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Every human being leaves traces behind, and has done so for thousands of years. In a new study, a team led by lead author Dr. Yanming Ruan from MARUM—Center for Marine Environmental Sciences at the University of Bremen shows that human influence on soil erosion goes back much further than previously thought. Their findings have now been in Geophysical Research Letters.

The basis for the findings of the international team, which includes researchers from Germany, the Netherlands, and China, is a sediment core obtained in 2005 during an expedition with the research vessel SONNE in the Indian Ocean off the coast of East Java (Indonesia). Particles that are transported by rain into rivers and then into the sea accumulate on the ocean floor. These samples often contain unique information about the past that is preserved in the sediments for thousands of years.

This enabled them to demonstrate how soil erosion has changed and the reasons for this. To do this, they analyzed sediments dating back 5,000 years. For the study, the team focused on molecular markers for soil erosion and fire events and compared them with reconstructions of vegetation and hydroclimate, i.e., humidity, in this region. They divided the past 5,000 years into periods in which soil erosion changed and compared them with the other parameters to find out what the respective driving factors were.

It turned out that people in this region began cultivating the land around 3,500 years ago. Without any evidence of changing vegetation or hydroclimate, fire markers increased, indicating slash-and-burn practices to clear the land.

"Such early farming practices likely made soils more susceptible to erosion," explains lead author Yanming Ruan. This is a clear signal of human influence on nature—much earlier than researchers had previously thought.

Dr. Enno Schefuß from MARUM adds, "In order to assess the influence of humans on the climate and environment, one must compare the current situation with an uninfluenced period. Our results show that we need to look back much further. In this case, we are talking about the 'deep root of the Anthropocene,' i.e., the period in which humans had a major impact on the natural environment and climate."

According to Ruan, the data also show that permanent, more intensive agriculture has led to the most severe soil erosion in around 500 years. This has been exacerbated by intense monsoon rains. In the future, progressive global warming could lead to more frequent and heavier rainfall in Indonesia. According to the study's conclusion, this could further accelerate erosion rates in the future, posing risks to natural resources.