The global warming episode has left us worried about the future of our sub-continent. The fear of melting ice and anticipated rise in sea levels makes one shudder with the thought of submerged coastal habitations and ruined flood plains. In other words it means that our coast line would change. Ports would be submerged and even many a habitation on the coasts may be lost for ever! One ponders whether the climate of our planet has been like this only ever since it came in to being or was it different!
Let us go back in time by some 360 to 340 million years. That was the Paleozoic Era of the earth's history. The geography of our planet then was completely different than what it is today. There were only two major continents. One called the Gondwana which included what are now Africa, South America, Australia, Antarctica and India. The other included the North America and much of what is now Eurasia.
Around 295 million years ago (ma) the Gondwana continent while it was still close to the South Pole underwent continuous change with respect to environment, climate and geography including latitudinal conditions. Unlike present day when conditions are getting hotter and hotter everyday, those days wide areas on the surface of the earth were facing the brunt of the freezing cold. There was widespread glaciation. Known as the Permo-Carboniferous glaciation, it has left its own tell tale marks.
Mary E.C. Bernardes-de-Oliveira and Sandra E. Mune of USP-Institute of Geosciences, Brazil, along with Rosemarie Rohn from UnG Post Graduation Research and Specialization Centre, Brazil, Fresia Ricardi-Branco UNESP-Institute of Geosciences and Exact Sciences, Brazil and Rajni Tewari of Birbal Sahni Institute of Palaeobotany, Lucknow, India joined hands to find out the extent of Permo-Carboniferous glaciation and its impact on plants.
It is known that there have always been hot and cold climatic spells. Thus while large areas of the earth were under deep freeze, some parts were experiencing a warmer spell. Warmth meant life. Thus the sediments deposited between two glacial phases carry the remains of plant life that existed then as fossils. Plants being more susceptible to climatic vicissitudes flourish or perish as per the climate.
Large areas of Gondwana continent have registers of movements of glaciers from the centre-south of Africa in direction to the southeastern region of the South America, from Antarctica towards the southwestern region of Australia and from Antarctica to the region north-northeast of India say Mary and her co-workers. The glaciation on one hand while it had frozen the environment at the poles, the subtropical regions faced droughts.
Mind you all these changes in the environment were not happening overnight. The deep freeze or the global cooling spell was there for millions of years. Today while talking of the climate we think in terms of yearly changes or at best decadal changes. The instrumental record tells us about century level changes. It is only the floral, faunal record and of course the tell tale marks on the rocks and also the oxygen isotopes that give us information about the conditions that were prevalent millions of years ago.
Amongst these evidences it has been found that the environmental changes of the past are best reflected by the fossils of animal and plant kingdoms. Plants are more susceptible to climatic changes. We read in reports each year that the crops worth several crores of Rupees perished in drought in various parts of the country. Similarly the drought in the subtropical regions during the Permian glaciation caused extinction of many forms of plants, record Mary and her colleagues.
We know that plants need moisture and sunlight apart from a nutrient rich soil. When everything is under a thick cover of ice, plants that too larger varieties like palms etc can not survive. Conditions change as soon as the glaciers withdraw. With the availability of ground moisture, sunlight and proper soil plants re-emerge. This is the usual scenario of an inter-glacial phase which may last for thousands of years or even more.
Nature seems to be a ceaseless worker! Withdrawal of glaciation phase means development of other environments like fluvial, deltaic, lacustrine and marine. This is what exactly was happening in the Gondwana land some 300ma. In other words flora typical of a given environment had started to appear. Since many species became extinct, many had evolved further in the natural process of evolution spanning long periods. Frequent glaciations caused many of the basins to lose continuity. Hence when the plants reappeared many species became restricted to an area or province. In other words they developed a provincialism.
Mary and her colleagues have been able to identify specific associations from the inter-glacial sediments of Brazil, Argentina, Africa, India and Australia. Thus furthering the conjecture that there was a time when all these places were part of one and the same land.
Widespread glaciation reduces the level of CO2 in the atmosphere. D.J. Beerling of the University of Sheffield, U.K. had with the help of cuticles of plant remains established that during Permo-Carboniferous period (300-250 ma) when the longest and most severe of glaciations had taken place CO2 levels from the stomata of plant remains was abnormally low. Stomata are the pores on plant leaves through which the plant virtually 'breathes'. He published his finding in 2002.
Actually around 370 ma the Gondwana began to drift southwards and went closer to the South Pole. Levels of CO2 were low on the ice covered South Pole. This triggered the process of glaciation on the Gondwana Land. Global cooling is most effective when continental ice can form. Because the continental ice can be several kilometers thick, whereas sea ice on the sea may be only tens of meters thick. Thus with the passage of time the Gondwana began to feel the brunt of the deep freeze and became a frozen continent. As the Gondawana began to wander northwards there was lack of continental ice. Gradually the thaw set in.
But the nature never sits idle. Once again due to lowering of CO2 levels in the atmosphere yet another major glaciation took place around 345 ma. But it did not last long. After 10 million years a warm phase started. For ten million years life reappeared on the Gondwana land. However, the fatal blow came some 325 ma. This time the glaciation was at its peak. It lasted for 70 million years.
Imagine an Ice Box that brought everything to a stand still for 70 million years! Imagine the impact on living beings! It was a life less era.
Today we are bothered with the thought about global warming and its impact upon our future generations. But if you ask me I am not that much worried. Because warmth means life, but cold is nothing but death.
The question that haunts me is whether the human race will be able to survive that cold or our like the mammoths our frozen remains too would be 'discovered' by the scientists of the future?