The past climatic changes always played a crucial role in shaping the humankind. Understanding the past climatic changes vis-à-vis archaeological cultures is a major area for the archaeologists. The long-term climate dynamics in the past, especially the monsoon in the Indian context is essential to also understand the emergence of domestication of floral species.
The archaeologists employ different strategies to understand the human interaction with the climate, ecology. This consists of palaeobotanical investigations with the aid of biological proxies like pollen, diatom, phytolith, which helps both in understanding the climatic changes as well as palaeodietary practices.
The study of charred grains from archaeological context is another area of palaeobotany, which is extensively used by archaeologists to reconstruct the palaeo-diet right from the beginning of domestication of plants.
What is a phytolith?
Phytoliths are rigid, microscopic structures made of silica, taken up from the soil, whereupon it is deposited within different intracellular and extracellular structures of the plant. They vary in shapes and sizes. They are identified on the morphological basis and thus the taxanomical differences in phytolith are very important.
What is pollen?
Pollen is reproductive unit of plants ranging from 5 – 500 mm in size. Pollen is fine to coarse powder containing micro-gametophytes of seed plants, which produces male gametes. The vegetative and generative cells are surrounded by thin delicate walls of unaltered cellulose called endospore or intine, and a tough resistant outer cuticularized wall composed largely of sporopollenin called the exospore or exine. The exine often bears spines or warts, or is variously sculptured, which are helpful in identifying various genus, species or even sub-species.
What is diatom?
Diatom is a major group of algae belonging to class Bacillariophycaeae. The diatom cells are enclosed by cell wall made of silica, called a frustule.
These are carbonized grains / seeds collected meticulously from archaeological contexts with the aid of techniques like wet and dry sieving, floatation techniques and others. The carbonized grains come from the contexts of ancient past when they were accidentally charred or fired and thus preserved in excellent conditions.
Other categories of archaeobotanical samples are charcoal samples, both medium sized chunks and micro-charcoal ones, which are helpful in not only dating the contexts through radiocarbon methodology, but also their thin section study help in identifying the plant species.
Research at IIT Gandhinagar
The research at IIT Gandhinagar was aimed at analyzing samples from three sites, namely Karanpura (Harappan culture, district Hanumangarh, Rajasthan), Rupnagar (Harappan culture, district Rupnagar, Punjab) and Kopia (Early Historic site, district Sant Kabirnagar, Uttar Pradesh).
Phytolith analysis of samles from Karanpura, district Hanumangarh, Rajasthan
Karanpura is located on the left bank of dried river channel of River Drisadvati near the town of Bhadra in district Hanumangarh, Rajasthan (see poster). The soil samples collected from the excavation of this site during the field seasons 2012-13 and 2013-14 by Archaeological Survey of India. The samples came from two key trenches, viz., S170E40 III and S30E130 IV. Interestingly, the site did not yield any remains of charred grains / seeds and hence it was essential to study the soil samples for phytolith, pollen remains, to reconstructing the floral economy of Harappans in northern Rajasthan. Further, the study was also aimed in understanding the palaeo-climate during third millennium BCE.
The standard chemical processing procedures was carried out for phytoliths (Pearsall: 1989) with slight modifications.
The preliminary investigations from S170E40 III show variation in phytolith assemblage during early Harappan and Harappan phases. The phytolith recovery from early Harappan phase is very poor with evidence of bulliform, elongated and smoth walled ones. However, as the Harappan phase is reached, recovery of phytoliths improves gradually with few phases of decrease in the number of morphotypes.
There may be several factors influencing the causes in fluctuation of phytolith recovery during different phases in geological past. The reasons could be (i) varied flora present during the phases, (ii) local factors like human and associated imparts majorly affect any area within short span of time and (iii) nature of sediment and preservation conditions.
The studies so far indicate that the region witnessed climatic shifts during third millennium BCE, but the factors governing them could not be derived. The data also indicates that the grass flora increased during the Harappan phase also indicating aridity associated with the decrease in the rainfall.
Phytolith analysis of samples from Kopia, district Sant Kabirnagar, Uttar Pradesh
Kopia is located on the left bank and 3.5 km away from the present channel of River Ami and also close to a dry lake which is a part of an ox-bow lake known as Nandwan Tal.
The preliminary analysis of phytolith samples show presence of bulliform, cross, dumb bell shaped ones.
Further studies will help in understanding more details.
Archaeobotanical investigations from Rupnagar, district Rupnagar, Punjab
The samples investigated for this study came from the archaeological excavations carried out at Rupnagar during the field season 2011-12 by Archaeological Survey of India (see poster). Rupnagar is located on the left bank of River Satluj, where the river takes a northern turn after entering the plains leaving the Siwaliks. Rupnagar, during the earlier excavation under Y.D. Sharma brought to light a multi-cultural occupation starting from Harappan culture onwards up to medieval periods.
The excavation carried out during 2011-12 brought to light occupations of Harappan and Bara phase, followed by Painted Grey Ware culture and Early Historical period.
The charred grains collected from the Harappan as well as Historical period were investigated at IIT Gandhinagar (see poster).
The investigations consisted of preliminary sorting of grains / seeds without the aid of microscope and then the broad based identification carried out with the help of a stereomicroscope.
The preliminary analysis of grains / seeds from Harappan phase indicates the presence of seeds of wheat, rice, barley. Further, seeds of zizyphus jujuba (Ber fruit), emlica officinalis (Amla) and its wild relatives.
The preliminary analysis of grains / seeds from Historical period indicates the presence of seeds of two varieties of wheat (Triticum aestivium and T. dicoccum), rice, barley, lentils, fruit coat of zizyphus jujube (Ber fruit) and emlica officinalis (Amla)