BEFORE we proceed further, we must bear in mind that our planet Earth is billions of years old — around 4.5 billion years. Some features are older than the others.
For instance, the oceans are a bit older. The land portions as we know and understand, such as the continents, are a bit younger. This is of course different that here ‘just a bit’ works out at a few million years. Mountains and the great mountain ranges are not only much younger but still growing; that includes our majestic Himalayas.
At one time, all the land lay converged in one place, called Pangaea (Greek for ‘all land’). It would take the sustained action of natural forces to break apart one land mass into many pieces, or plates that would ‘float’ and drift into the ocean at a very slow pace. Ocean or no ocean, these would still drift, in six large pieces and later, into 12 or so smaller pieces — driven not by water but magma in liquid form residing in mantle, just below the crust.
The thrust of magma is very forceful. Stronger than anything, the crust has to offer resistance. Whenever, and wherever the powerful magma finds vents or cracks, it finds its way upward through the crust.
But prior to this sort of coordinated movement, portions of earth, call them flakes, were there roaming aimlessly. Millions of years, later a specie would emerge and would lay claim to these pieces of real estate and give them such fanciful names such as America, Asia, Australia, Europe and so on. But it is a matter of opinion, or conjecture to believe that this happened several times since the Earth came into being some 4.5 billion years ago. Three, four or may be five times, you never know. After all, what would stop the Earth from repeating its ways?
Nevertheless, it is difficult to imagine that such action could have repeated itself time and again, yet some scientists do believe that Pangaea occurred again and again, and yet again.
So, let us presume that initially there were just the oceans; the land area converged in one place besides some, nondescript wildlife some 300 million years back when the huge land mass began to crack and break up into smaller, yet large segments, as indicated before. By 200 million years back, the shapes of continents had begun to emerge in pretty much the same fashion as would be identifiable later on.
Consider a little piece of rock lying idly by the wayside along the highway, or outside your house. Whatever the reason for its presence, the fact is that once, perhaps many million years ago it was a part of a great boulder up in the highlands, which itself was part of a yet greater mountain. Acted upon by inexorable forces of nature — bright sunshine, rain, dew, wind, flowing water, frost, heat waves, snow, cold air etc., the mountain cracked and broke apart into fragments, big at first then tiny pieces and eventually sand grains. These were carried by flowing water, and by the contour of the Earth to places far away. Eventually, it lay there along the highway or outside your house....
Wind played its part too. Some grains were deposited along the planet’s numerous sandy beaches. This action of nature is called erosion. Erosion has forever brought changes on our planet. It is taking place everywhere, every moment of the day, forever. We’ll discuss more about erosion at appropriate places later on.
The most beautiful of all planets is also a piece of paradise. Blue, green, turquoise ball with white, wispy clouds hanging overhead. It has everything: deep blue waters, silvery sands, huge rivers, green mountains here and they are covered with snows, dense forests, valleys, rolling sand deserts, grassy plains and that lovely and unique handiwork of nature — human beings, besides those millions of species of animal. A close look at planet Earth will reveal a lot more. Planet Earth is much like an onion, though not exactly. Its layers are secretive, yet revealing to the discerning eye.
At the time the Earth was growing in mass, it kept accreting rogue material from space, thanks to its gravity or chance encounters with loose debris roaming in space aimlessly, waiting to be scooped up. As matter kept gathering (accreting), the size kept becoming larger and larger still. Due to impacts and recurring shocks, the mass which was fluid, gradually became plastic. Metals (heavy matter) sank to the bottom and lighter material or silicates floated upward, until the sunken material became one big ball with an identity all of its own, we will call it the core — the inner core and the outer core.
The inner core is hot and bears the brunt of a great deal of pressure from all around. It is made up of heavy material, the analyses of the interior, whether the core or whatever else, is not possible except for the seismic waves (that is, study of the earthquakes).The inner core is found to be hot, very hot but not fully molten., though the upper part of the inner core is. Then there is the outer core. It is again very hot, and in circulation, inexorably and grinding slow in speed.
Mantle comes next, which is the layer of dense rock and metal oxides that lies between the molten core and crust. It is not molten but not solid either. It behaves like plastic. Mantle is 84 per cent of the Earth’s volume.
Rocky crust is quite thin; about 70km under the continents at the maximum but only 5-10km under the oceans, because of its lower density it floats on the denser mantle.
It is where we live. It is where all the oil, gold, diamonds, metals and water deposits are. Even though oxygen is 21pc of atmosphere, the story of surface material is somewhat different. It is 47pc oxygen, 28pc silicon, 8pc aluminium and 5pc iron, with traces of magnesium, calcium, potassium and some other elements.
Although the crust may occupy a tiny portion of the whole (average depth 32km as against 12,756km), like the egg-shell is to the egg, yet it plays a dynamic part in the whole game. It moves continents.
The hidden force behind the moving continents is the magma which is riding on the back of mantle. Applying uneven force on various portions of crust from below has caused cracks in the crust at various places. This led to the independent movement of the portions carrying large segments of land, together with all features of land, whether rivers, lakes, valleys, mountains, animals and whatever else. The oft-recurring fissures in the crust often cause havoc. Who is not aware of earthquakes and the outflow of lava which keep visiting our planet? The width of inner core is 2,700km; the depth of outer core is 2,090km, and that of the mantle is 2,900km.
When Pangaea began to break apart 200m years back it did so in six pieces called, plates. Up until that moment all continents had stayed huddled together. One look at the world map will tell the story. How big and small islands, their shorelines and other chunks of land fit into each other like a huge jigsaw puzzle. Often smaller examples offer a more graphic picture: Madagascar seems to have broken away from the master continent, Africa, which itself is breaking up in the middle. Continents will keep drifting; some will come closer, the others will drift away.
Fortunately, the speed of this drift is too slow to make any difference in the duration you read this write up. It will take a few million years to become discernible.
Meanwhile, ‘petty’ earthquakes will carry on pounding various portions to keep reminding us that the worse maybe far into the future, but small and manageable disasters are just ‘round the corner’.
Fortunately, too, that by the time the force or thrust of the ominous magma reaches the top of crust, it has dissipated its energy by far. The continents move at miserly 4-8 millimetres per year; the same speed at which our nails grow. Interesting facts about continents and our very own subcontinent remain to be revealed.