Soil scientists at St Petersburg University reconstruct weather conditions in the North Caucasus during the Middle Palaeolithic
Scientists from St Petersburg University as part of a research team have analysed palaeosols in Adygea and determined what climatic conditions were present in this area during the last two waves of Neanderthals. It turned out that at the beginning of the Last Glacial Period, an abrupt change in bioclimatic conditions occurred in the northwestern Caucasus, causing ancient people to leave the site under environmental stress.
The Hadjoh 2 site in the Republic of Adygea is a rare open-air archaeological monument that appeared about 45,000-120,000 years ago and has survived to this day. The researchers have ascertained four periods of human occupancy at the site, two of which can be considered prolonged. These waves belong to the periods of 100,000-120,000 years ago and 45,000-60,000 years ago. Archaeologists from St Petersburg and Adygea found Stone Age tools and animal bones at the site, and sent soil samples to soil scientists from St Petersburg University for study.
The research findings are published in the Journal of Archaeological Science: Reports.
‘Archaeologists are interested in the physical traces of human activity in the past, preserved in the occupation layers. For us, soil scientists, it is interesting to study the condition of the soil, which can tell us a lot about the living conditions of the people of that era. By combining the data obtained by the archaeologists with the results of our study, we can obtain the most complete picture of human life in a particular period of time. We have analysed fragments of palaeosols selected from the Hadjoh 2 site, studied the structure and properties of the preserved horizons of their profiles, and the peculiarities of the morphological structure at different hierarchical levels, including meso- and micromorphology,’ said Aleksey Rusakov, Acting Head of the Department of Soil Science and Soil Ecology at St Petersburg University.
As Aleksey Rusakov explained, analysis of the soil structure relating to the periods of hominin occupation of the region suggests that the climate in the area has changed, and it has changed significantly. In the first wave of development of these territories (49,000 years ago) the climate was more arid, i.e. dry. Then, in the period of the second human arrival, it changed to a more humid, wetter climate.
At the same time, in the period when our ancestors left the territory and did not live there for almost 50,000 years, it was characterised by a sharp cold snap.
These data were obtained by using a set of interdisciplinary methods. The researchers used the method of morphological analysis of soil, i.e. studying its composition by layers. They also analysed physical and chemical properties, and palaeomagnetic susceptibility of soils. Additionally, they studied colour characteristics and carried out spore-pollen analysis. The method of optically stimulated luminescence was also applied to determine the time when minerals in the soil and sediments were last exposed to sunlight on the surface.
General conclusions are drawn by the scientists on the basis of full analysis of five main factors of soil formation, which were identified by the founder of soil science, graduate and professor of mineralogy and crystallography of St Petersburg University (1884-1897) Vasily Dokuchaev. These include soil-forming rock, climate, topography, organisms and time of soil functioning. From these factors, it is possible to: judge about the processes taking place in soil; and, based on these data, draw conclusions about soil properties recorded in the morphological structure of soil profiles. However, the process also works the other way round, which is what the scientists took advantage of in this case, identifying climatic features from the properties of palaeosols.
The scientists also tested the magnetic susceptibility of palaeosols. In one of the upper layers from about 50 000 years ago, they found an increase in the value of this parameter. The scientists speculate that this may be due to volcanic ash being brought in.