A CONTINENTAL DRIFT

RECONSTRUCTION OF THE CONTINENTS
Euler's theorem states that the movement of a portion of a sphere on its surface is defined solely by a single angular rotation around a pole of rotation. The pole of rotation and its antipode at the opposite end of the diameter are the only two points that remain in a fixed position with respect to the portion in motion.
Consequently, the movement of a continent on the earth's surface up to the position pre-drift can be described by its pole and the angle of rotation.
GEOLOGICAL EVIDENCE OF CONTINENTAL DRIFT
The continental reconstructions are based solely on geometric correspondence of the edges of the continental shelf. If these are really the ancient shapes of the continents, it should be possible to monitor geological continuous from one continent to another through the limits. The continent, breaking, would have interrupted the continuity. Not always, though, the split or rift truncates the oldest geological structures, because sometimes occurs along lines of weakness in the supercontinent that are / / the grain structure, or to the geological features.
Paleoclimatology
The distribution of the provinces climate on Earth is controlled by a complex anterazione of many phenomena, including insolation (ie, latitude), the direction of the winds, ocean currents, altitude and topographic barriers. Most of these phenomena is not well known in the geologic record. In general, however, the main factor is the latitude climate control, ignoring small combinations, the study of climate indicators in ancient rocks can be used to deduce, in general, the ancient latitude. As a result, you can use the paleoclimatology, the study of past climates to prove that the continents have drifted, at least in North-South direction.
The indicators are:
1.Carbonati and deposits on the rocks: they are limited to the presence of hot water
2.Evaporiti: formed under hot and arid regions where evaporation> precipitation
3.Strati red: red continental sediments oxidation
4.Carbone and oil are formed by the accumulation and degradation of organic remains, requires a hot and humid climate
5-6-7-8 phosphorite, bauxite, desert deposits, glacial deposits
The results obtained by applying these techniques paleoclimatic strongly indicate the latitude continents have changed over geological time.
THE CONTINENTAL DRIFT AND Paleontology
The continental drift has influenced the distribution of ancient animals and plants, creating barriers to their dissemination. A clear example of this phenomenon is the growth of an ocean between two parts of a supercontinent ocean would prevent terrestrial life forms to migrate between the two separate blocks. A less obvious diffusion barrier is represented by the climate, such as the movements of the continents in the sense of latitude can create climatic conditions are not suitable for certain organisms.
Paleomagnetism
The science of paleomagnetism is the study of the fossil magnetism preserved in some rocks. If this megnetismo originated at the time when the rock has been formed, you can use the measurement of management to determine the latitude at which the rocks originated.
Paleomagnetic techniques make use of the phenomenon by which certain minerals are able to maintain a record of the direction that the Earth's magnetic field had in the past.
Some paramagnetic compounds containing unpaired electrons in large numbers are called ferromagnetic. The magnetic structure of these substances tends to take place in a number of magnetic domains, in which the atoms are coupled by the interaction of the magnetic fields of the unpaired electrons.
REMAINING NATURAL-MAGNETIZATION
Rocks can acquire a natural magnetization remaining MNR in many ways. If the MNR is formed simultaneously with the rock is called primary if it is acquired during its subsequent history, secondary.
The remainder of the primary igneous rocks is known as magnetization termorimanente MTR, is acquired while the rock cools from the molten layer to below the Curie temperature, which takes place after the solidification. At this point, the ferromagnetic minerals present assume a magnetism in the same direction of the geomagnetic field of the moment which will be retained in the subsequent history of the rock.
The remainder of the primary clastic sedimentary rocks is known as detrital remanent magnetization MRD. Since the sedimentary particles are deposited through the water column, any ferromagnetic minerals present aligns in the direction of the geomagnetic field, if the particle is not too heavy. After the burial, when the sediment, saturated with water, is in a liquid state, the magnetic particles realign to the geomagnetic field following activities microscopic, and this orientation is maintained when the rock solidifies.
The rock may acquire a secondary MNR, possible mechanisms are different.
Is acquired a magnetization chemo-remaining MCR if ferromagnetic minerals are formed as a result of a chemical reaction such as oxidation.
The isothermal remanent magnetization MRI occurs in rocks which have been subjected to strong magnetic fields, such as the outbreak of lightning.
The remanent magnetization viscose MRV can be produced when a rock remains in a relatively weak magnetic field for a long period of time, so that the magnetic domains are loosened and acquire the direction of the external field.
The MCR, MTR, MRD tend to be hard and stable for a long time, as for example the MRV tend to be tender and to be lost quite easily.
-CURVE OF MIGRATION OF APPARENT POLES
The paleomagnetic data can be shown in two ways.
In the first you draw the continent in successive positions according to the age of sampling sites.
In accordance with the continent is considered fixed and there represent the apparent positions of the poles for different times, so as to delineate a path of migration of apparent poles, MAP.
The paths MAP can be used to interpret the movements, collisions and dismemberment of the continents.

THE CYCLE OF WILSON
The Pacific Ocean has opened about 300 million years ago and will close completely between other 200mA, then the lifetime of an oceanic basin is 500 Ma processes of plate tectonics, however, are active from 2500 But perhaps ago as a result, there would have been many cycles of creation and destruction of oceans in Earth's history. Very little remains of these ancient oceans, such as the association of ophiolites.
The frequency of opening and closing of the oceans is known as the Wilson cycle.
Say there are two continents AB and CD. The ocean is expanding AD, BC contracting. A bit 'of time after the ocean BC closes completely, and this phase of the movement of the plates concludes with the collision margins B and C, the construction of a chain-type Himalayan along the suture BC and the formation of a supercontinent AD.
The ocean AD needs to include subduction zones at its edges to maintain the surface area of ​​the globe, even if you do not know the reasons for which the subduction begins: it does not seem, however, that the cause is the sediment load.
The strength of the suction pit undergoes stress the supercontinent AD. If the other conditions are still present, the supercontinent will crack at B'C ', not necessarily along the suture previous BC. Now the two continents AB 'and C'D separate inmiddle with a new ocean expanding B'C' and, to compensate for the newly created oceanic lithosphere, ocean AD must begin to shrink continuously developing subduction zones at the edges Continental A and D. This phase will continue until the collision of A and D.
Vink and others have demonstrated that the resistance of the continental lithosphere decreases with increasing thickness of the crust. Consequently, the great thickness of the crust in the areas of the suture makes probable site of rifting future.
The cycle of Wilson will continue to operate until the concentration of radioactive elements all'inetrno of the Earth will not become too low to provide thermal energy sufficient to power the movement of the plates.
Gurnis performed numerical simulations of the aggregation and dispersion of continents and postulated that the plate motion during the Wilson cycle is intermittent and not continuous.
The author argues that the continents tend to aggregate in excess of cold downdrafts in the mantle, where they act as a blanket insulation. Consequently, the mantle heats up, altering the course of the convention, and the supercontinent breaks as a result of the effort that results. Thus, the fragments of the continent moving towards the new cold downdrafts produced by the new regime convection.
Gurnis Stresses that the continents, except Africa, are moving into cold regions of the mantle characterized by areas of low geoid, a few hot spots and high seismic velocities.