Day: January 24, 2012

Dr Irengbam Mohendra Singh January 15 2012

A normal science involves the acquisition of experimental data. It requires a certain scientific method in doing so. ‘World of Earth Science’ in 2003 explained the scientific method:

Looking at the scientific model of our planet, it is not always apparent that science can predict the natural events, but a little deeper reflection, usually can reveal the predictive value of any scientific activity.

Scientists have been trying to understand nature. The formulation of the scientific model of Earth has not always been subject to limitation of technique. Scientists can choose any technique. A new technique in postulating new scientific discoveries has been a way of validating new models. This is what is called the scientific method.

Scientists have now scientific evidence for postulating how the earth was formed and how the continents, oceans and everything on this earth were formed though still, it is only a hypothesis. Likewise, Stephen Hawkins’s Big Bang theory is a hypothesis but based on scientific evidence.

For years theoretical physicists postulated the existence of cosmic microwave background (CMB) radiation as a leftover from the Big Bang that occurred 13.7 billion years ago. It was finally mapped by Microwave Anisotropy Probe – a satellite sent up by NASSA. For this,
Pezias and Wilson were awarded Nobel Prize for physics for the joint discovery in 1978.

Alfred Wegner, a German meteorologist in 1912 first put the idea that continents and oceans began to form about 300 million years ago.

He postulated that continents had formed as a single “super continent” from the volcanic rocks. The single land mass was called Pangaea (Greek for “all the earth”). Pangaea had later split due to earthquakes and its pieces had been moving away from each other ever since (Continental drift).

There was only one ocean called Tethys (name of Greek god – mother of Oceanus) that existed between Asia and Australia – Antarctica during the Mesozoic era.

By the late 1960’s geologists, with the help of ocean surveyors began to understand what goes on beneath our feet. The theory of plate tectonics was formed and well supported. In the last 40 years the theory of plate tectonics has enabled scientists to view the mysteries surrounding the formation of continents and oceans.

The Theory of plate tectonics is probably the most important geological hypothesis ever developed, after the Theory of Continental Drift espoused by Alfred Wegner in the early 20th century. The scientific community at that time ridiculed Wegner and flatly rejected his hypothesis.

The theory of plate tectonics was formulated by American, Canadian and British geophysicists. It explains the earthquakes, volcanoes, the formation of mountains, and other
geophysical phenomena to interactions of the rigid plates forming the earth’s crust. The word tectonics derives from the Greek tektonikos, meaning ‘pertaining to construction’.

Dr Robert Ballard at Woods Hole Oceanographic Institution, wrote in 1983: “plate tectonics not only vindicated Wegner, it transformed geology as profoundly as the theories of evolution
(2)
and relativity transformed biology and physics.”

The interior of Earth is divided into crust, mantle and core. According to the theory, the earth’s surface layer, or lithosphere (the upper layer of earth’s interior, including the crust and
the ‘brittle’ portion of the top mantle), consists of seven large and eighteen smaller plates that move and interact in various ways. They converge, diverge and slip past one another creating the earth’s seismic and volcanic activities.

These plates are not fused with each other but they are in constant but slow motion. This is what is known as “Continental drift”. This term is now replaced by “plate tectonics” (plate building).

These plates lie atop a layer of partly molten rock called the asthenosphere. These plates can carry both continents and oceans, or exclusively one or the other. Example: the Pacific plate is
entirely oceanic. The continental plates are lighter than the oceanic plates at the bottom of the sea.

According to John Gribbin, scientist and the master of popular science writings, at the heart of understanding plate tectonics is the discovery that the sea floor is also spreading.

The direct observations from the space, magnetic surveys of sea floor, seismography have produced many lines of evidence that there are cracks in the sea floor where molten materials from beneath the crust (magma) well up to the surface in a ridge, and then pushes out on either side of the crack, where it sets, especially in the Atlantic.

But the reverse destruction of the sea floor is also going, driving down back into the interior of the earth, somewhere, especially under a continent. The Pacific Ocean is shrinking as a result at about the same rate as the Atlantic Ocean is expanding. As these happen far out in the sea these earthquakes and underwater volcanoes do not bother us.

When the hot fluid material from beneath the surface of the earth rises and breaks though continents and cracks them apart, new oceans form, as it is happening in East Africa today. And sometimes continents collide, as the seafloor between them shrinks away to nothing, forming new mountain ranges, such as the Himalayas.

Continental plates are composed mainly of granite, while oceanic plates are mostly basalt, which is considerably heavier. The continents are thus lighter and buoyant and hence float higher on the earth’s mantle than the ocean’s crust does.

The average depth of the ocean is 3,800 m more than four times the average height of the continents, and two thirds of the planet is covered by sea.

John Gribbin says: “It is clear that these processes can only operate on a planet, like the earth, with a relatively thin crust of solid material on top of the fluid layers beneath. Without water none of this would happen; without water, there would be no plate tectonics.”

He says all these processes are necessary for the existence of life on earth. Gases bubble out of magma and rises to the surface, where they are released at volcanic vents, as water vapour,
carbon dioxide and nitrogen. All these gases are used by life on earth, maintaining the balance
of greenhouse gases in the atmosphere and regulate the earth’s temperature.

John Gribbin argues that without the combination of thin crust and water of the earth technology would not have been possible. And without the metals, intelligence alone, the technological civilisation would not have happened.
(3)
There is scientific evidence that more than half of the continental crust that exists today had already formed by 2.5 billion years ago when the earth was struck by a series of major impacts. The rest was produced in just 700,000 years, less than a fifth of its life time to date.

There is direct evidence for these impacts in geological features known as Crations found in some ancient rocks. And there is indirect evidence from the battered face of the moon, from which astronomers can estimate how many impacts of different sizes affected the earth and its neighbour moon during different intervals of geological time.

Gribbin put this in perspective: the asteroid implicated in the death of dinosaurs some 65 million years ago was only 10 km across. The incoming piece of debris, say, at a speed of 20
km per second, would smash straight into the underlying crust, generating so much heat that it
would melt the surface of the earth into a lake of liquid rock, perhaps 400 km across.

The theory is very attractive by no means certain that plate tectonics helped tremendously in continent building. This is similar to my theory of the origin of Meitei language. At such a distance in time, any explanation must be speculative. One can take it or leave it. There is no point in arguing unless one has a more plausible hypothesis.

Andrew Glikson, of the Australian National University has a plausible explanation, but it is rather mouthful and is beyond the compass of this article.

The old theory of Wenger was right but he could not explain exactly how the continental drift had occurred. The answer now, is the plate tectonics.

The plate tectonics is new and widely accepted theory. It provides a convincing explanation of such phenomena as continental drift, earthquakes, mountain formation and volcanic eruptions. It explains the processes that have shaped the Earth in terms of plates and their movement.

The significance of plate tectonics as the “unifying theory” is emphasised by its inclusion in the book, The Five Biggest Idea of Science. Alongside plate tectonic theory there are four other monumental ideas: (1) the atomic model; (2) the periodic law, (3) the big bang theory; and (4) the theory of evolution in biological sciences.

Plate tectonics is now accepted as ‘central requirement for life on Earth because it is necessary for keeping the planet supplied with water after it supplied it with land. Without continents there would be no humans and Americans (NASA) would not have sent a
Mars Rover atop a rocket to Mars on November 2 2011, in its eight and half months’ journey to find life on it.

The writer is based in the UK
Email: imsingh@onetel.com
Website: www.drimsingh.co.uk

Read more / Original news source: http://kanglaonline.com/2012/01/plate-tectonics-how-the-continents-and-oceans-were-formed/