as the natural boundary between the rain forests and the Australian Outback, which is very dry, like a desert.
4- Latitude. It determines how far a city or country can lie from the equator. The farther a region lies from the Earth's mid line, the less sunshine it will receives, especially in Winter time. Thus, countries such Finland, Russia, and Sweden are very cold in winter, while Brazil and Ecuador are not cold at all, because the lie on the equator, which is the imaginary line that divides the Earth into a northern and a southern hemisphere.
5- Altitude. Almost everybody knows that temperature starts dropping when we begin climbing up a mountain. For example, on a Summer day, the temperature of Argentinean city of Mendoza, which lies at the foot of the Andes Range, might be 35 degrees Celcius (about 100 F.) but it could be -20 degrees on top of the Aconcagua Mt.
Earth Geological Layers
The Earth geological layers were formed slowly over hundreds of millions of years. This planet is five billion years old. At the beginning, it was a glowing ball of molten rocks and minerals. As it cooled off, the different geological layers were formed amid volcanic eruptions, earthquakes and other natural phenomena. Today, the science of geology has estimated that the Earth has five geological layers:
1) Inner core. It is the innermost layer, which is made up of solid iron. Its thickness (radius) is about 1,300 km (800 miles). The Danish scientist, Inge Lehmann, determined it was solid by studying the seismic waves that are produced by deep earthquake. It has 1.5 % of the planet mass. Although, it is solid, this ball of iron generates heat.
2) Outer core. It consists of liquid iron and has a thickness of 2,200 km (1,367 miles). It is the source of the Earth’s magnetic field, which is vital for man’s orientation when traveling. It constitutes about 30% of the planet mass.
3) Lower mantle. It is composed of silica (quartz, sand, and flint) and a small amount of iron. This layer has a thickness of 2,500 km (1,553 miles). Its main activity is convection, which is the slow movement of subcrustal materials, transferring heat from the outer core to the surface. It has about 55% of the Earth’s mass.
4) Upper mantle. It is formed almost entirely with peridotite, which is a granular, plutonic igneous rock. It has only 13% of the mass of the Earth as it is 350-km thick (217 miles). Its activity is plate tectonics, which cause the continental drift.
5) Crust. It is made up entirely of granite and basalt, which are igneous rocks, which are hundreds of millions of years old. The main geological activity of this layer is earthquake. It is also called lithosphere, with litho– meaning ‘stone’. Different kinds of sediments top off the crust.
Below, a diagram of the Earth layers. From ‘Simple Geology’
Tectonism in Geology
Tectonism in geology is the science which deals with the constant movements of Earth's top structural layer, which is called lithosphere. Earth’s lithosphere is composed of rocks of varying density which drift as relatively rigid plates. Some of these geological plates are continental in origin; some are oceanic, and some, like the South American plate, a mixture of both continental and oceanic rocks.
These plates movements are caused by deep-seated forces, such as convection in the upper mantle, and crustal forces through push and pull mechanics between plates. Crustal displacement, augmented by magmatism, erosion, and deposition, trigger complex three-dimensional patterns.
In the history of Earth, plate architecture has changed over geologic time, but at this moment Earth’s lithosphere consists of seven major plates, including the South American plate, and numerous smaller plates and slivers.
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