Humanity's Trash Is Turning To Rock

Forbes

30-05-2025

Human garbage
Researchers from the University of Glasgow have found that trash and slag, an industrial waste product produced by the glass and steel industry, is turning into solid rock in as little as 35 years.
In a new study, the researchers have documented for the first time a new "rapid anthropoclastic rock cycle," which mimics natural rock cycles but involves human material over accelerated timescales.
It all started when one of the authors came across an aluminum tab found encased in a strange rock along the coast of Derwent Howe in West Cumbria.
Derwent Howe was home to iron and steel-making foundries during the 19th and 20th centuries, and its coast accumulated an estimated 27 million cubic-meters of furnace slag over the course of its industrial history.
The slag deposits have formed cliffs of waste material that are being eroded by coastal waves and tides forming sedimentary rocks — resembling the natural rock cycle.
A chemical analysis shows that the slag contains calcium, iron, magnesium and manganese. These elements are highly chemically reactive, which is key to causing the accelerated process of rock formation.
When the slag is eroded by the sea, it exposes the material to seawater and air, which interacts with the slag's reactive elements to create natural cements including calcite, goethite, and brucite. These cements are the same materials that bind together natural sedimentary rocks, but the chemical reactions cause the process to happen much faster.
'For a couple of hundred years, we've understood the rock cycle as a natural process that takes thousands to millions of years,' explains corresponding author Dr. Amanda Owen of the University of Glasgow's School of Geographical and Earth Sciences.
As the eroded slag is deposited and cemented, it incorporates trash carried by waves and currents to the coast.
"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. 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."
Almost like real fossils, this trash can be used to date the new 'anthropoclastic rock."
"We were able to date this process with remarkable precision," says Dr. John MacDonald, a co-author of the study. 'We found both a King George V coin from 1934 and an aluminum can tab with a design that we realized couldn't have been manufactured before 1989 embedded in the material. This gives us a maximum timeframe of 35 years for this rock formation, well within the course of a single human lifetime."
Plastiglomerates, a sort of rock resulting from marine plastic pollution, were described for the first time in 2014 from a beach on the Big Island of Hawaii. Since then similar deposits were found along the shores of the Portuguese island of Madeira, the island of Giglio in the Tyrrhenian Sea and in Cornwall in southwest Britain. As plastic pollution is nowadays widespread, likely also plastiglomerates will become more common.
'I think it's very likely that this same phenomenon is happening at any similar slag deposit along a relatively exposed coastline with some wave action anywhere in the world,' explains Dr. David Brown, the paper's third author.
The study,"Evidence for a rapid anthropoclastic rock cycle," was published in the journal Geology.
Additional material and interviews provided by the University of Glasgow.