How Analytical Chemistry Helped to Reveal Our Coal Burning Past

Title: Earliest systematic coal exploitation for fuel extended to ~3600 B.P.
Authors: Menghan Qiu, Ruiliang Liu, Xingyuan Li, Linyao Du, Qiurong Ruan, A. Mark Pollard, Shanjia Zhang, Xiao Yuan, Fengwen Liu, Gang Li, Gaojun Li, Zhimin Jiao, Jiaming Luo, Shengqian Chen, Xiaoyan Yang, Yongqiang Wang, Jianye Han, Fahu Chen, Guanghui Dong
Journal: Science Advances
Year: 2023

Despite the many environmental issues associated with the modern-day usage of coal as a fuel, the relationship between humans and this strange sediment may go back further than you think. Evidence of sporadic coal burning has been found as far back as the Late Paleolithic, but no evidence has been found of regular, systematic coal usage until much later eras. While previous estimates for the earliest systematic exploitation of coal have been attributed to the people of Classical Greece and the Chinese Warring States period, around 2400 to 2100 years ago, recent work indicates that these societies may have been late to the party.

In their recent publication, Qiu et al. outline findings concerning abundant coal remains on a site dated to around 3600 years ago. This pushes the date for the earliest systematic exploitation of coal back by about a thousand years. At the site in the region of Xinjiang, in western China, the researchers describe a settlement occupied during two distinct periods. Only a few remains were uncovered from the earlier period of around 4500 to 4300 years ago. However, extensive material was uncovered from the more recent period, 3600 to 2900 years ago. The evidence for this more recent settlement included building foundations such as a mausoleum which was noted as potentially the largest single building in prehistoric Xinjiang. The site also included numerous coal remains, including coal storage pits and burned coal in hearths.

In order to shed light on this society’s use of coal, Qui et al. wanted to identify where the discovered coal had come from. The researchers identified several sites in the region with abundant coal deposits and collected coal samples from them. The team then used several variations of an analytical technique known as inductively coupled plasma mass spectrometry (ICP-MS) to analyse the elemental composition of each coal sample. ICP-MS works by decomposing a sample to ions of its constituent elements, using an argon plasma. These elemental ions are then passed into a mass spectrometer which separates the ions by mass using an electromagnetic field. The detector in the mass spectrometer is then able to count the number of ions of each mass to give information on the elemental composition of the sample.

By comparing the elemental composition of each coal sample to the samples collected at the archaeological site, the team were able to show that coal was preferentially collected from a few of the coal deposits. This preferential harvesting, coupled with the similar distances to each of the candidate coal deposits, led the researchers to conclude that residents of this settlement consciously selected coal of a higher quality. The analysis of a selection of soil samples by x-ray fluorescence also demonstrated the presence of heavy metals associated with the smelting and working of metals. As humanity considers its current relationship with fuel and energy production, it is important to understand the role that non-renewable energy sources have had on shaping our ancestor’s societies. In their article, Qui et al. note that the two distinct periods of occupation of this site likely resulted from climatic variations resulting in cooler, less favourable conditions for settlement. These climatic changes may have, in part, spurred the second set of inhabitants to adopt coal as a primary energy source. This inverts our current situation of attempting to change our energy sources in an effort to prevent even more severe changes to global climate.

Featured Image by Pixabay from Pexels.

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