Discovery of a New Rock Type Originating from the Old Slug Heap

Nearly two decades ago, New Scientist conducted a thought experiment titled “Imagine Earth Without People,” projecting how our planet would evolve over millennia in the absence of humanity. This intriguing exploration highlighted the environmental impacts of our species without relying on speculative dread. The takeaway was clear: while it would take considerable time, nature would eventually reclaim its landscapes, leaving scant evidence of our existence. “What’s humbling and paradoxical is that Earth forgets us so swiftly,” the piece concluded.

This reflection resurfaced when I encountered a recent research article in Geology, where researchers from the University of Glasgow unveiled a geological process indicating that the Earth may never truly forget us.

The team investigated the geology of Derwent Howe along the coast of Cumbria, England, a site that served as a major iron and steel hub for about 125 years from the 1850s. This location generated massive amounts of industrial waste known as slag, with approximately 27 million cubic meters deposited along a two-kilometer stretch of coastline. While the slag heaps persist, they are steadily eroded by oceanic forces.

During their fieldwork, researchers discovered outcrops comprised of unusual sedimentary rock types. Formerly sandy shores had their geology altered quite recently, clearly indicating detrital formations made of fragments from other rocks and minerals. A closer examination revealed that this material was derived from the slag heaps, suggesting a cycle where the slag erodes, enters the ocean, and rapidly solidifies into rocks onshore.

Remarkably, this process occurs much faster than typical rock formation, which usually spans thousands or millions of years. Here, however, it seems to transpire in mere decades.

Even more astonishingly, the researchers uncovered two artifacts embedded in this rapid rock formation. One was a penny minted in 1934, and the other was a pull tab from an aluminum beverage can, less than 36 years old. This suggests that calcification can happen in mere decades, leading the team to propose a new geological process termed the “anthropomorphized rock cycle.”

“What’s remarkable is we’ve found that human-made materials can integrate into natural systems and dissolve over decades,” explained Amanda Owen, the team leader, to the University of Glasgow news team. “This challenges our understanding of rock formation and implies that the waste created during the modern era will have a lasting impact on our future.”

Much like with Derwent Howe, this phenomenon extends worldwide. A similar rock was discovered near Bilbao, Spain in 2022, though dating it proved challenging. David Brown, a team member, noted that slag waste presents a worldwide occurrence that will turn into rocks wherever it interacts with ocean waves.

At first glance, this might seem problematic. The environmental implications of such processes remain ambiguous. However, this discovery could indeed have a silver lining. If industrial waste solidifies into rock formations, that may offer a neat, albeit indirect, way to manage it. Rocks from Derwent Howe also revealed remnants of clothing, plastics, car tires, and fiberglass. Perhaps this process could serve as a rapid disposal method for our discarded remnants.

The study yields varied conclusions. For years, Earth scientists have debated the designation of a new geological epoch called the Anthropocene, to acknowledge that humanity has superseded natural processes as the primary influence on Earth’s systems. I’m a strong advocate for this designation, as it underscores the myriad perturbations in natural processes that have kept our planet habitable for millennia. Yet, last year, the International Geological Union opted not to endorse the Anthropocene due to controversy regarding its inception.

Now more than ever seems the right moment to reconsider that decision. Our impact on Earth’s surface marks the beginning of a new geological chapter that commenced roughly 175 years ago, observable by future civilizations. If this isn’t a new geological era, then what is?

Graham’s Week

What I’m reading

I’m listening to an anthology of comedic poems by Tim Key on audiobook.

What I’m watching

Wimbledon, the Women’s Euro, and later this month, the British and Irish Lions Rugby Test Series against Australia.

What I’m working on

I’m tending to my vegetable garden. As a beginner, I’m learning from my mistakes. How can you tell when beetroots are ready to be harvested?

Graham Lawton is a staff writer for New Scientist and the author of Must Not Grumble: The Surprising Science of Everyday Ailments. You can follow him @grahamlawton