One word for the present: plastics

Humans have created 5 billion tonnes of plastic, a material which was virtually non-existent until the 20th century 

Historians may soon be looking back at the 20th and early 21st centuries as the time of computers and the Internet, bold ventures into space and the splitting of the atom. But what will scholars in the distant future find worthy of note? If there’s anyone around with a penchant for palaeontology hundreds of thousands of years from now, a surprise awaits in the stratigraphic layers containing the remains of our time.

Anyone digging into the earth would find a sudden, explosive increase in a new kind of material—plastic. Once underground, plastic will fossilize well, leaving a distinct signature. And there’s plenty of it. Until the 20th century, plastic was virtually non-existent. Since then, humans have created 5 billion tonnes. The palaeontologist Jan Zalasiewicz has calculated that if it were all converted into cling wrap, there would be enough to wrap the globe.

Until about 20 years ago, Zalasiewicz said, the idea that people could permanently change the planet was considered nonsense. Human beings were too puny and the planet too vast.

“The scale of geological processes such as mountain building and volcanic eruptions have been held to be much greater than anything humans can rustle up,” he said. But over the last several decades, he added, it’s become clear that human-generated effects “can be big on a geological scale and can be more or less permanent”.

Geologic maps of the future might refer to our time as the Slobocene era, or the Trashiferous period. Or maybe the name scientists recently coined—Anthropocene—will stick. It refers to the time when humankind started to make an indelible mark. Changes that characterize the Anthropocene include the widespread production of aluminum and concrete as well as plastics, and distinct changes in the chemistry of the atmosphere and oceans.

Plastics have been important for distributing clean food and water, for medical devices, surgical gloves and affordable clothing. They’ve played a big role in health and sanitation. The fact that they don’t dissolve or decay is a plus for most of their intended uses. But there are unintended consequences.

Some plastics are recycled, but most go into landfills or become litter. Recently, scientists have come to realize that much of the plastic in the environment is in the form of invisible particles. Some of these come from the breakdown of bags and other floating trash in the oceans, some from toothpaste and cosmetics, and much of it from clothes, which are mostly made from synthetic materials and give off plastic fibers every time they go through a wash. These “microplastics” can be measured in sand from beaches around the world, and in the guts of many fish.

Zalasiewicz was lead author on a recently published assessment of the very-long-term impact of plastics. It appeared in a new journal called Anthropocene. There, he and colleagues projected the likely chemical signature of the microplastics and the preserved bottles and other trash in shapes and sizes that could keep future palaeontologists scratching their heads.

A lot depends on the next few decades, he said. If plastics are produced at the current rate and there’s no increase in recycling, by 2040 there will be enough to cling wrap the earth six times.

It’s also possible that people will switch to something better than plastic. Scientists at Stanford University recently succeeded in making a renewable plastic-like material from carbon dioxide and waste plant fiber. Widespread adoption of this or something like it could radically change the view from the future.

One of the lessons in the plastic assessment was that changes made over just decades—eye blinks in geologic time —can sometimes persist for aeons. Atmospheric chemists say that the carbon dioxide that goes up this century won’t come down for tens of thousands of years. Changes in ocean chemistry and temperature could persist even longer.

Of course, even the tiny plankton that Zalasiewicz has studied can leave fossils, since they use hard materials to build protective coverings. But future palaeontologists looking back at contemporary changes to the planet would see something unusual, he said. “There’s no real precedent for them any time in geologic history.