Defining—and Redefining—the Anthropocene

Quiet, small-but-deep Crawford Lake in Canada’s Niagara Escarpment in Ontario may soon become the symbolic starting point for a radical new chapter in Earth’s official history: the Anthropocene, or the Age of Humans. Scientists say that the geological indicators for this new era of human activity include high levels of ash from coal-fired power stations, high concentrations of heavy metals and the presence of plastic.

Plastic. That durable, low-cost and versatile material that also pollutes the environment and gives off toxins. No other material may be so loved by us and yet so reviled.

Now, however, a new method to convert waste plastic into fuel and raw materials promises to help close the carbon cycle at mild temperatures and with high yields. In another exciting and wild twist of science, chemists have taken the first step toward making all our plastic trash vanish.

The Crawford Lake location

Every new phase of Earth’s history begins with a “golden spike”—a spot in the geologic record where proof of a global transformation is perfectly preserved.

For example, an exposed Tunisian cliff face bearing traces of an ancient asteroid impact marks the transition from the age of the dinosaurs to the Cenozoic era. Hydrogen molecules uncovered in Greenland’s ice denote the start of the Holocene—the 11,700-year stretch of stable temperatures that encompasses all human civilization, up to the present day.

Now, researchers have selected a spot which they believe best represents the next epoch: Crawford Lake in Canada.

Locals used to say that Crawford Lake was bottomless. Anything that dropped into the basin, it seemed, would fall forever. Yet, when scientists finally investigated the lake’s murky depths, they found much more than a void. For centuries, Crawford Lake has quietly absorbed the signs of change from the surface world. Whatever fell into the water would drift down to the lake’s floor. There, it was permanently preserved in layers of mud. Digging into these sediments, scientists have uncovered a record of more than a thousand years of history. The lake shows—perhaps more than any other place on Earth—that humans have transformed the planet’s chemistry and climate at a pace never seen before. Because these changes are so fundamental, they mark a new chapter in geologic time: the Anthropocene.

Soon, researchers will determine whether Crawford Lake should be named the official starting point for this geologic chapter, with pollution-laden sediments from the 1950s marking the transition from the dependable environment of the past to the uncertain, new reality humans have created.

In just seven decades, the scientists say, humans have brought about greater changes than they did in more than seven millennia. Never in Earth’s history has the world changed this much, this fast. Never has a single species had the capacity to cause so much damage—or the ability to prevent so much harm.

In 2009, the International Commission on Stratigraphy—the scientific body responsible for defining the phases of Earth’s past—created a new working group to identify a potential golden spike site that would validate the naming of a new epoch.

Their search spanned locations from mountain summits to ocean depths, from the Antarctic ice sheet to tropical coral reefs. Samples from a range of these sites were then sent for analysis to England’s University of Southampton radioanalytical labs. Researchers there processed the samples to detect a key marker of human influence on the environment: the presence of plutonium.

In nature, plutonium exists only in trace amounts. But early in the 1950s, when the first hydrogen bomb tests took place, scientists saw an unprecedented increase and then a spike in the levels of plutonium in core samples from around the world. Then came a decline in plutonium from the mid-1960s—when the Nuclear Test Ban Treaty came into effect—and onward.

The other geological indicators of human activity (high levels of ash from coal-fired power stations, high concentrations of heavy metals—such as lead—and the presence of plastic fibers and fragments) coincide with “The Great Acceleration”—a dramatic surge across a range of human activity, from energy use to transportation, starting in the mid-20th century and continuing today.

From the hundreds of samples analyzed at the University of Southampton, a sediment core from Crawford Lake showed that no other water body possessed its particular combination of attributes, making Crawford Lake a unique bellwether of global change.

The presence of plastic

The ubiquitous presence of the Anthropocene’s plastics is now a problem. And a report from the Minderoo-Monaco Commission on Plastics and Human Health, published in the Annals of Global Health in March 2023, is being called a significant leap forward in connecting the human health implications of plastics to the health of our oceans.

Some of the commission’s key findings are:

• Plastics cause disease, impairment and premature mortality at every stage of their life cycle, with the health repercussions disproportionately affecting vulnerable, low-income, minority communities, particularly children.

• Toxic chemicals that are added to plastics and routinely detected in people are, among other effects, known to increase the risk of cancers, cardiovascular disease, miscarriages and obesity.

• Plastic waste is commonplace in the global environment, with microplastics occurring throughout the ocean and the marine food chain.

The commission concluded that current plastic production, use and disposal patterns are not sustainable and are responsible for significant harm to human health, the economy and the environment—especially the oceans—as well as for deep societal injustices. Plastics, the report notes, account for an estimated 4 to 5 percent of all greenhouse gas emissions across their life cycles, making them a large-scale contributor to climate change.

The study calculated that the cost of the health repercussions attributed to plastic production was $250 billion in a 12-month period, which is more than the gross domestic product (GDP) of New Zealand or Finland in 2015, the year the data was collected. In addition, health-care costs associated with chemicals in plastics are estimated to be in the hundreds of billions of dollars. The research also noted that the spread of fast-food and discount stores in poorer communities increased exposure to plastic packaging, products, and associated chemicals and impacts. Besides their intrinsic effects, plastics can be a vector for potentially pathogenic microorganisms and other chemicals adsorbed from polluted water.

As a result of its findings, the commission urged that a cap on global plastic production become a defining feature of the Global Plastics Treaty negotiated at the United Nations, and that its focus should go beyond marine litter to address the impacts of plastics across their entire life cycles, including the many thousands of chemicals incorporated into plastics and their human health effects.

The good news is that the commission says that many of the harms of plastics can be avoided via alternative designs, better production practices, less toxic chemicals and decreased consumption.

The breaking of bonds

There are already better production practices in the works.

A lot of potentially useful raw materials are bound up in used face masks, food wrap and grocery bags. But it has been much cheaper to keep making more of these single-use plastics than to recover and recycle them. Recently, however, an international research team led by the Department of Energy’s Pacific Northwest National Laboratory has cracked the code that stymied previous attempts to break down persistent plastics.

Typically, recycling plastics requires “cracking” or splitting apart the tough and stable bonds that make them so long-lived in the environment. This cracking step requires high temperatures, making it energy intensive and expensive. But by combining the cracking step with a second reaction step that immediately completes the conversion to a liquid, gasoline-like fuel without unwanted by-products, the team has overcome those two obstacles.

The second step deploys what are known as “alkylation catalysts.” These catalysts provide a chemical reaction currently being used by the petroleum industry to improve the octane rating of gasoline. Crucially, in the current study, the alkylation reaction immediately follows the cracking step in a single reaction vessel, near room temperature. This study demonstrates a new, practical solution for closing the carbon cycle for waste plastic that is closer to implementation than many others being proposed.

There is one limitation, however. The process works for low-density polyethylene products (LDPE, plastic resin code #4), such as plastic films and squeezable bottles; and polypropylene products (PP, plastic resin code #5) that are not typically collected in curbside recycling programs in the United States. High-density polyethylene (HPDE, plastic resin code #2) would require a pretreatment to allow the catalyst access to the bonds it needs to break.

Solving the problem of persistent waste plastic will require us to reach a critical point where it makes more sense to collect it and return it to use than to treat it as disposable. This study shows that we can make that conversion quickly and at mild conditions, providing one of the incentives needed to move forward to that tipping point.

The transformation of trash

For more good news on the plastics front, we only need to look at the chemists working at the University of Colorado Boulder. They have developed another new way to recycle a common type of plastic found in soda bottles and other packaging. The method relies on electricity and some chemical reactions, and it’s simple enough that you can watch the plastic break apart in front of your eyes.

Recycling bins might look like a good solution to the world’s plastics problem. But most municipalities around the world have struggled to collect and sort the mountains of rubbish that people produce every day. The result is that less than one-third of all PET (polyethylene terephthalate) plastic in the U.S. comes close to being recycled (other types of plastic lag even farther behind). Even then, methods like melting plastic waste or dissolving it in acid can alter the material’s properties in the process.

For example, using current methods of recycling, if you melt a plastic bottle, you can produce one disposable plastic bag that you’d have to pay money for at the grocery store. In contrast, the University of Colorado Boulder team wants to find a way to use the basic ingredients from old plastic bottles to make new plastic bottles.

In a new approach to chemical recycling, a report in the journal Chem Catalysis outlines how the researchers are one step close to recovering the molecular materials in plastics to use them again.

The University of Colorado Boulder scientists focused on PET plastics, which consumers encounter every day in blister packs, polyester fabrics and water bottles. In small-scale lab experiments, the researchers mixed bits of that plastic with a special kind of molecule; then they applied a small electric voltage. Within minutes, the PET began to disintegrate.

That feat was achieved due to a process called electrolysis, where electricity is used to break apart molecules. Chemists, for example, have long known that they can apply a voltage to beakers filled with water and salts to split those water molecules into hydrogen and oxygen gases.

But PET plastic is a lot harder to divide than water. In the new study, the scientists ground up plastic bottles, then mixed the powder into a solution. Next, they added an extra ingredient, a molecule known as [N-DMBI]+ salt, to the solution. In the presence of electricity, this molecule forms a “reactive mediator” that can donate its extra electron to the PET, causing the grains of plastic to come undone. After breaking down the PET into its basic building blocks, they can be recovered and, potentially, be used to make something new.

The team says that it has a lot more work to do before its recycling tool can take a realistic bite out of the world’s plastic trash problem. But watching plastic—which can stick around in garbage piles for centuries—disappear in a matter of hours or days was fun.

The entrance of an era

Living at a time that marks a new epoch is exciting. What’s less thrilling, however, is knowing that the beginning of the new era you happen to be here to witness is not one marked by better conditions than the previous period, but by one that could spell disaster and more hardship on Earth.

However, there is still much that we can do to redefine the Anthropocene. The plastics that characterize our present era—and, while having their downsides, have had many positive applications, for example, in construction, food storage and medicine—can be reformatted and thus rethought into a beneficial hallmark of the new age we humans are ushering in.

Here’s to hope, and to finding your true places and natural habitats,

Candy