By Afroz Ahmad Shah
How do the earth scientists know the internal configuration of Earth? These people obviously cannot enter within the deeper sections of Earth; therefore, whatever we listen to or read about the internal structure of Earth is through indirect means. It is like an X-Ray of our body. The best way scientists have achieved it is through the paths and characteristics of seismic waves (Earthquake waves) travelling through the Earth. Today there are several other methods available to investigate the characteristics of the Earth’s internal arrangement.
Based on these studies, the Earth is said to be composed of three major layers, which are of different composition and physical properties: the core, the mantle, and the crust. The upper part of the mantle and the crust together constitute the Earth’s outer shell, the lithosphere (litho= rock). This layer has fragmented the entire Earth into a number of big and small pieces, which move and interact continuously. These pieces are called the Plates and there are 7 major fragments, which are as follows: Africa, Antarctica, Australia, Eurasia, North America, South America and Pacifica. Apart from these big pieces, there are a number of minor ones like Adria, Arabia, Caribbean, Nazca, Philippines, Woodlark, Solomon Sea and others.
The upper part of the mantle and the crust together constitute the Earth’s outer shell, the lithosphere (litho= rock). This layer has fragmented the entire Earth into a number of big and small pieces, which move and interact continuously. These pieces are called the Plates
The plate tectonic theory was born and with it the rationality to explain the various geological phenomenon, which have been speculated for centuries together, for example the formation and breakup of continents, oceans, the formation of mountain ranges, earthquakes, volcanoes etc. Now we fairly understand that the present configuration of the world was attained slowly and over a period of millions of years. It is believed that at about 225-200 million years ago, the supercontinent, called Pangaea (meaning “all lands” in Greek) began to break apart forming Gondwana (South America, Africa, India, Antarctica, and Australia) in the south and Laurasia (North America and Eurasia) in the north. This occurred because of the opposing movement of the two resulting supercontinents along a spreading centre, located at the bottom of the Tethys Sea, the body of water between Gondwana and Laurasia.
Over geologic time, the interactions of different plates together with other geological processes have created some of nature’s splendid landforms, for example, the Himalayas, the Andes and the Swiss Apls. However, it has also created terror and devastation in the form of earthquakes, tsunamis and volcanic eruptions, which have killed tens of thousands of people over the decades. The Japanese and Turkish Earthquakes are the two very recent examples of such devastations.
It is now known to Earth scientists that most earthquakes and volcanic eruptions do not occur randomly on the Earth, but, are distributed along certain well defined areas, which are mostly along the boundaries of plates. For example, the Indian and Eurasian plate boundary, where the Indian plate dips down the Eurasian plate and causes earthquakes. Similarly, the circum-Pacific Ring of Fire, where the Pacific Plate meets many surrounding plates is the most seismically and volcanically active zone in the world. This plate interaction is said to occur, because of the continuous motions of the plates, which is primarily driven by the heat within the Earth. This has caused the destruction and the formation of new oceans and continents worldwide and has given world the present configuration, which resulted from such movements over a period of millions of years. This process if continued at the present rate will reconfigure the shape and size of the globe and the world will probably look like this (Figure B).
Afroz Ahmad Shah is a research fellow at Earth Observatory of Singapore, Nanyang Technological University, Singapore.