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الجمعة، 5 أبريل، 2013


الجمعة, أبريل 05, 2013

And the earth which splits (with the growth of trees and plants),
(Surat At-Tariq (The Night-Comer):12)
By: Dr. / Zaghloul El-Naggar
  This Qur'anic verse comes in the context of an oath, while Allah (all glory be to Him) is definitely above giving such a pledge. Consequently, this is understood as a device for emphasis on the special significance of the matter by which the oath is given.

 Now what is the special significance of the faulting and rifting of our planet?

  Early commentators on the Glorious Qur'an saw this significance in the fracturing of the soil on watering it properly to give a free, safe passageway for the tender, green shoots coming out from the germinating seeds that are buried in the soil, in the form of sprouting plants, which is very true. Once you place a seed in the soil and water it properly, it starts to germinate and a green shoot starts to penetrate the soil and grow into a fully developed plant, bearing beautiful flowers, delicious fruits and / or magnificent wood. Such penetration takes place through tiny fractures that develop in the soil as a result of its inflation by hydrolysis and warping upwardly until thinning out to the point of fracturing.

 However, Earth Scientists have recently discovered that the Earth's outer rocky sphere (the lithosphere; which is about 65 - 70km thick under the oceans and 10O - 150km thick under continents) is broken up by a network of deep faults (or rift systems) into 12 main rigid plates, added to a number of small ones (microplates or platelets). These plates float on a semi-molten plastic layer known as the asthenosphere (the sphere of weakness) and move freely away from or towards each other, and past one another. At one boundary of each plate (or microplate), molten rock (magma) rises to form strips of new ocean floor, and at the opposite boundary, the plate collides with the adjacent plate and moves to sink underneath it, to be gradually consumed in the underlying asthenosphere at exactly the same rate of sea-floor spreading at the opposite side. An ideal, rectangular, lithospheric plate would thus have one edge growing at a mid-oceanic rift system (divergent boundary), an opposite edge being gradually consumed into the asthenosphere, below the over-riding or colliding plate (convergent boundary) and other two edges sliding past the adjacent plates along a system of transform faults (transcurrent or transform fault boundaries). In this way, the lithospheric plates are constantly shifting position on the surface of the globe, despite their rigidity, and as some of such lithospheric plates are carrying continents with them, such continents are also constantly drifting away or towards each other.

  As an oceanic lithospheric plate is forced under another oceanic or continental plate and its descending part starts to melt, viscous magmas are intruded and squeezed between the colliding plates, while lighter and more fluid ones are extruded at the opposite edge to form volcanic island-arcs. These eventually grow into subcontinents and continents, are plastered to the margins of nearby continents or squeezed between two colliding continents.

  Such divergence, convergence and sliding of lithospheric plates are not confined to ocean basins, but are also found along the margins, as well as within and in between continents. Both the Red Sea and the Gulf of Californiatroughs (which are extensions of oceanic rifts) are currently widening at the rate of 3cm/year in the former and 6cm/year in the latter case. On the other hand, the collision of the Indian Plate with the Eurasian Plate after the consumption of the oceanic plate that was separating them, resulted in the formation of the Himalayan Chain, with the highest peaks on the surface of the Earth today.

  Fault planes traversing the outer rocky sphere of the Earth for tens of thousands of kilometers across the globe, running in all directions for a depth of 65-150km are among the most salient features of our planet. These came to human notice only after the Second World War and were only understood within the framework of the concept of plate tectonics which was finally formulated in the late sixties and the early seventies of the twentieth century.

  These lithospheric faults are a globe - encircling system of prominent rift zones (65-150km deep and tens of thousand km long) along which lithospheric plates are displaced with respect to one another divergently, convergently or sliding past each other. They are also passageways through which the trapped heat below the lithosphere is steadily released, and different magmas are periodically outpouring. Molten magmas in numerous hot spots, deep in the mantle, being less dense, tend to rise up and on relative cooling descend down in the form of hot plumes that create convection currents. Such currents carry the lithospheric plates and move them across the globe, with divergent, convergent and sliding relationships. Divergence takes place at the rising tips of the convection current, while convergence happens at its descending sides.

  During the early history of the Earth, its interior was much hotter (due to the greater amount of residual heat of accumulation and the much greater amounts of radioactive isotopes such as 235U and 4oK) and hence convection was much faster and so were all the phenomena associated with it {such as volcanic activity, Earthquakes, plate movements, mountain-building movements and continental build-ups, (or the so-called ocean-continent cycle or the geosynclinal/mountain-building cycle).

  During these processes, both the atmosphere and the hydrosphere of the Earth were outgassed, the continents were constructed as positive areas above the ocean basin (through the accretion of volcanic island arcs into sub-continents and continents) and mountains were built.

  About 500 million years ago the early continents were dispersed across the surface of the Earth, in positions much different than the ones occupied by the continents of today. Convection currents then operating in the mantle ended up by pushing all the early continents together around 200 million years ago, into a single super-continent (Pangea) above a single super-ocean (Panthalassa).

  The outer rocky sphere of the Earth (or lithosphere) acts as a lid, impeding heat flow from inside the Earth. The gradual increase in this trapped heat produced a great rift system right in the middle of the mother continent, and this rift system propagated gradually through time, separating North America from North Africa (about 180 million years ago) and from Europe (about 150 million years ago), followed by separating South America from Africa (about 110 million years ago) and separating Greenland from Norway (about 65 million years ago), when Iceland began forming.

  When this break-up of Pangea began, a westward waterway from the mother ocean (Panthalassa) in the form of a broad gulf (called Tethys) encroached gradually over Pangea, breaking it into a northern continent (Laurasia) and a southern one (Gondwana). Further fragmentation produced the present continental masses which are currently undergoing more breaking up. The original rift is now the Mid-Atlantic Ridge, whose axis is still an active site of basaltic outpourings similar to many other rift zones along which current sea-floor spreading is taking place.

  Basaltic material has been pouring out gradually from more than 64,000km of mid-ocean rift valleys on both sides of such ruptures in the Earth's crust, since the very early days of their formation. The youngest oceanic crust is always around the deep rift valley and has steadily been pushing older crusts away from it. The age of the oldest existing oceanic crust does not exceed the Mesozoic era (about 200 million years old), and is currently being consumed at the convergent edges of the plates with rates almost equivalent to the rate of producing new oceanic crust at the mid-oceanic ridges.

  Volcanic mountains are also found on the continents such as the isolated peaks of Mount Ararat (5lOOm above sea level), Etna (3300m), Vesuvius (1300m), Kilimanjaro (5900m) and Kenya (5lOOm). These are associated with intra-cratonic, deep rift systems that traverse the whole thickness of the lithosphere, and communicate with the asthenosphere, and hence are currently fragmenting the existing continents into smaller landmasses.

 From the above mentioned discussion, it becomes obvious that the magnificent network of deep fault (or rift) systems (65-150km deep) that encircle the globe for tens of thousands of kilometers in all directions {breaking its outer rocky zone (the lithosphere) into major, lesser and minor plates, microplates (or platelets), plate fragments and remnants} is one of the most striking realities of our planet. Without these deep fault systems the Earth could not possibly have been inhabitable. This is simply because of the fact that it is through such deep faults that both the atmosphere and the hydrosphere have been outgassed and are constantly rejuvenated, continents are steadily built and fragmented, mountains are constructed, the crust is periodically enriched with new minerals, lithospheric plates are moved, the accumulating internal heat of the Earth is gradually and steadily released and the whole dynamics of our planet are achieved.Consequently, such an established fact of the Earth is so vital for its existence as well as for our own survival on its surface that it becomes well deserving to be mentioned in the Glorious Qur'an as one of the signs of the Creator. However, this fact did not attract the attention of Earth scientists until after the Second World War, and was not fully understood until the late sixties and the early seventies of the twentieth century. The Qur'anic account of this established, salient feature of the Earth more than 14 centuries ago, is one of numerous signs that clearly testify to the purely Divine nature of this illustrious Book and to the truthfulness of the Prophethood of Muhammad (PBUH).

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