It is well known that the Industrial revolution led to a staggering shift in the global nitrogen cycle – a key process that supports life by circulating nutrients between the land, atmosphere, and oceans – but human-linked impacts on the environment in earlier periods of history are far less well understood. A paper recently published by an international team of researchers led by the University of British Columbia and the Institute of Technology, Sligo, is set to change that, however, showing that humans may have had a significant impact on the nitrogen cycle in Ireland during the Bronze Age.
By analysing the nitrogen isotope values in collagen preserved in 757 animal bones (some of which are pictured above), the team was able to explore variations in Ireland’s nitrogen cycle, spanning the late Pleistocene to the post-medieval period. Both wild and domestic animals were represented among the samples, which came from over 90 archaeological and palaeontological sites across the whole island. Their bones preserve evidence of the nitrogen cycle thanks to the plants that they ate.
The results demonstrate that while a small increase in nitrogen isotope values was seen between the late Pleistocene and the Neolithic period – a pattern that has been noted in other studies as occurring across Europe at this time – the most striking discovery was a fundamental shift showing increased nitrogen isotope values across Ireland during the later Bronze Age. These levels remained elevated during the Iron Age, then increased again during the early medieval period, before slightly decreasing in the later medieval/post-medieval periods.
What was driving this Bronze Age increase? The archaeological record shows that during this time there was a significant rise in deforestation, agriculture, and animal husbandry, possibly indicating that these practices may have had a profound and lasting impact on the environment. As Eric Guiry, the lead author on the paper and post-doctoral fellow at the University of British Columbia, suggests: ‘[this is] the turning point where humanity goes from being a part of the environment to being a dominant driver in key processes.’
This article appeared in CA 342.