The changing climate has become a hot topic of discussion these days. The mushrooming climate experts have been linking the contemporary vagaries of weather to global warming and the consequences thereof. And dump most of the brunt of global warming on the human interference – their industry, atmospheric pollution due to thermal power generation, vehicles etc.
Well, the objective of this article is not to challenge the views of the experts, but to highlight the fact that the climate in the past too has played truant, while we were in the infancy of our civilization.
A journey through the pages of the earth’s history sometimes unfolds most interesting things. These pages are not accessible to a layman. One needs to read and decipher the cryptic pages with the help of several tools. Amongst such tools, phytoliths are slowly gaining popularity amongst the palaeontologists and paleoclimate experts. Some of interesting and intriguing questions, like, what our ancestors ate or when they exactly became cultivators are some of the information derived from the study of phytoliths.
A view of petrified wood
It is elementary knowledge that silica is present in the soil. Some plants have the ability to absorb this silica. It travels through the plants body and gets deposited in the intercellular and extracellular structures of the plant. This silica, after the death of the plant, gets re-deposited in the soil as phytolith (from Greek: Plant Stone). It attains a definite shape and size while in the plant’s body. Phytoliths were first reported by a German botanist named Struve in 1835. In the course of history, the study phytoliths went through different phases like, botanical classification, ecological research and now as a tool for archaeological and paleoenvironmental research. The latest studies have proved them to be a dependable tool for developing paleo-ecology, environment and a means of vegetative reconstruction. Being heavier, they sink to lake bottoms often reaching the lake via stream draining into it or with soil washed down into the lake during rains.
One such lake, Lahuradewa exists in the interfluve of the rivers Ghaghara and Ami; close to the archaeological site at Lahuradewa village in Sant Kabir Nagar district, U.P. Anju Saxena and Vandana Prasad, Scientists of Birbal Sahni Institute of Paleobotany, Lucknow with Prof. I.B. Singh of Centre of Advanced Studies in Geology, Lucknow University studied the phytoliths from the lake sediments to reconstruct the past climate. Their objective was to reconstruct the rainfall pattern and climate changes in the past 12000 years.
The results obtained from the study were astounding! The phytoliths collected from various depths of the lake and near surface parts indicated presence of varieties of grasses. To a layman, all grasses look alike. But the botanists have classified all the plants including the grasses into families and subfamilies. Phytoliths of particular type are associated with a particular family or subfamily. Based on this information it is known that, phytolith morphotypes belonging to subfamily Panicoidae indicate warm and humid climate; whereas, those of Chloridoidae indicate warm and dry climate; and Festucoidae indicate cool and moist climate, say Anju and her co-researchers.
It is worth explaining that while collecting data or proxy data from the land surface, on climate change, lake sediments give the most reliable information. These sediments generally remain undisturbed hence the reliability. On the other hand, phytoliths being comparatively more susceptible to climate variations keep a truthful record of the ups and downs they have undergone. The accumulation of sediments in a lake is a direct product of climate. More rainfall means more sediments and a scorching Sun with less or no rains means evaporation and even desiccation of the lake. Use of phytoliths in paleo-environment reconstruction has yet to gain popularity says Anju.
Normally it is presumed that a diverse assemblage of phytoliths or for that matter any other evidence must have come from different places. But in case of Lahuradewa lake, opposite is the case. Since the lake is not connected to any active channel of a river, present or past. The lake has a limited catchment. Hence Anju and her co-researchers have surmised that the phytolith assemblage recovered has come from the area surrounding the lake. From a rich assemblage of sedges (Cyperaceae) in the lower part of phytolith succession established by these researchers has given them enough reason to assume that the lake was initially a big marsh.
While working on a crime scene, the forensic scientists do not rely on single evidence only, especially if the evidence available is an indirect one. Likewise, when climates of periods in terms of thousands of years are being worked out the singular evidence of phytoliths may not be quite acceptable. Fortunately for Anju and her co-researchers the phytoliths of the lake profile corroborate with the paleoclimate records in the other parts of the Indian subcontinent.
As already said, to begin with Lahuradewa was a marshy area, a fact well supported by warm and moist climate. It would have continued to be a marsh, but 10300 cal. years BP (calibrated years before present) dry conditions set on. This arid phase of climate lasted for ~1100 years, up to 9200 cal. Years BP. Just imagine 1100 long years of drought! This evidence from phytoliths is strongly supported by the palynological studies (study of preserved pollen and spores), which indicates reduced rainfall during this period. Not satisfied with local evidence, Anju collected information of Bay of Bengal, where drill cores had been collected to develop a past climatic record. That area too was in the grips of dry climate during 10500 to 9900 Cal years BP.
Such dry or extremely wet episodes may affect the human population adversely now, but in the years gone by our numbers were much less. But the climate never remains the same. Monsoon intensified during 9200-5300 Cal years BP and the phytolith record of Lahuradewa correlates well with the records of the Bay of Bengal, Arabian Sea and those from the Himalayas. The wet period between 7000 and 7500 years BP is often referred by past climate experts as the Holocene (starting from 10300 years BP till present) optimum. A strengthened monsoon around that period has also been recorded at other places too. For example, Anju says, ‘Multiproxy studies of Sanai Tal deposits of Ganga plains also suggest of a strong monsoon around 7000 years BP. Even Thar Desert experienced more rainfall and thus a lake was formed in the eastern margin between 9000 to 7000 years BP, which dried periodically, indicating a fluctuating monsoon.
Lahuradewa Lake certainly had human interference too. As confirmed by the presence of Trapa (water chestnut) and Canabis sativa (hemp), (as a source of fibre, seed oil and food). Presence of human activities in that period indicates that the monsoon had ameliorated to allow humans to settle there. In other words, there were periods of less rain at some places even during the era of heavy rains.
In the climate record of Lahuradewa as established with the help of Phytoliths there were five wet phases and four dry phases alternating with each other. As already stated the first dry phase was between 10300-9200 Cal. Years BP. The second phase was 5300-4100 Cal Years BP. The third phase was 1650-1200 Cal Years BP and the last one was 950-700 Cal Years BP. The period in between was marked by wet phases. Out of the four dry phases, the one between 5300-4100 Cal years BP was most prolonged one. It is but natural that during this prolonged drought of 1200 years, the human settlers at Lahuradewa must have migrated to a better place.
Imagine a scenario of such a prolonged drought in the present age! The results would be disastrous. We have to learn to conserve water for the posterity.
We do blame our industries and other polluting agencies for the environmental problems. To some extent it is right too. But we should always remember that the nature is much more powerful than puny humans. It can always change and cause situation of extremes-like extreme rains and extreme droughts. Both are equally bad. From the narrative it is apparent that the nature has been playing truant through the ages and it will continue to do so.
Therefore, instead of trying to mend or bend the nature, we better mend our ways.
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