The geological processes that create rocks usually take place over thousands if not millions of years. With the help of a coin and a soda can tab, researchers have identified rocks in England that formed in less than four decades. Perhaps unsurprisingly, the cause is human activity.
Researchers from the University of Glasgow’s School of Geographical and Earth Sciences discovered that slag (a waste product of the steel industry) formed a new type of rock in West Cumbria in 35 years—at most. As detailed in a study published April 10 in the journal Geology, the researchers claim to be the first to fully document and date a complete “rapid anthropoclastic rock cycle” on land: a significantly accelerated rock cycle that incorporates human-made materials. They suggest that this phenomenon is likely harming ecosystems and biodiversity at similar industrial waste locations around the world.
“When waste material is first deposited, it’s loose and can be moved around as required. What our finding shows is that we don’t have as much time as we thought to find somewhere to put it where it will have minimal impact on the environment–instead, we may have a matter of just decades before it turns into rock, which is much more difficult to manage,” co-author Amanda Owen said in a university statement.
During the 19th and 20th centuries, Derwent Howe in West Cumbria hosted heavy iron and steel industries. The 953 million cubic feet (27 million cubic meters) of slag generated by the factories turned into cliffs along the coastline, where strange formations along the human-made cliffs caught Owen and her colleagues’ attention, according to the statement.
By analyzing 13 sites along the coast, the researchers concluded that Derwent Howe’s slag contains deposits of calcium, magnesium, iron, and manganese. When exposed to seawater and air through coastal erosion, these reactive elements create natural cements such as brucite, calcite, and goethite—the same ones that bind natural sedimentary rocks together over thousands to millions of years.
“What’s remarkable here is that we’ve found these human-made materials being incorporated into natural systems and becoming lithified–essentially turning into rock–over the course of decades instead,” Owen explained. “It challenges our understanding of how a rock is formed, and suggests that the waste material we’ve produced in creating the modern world is going to have an irreversible impact on our future.”
Modern objects stuck in the lithified slag, such as a King George V coin from 1934 and an aluminum can tab from no earlier than 1989, substantiated the team’s dating of the material. Because slag clearly has all the necessary ingredients to create rocks in the presence of seawater and air, co-author David Brown suggested that the same process is likely happening at similar coastal slag deposits around the world.
Whether it’s in England or elsewhere, “that rapid appearance of rock could fundamentally affect the ecosystems above and below the water, as well as change the way that coastlines respond to the challenges of rising sea levels and more extreme weather as our planet warms,” Owen warned. “Currently, none of this is accounted for in our models of erosion of land management, which are key to helping us try to adapt to climate change.”
Moving forward, the team hopes to continue investigating this new Earth system cycle by analyzing other slag deposits. Ultimately, the study suggests that humans aren’t just driving global warming—we’re also accelerating the ancient geological processes unfolding beneath our very feet.
