ABSTRACT
Our understanding of the formation of the continents has been revolutionised over the last few decades. The Earth’s outer crust is now thought to be made up of fairly rigid plates – of differing sizes and irregular shapes – which have been moving relative to each other for at least 1,000 million years. About 400 million years ago these were grouped together in one piece – a super-continent called Pangea. This split into two parts – a Northern part known as Laurasia, and a Southern part called Gondwanaland. Between the two lay what is known as the Tethys Sea – which remains now in the remnant string of ‘middle earth’ seas – the Caribbean, the Mediterranean, the Black Sea and Caspian and the trough of the Ganges Valley. Both the Northern Laurasian part and the Southern Gondwanaland part then split. One split common to both runs down the middle of the two Atlantic oceans – so the fact that the eastern coastline of the Americas ‘fits’ the western coastline of Europe and Africa is not an accident. The Atlantic split is not the only split that occurred in the Southern part – Gondwanaland. The Antarctic broke off and drifted towards the south pole, Australia drifted Eastwards (relatively) and about 200 million years ago what was to become the Deccan block broke off, and began to drift across the Indian ocean (Figure 1.1). For more than 100 million years it was isolated – hence its flora and fauna could evolve in a distinctive manner similar to that of Madagascar and Australia. Then about 80 MA (million years ago), it struck into the Southern flank of Laurasia (Figure 1.2), and began to push the edge up – lifting the Tibetan plateau and beginning the process – which has not ended – of pushing up the Himalayas, partly from the sea-bed rocks of the Tethys Sea. So what had been a fairly straight line from the Straits of Hormuz at the mouth of the Persian Gulf to Malaysia became severely dented. The Deccan Block is still pushing north at about 6 cms a year – so the Himalayas are also continuing to rise – at an average of between 1 and 9 cms a year. The front ranges, the Mahabharat that separates Kathmandu from the Indian plains and the Siwaliks, began their uplift 200,000 years ago – well within the time period of human settlement – and so recent in terms of Earth history that if the earth has lasted for one year, then this event started in the last 23 minutes.
