Earth’s history: Should this phase be called the Anthropocene era?

Geologists began to consider that the Earth might be millions of years old, but it wasn’t until the 1950s that researchers established that our planet’s age is around 4.5 billion years.
Geologists began to consider that the Earth might be millions of years old, but it wasn’t until the 1950s that researchers established that our planet’s age is around 4.5 billion years.

Summary

  • We must recognize the mark left by our species on the planet. The role we have played justifies renaming the ongoing era.

One of the many things to appreciate about our home planet is that buried in its layers of rock is a kind of time machine. These strata tell us about our tumultuous history of glaciers, volcanoes and asteroid impacts, as well as the plants and animals that lived, evolved and died over aeons. There’s no doubt that future scientists will find much to study in the layer being laid down right now— weird materials from plastic to plutonium and dramatic changes in the nature of fossilized plants and animals. And yet, a group of scientists rejected a proposal to give this epoch a new name: the Anthropocene, derived from the Greek word for human. That’s too bad. It’s a fitting name but seems to have been dismissed over technicalities.

The approach of dividing deep time into segments began before we knew how old our planet was. Geologists in the late 1700s and early 1800s saw layers of rock with different materials and fossils. These sometimes changed at abrupt boundaries. They began to consider that the Earth might be millions of years old, but it wasn’t until the 1950s that researchers established that our planet’s age is around 4.5 billion years.

By the early 1800s, we had time frames. The biggest units were aeons, within which were eras, periods and epochs. Thanks to our love of dinosaur movies, some people are familiar with the Jurassic and Cretaceous periods, each spanning tens of millions of years, the latter ending with a catastrophic asteroid impact. Our current period is called the Quaternary, and within that are two epochs—the Pleistocene, which started 2.5 million years ago, and is known for periodic ice ages, and the Holocene, which started just 11,700 years ago and is known as a relatively stable and mild period that let humanity go global.

Many of the previous periods are named after geographic locations where rock formations or fossils were identified. The name Anthropocene was proposed in 2000 by chemist Paul Crutzen, who won a Nobel Prize for his part in the discovery that human activities were threatening Earth’s protective ozone layer. In 2009, a team of known as the Anthropocene Working Group set out to pick a date when the Holocene ended and the Anthropocene began. Should it start with the lead pollution of the Roman Empire, captured in ice sheets? The colonization of the Americas and Australia, which changed those continents’ biota? They settled on 1952, when humanity added plutonium and other detectable by-products of atomic bomb testing to our planet’s surface.

The recency of that date seemed to be a sticking point for the scientists who rejected the Anthropocene concept. Some also argued that what we’re calling the Anthropocene is not so much an epoch as an event—a rapid environmental change that might or might not kick off a new epoch. Some also thought it sounded too negative. Stephen Lezak, a professor at Cambridge and Oxford, argues that the name sends a pessimistic message that we’re defining the era by “human-caused environmental disaster" and that “we won’t be getting out of this mess any time soon."

But our influence doesn’t have to be seen as purely destructive. It’s downright optimistic to expect someone doing science millennia in the future looking to study what we left behind. A future scientist could be someone like Richard Alley, a professor at Penn State University and author of The Two Mile Time Machine, about drilling into Earth’s ice caps to understand the planet’s past. Alley says that since the Anthropocene just got started and represents only a sliver on the Earth’s top crust, geologists don’t need it for mapping purposes. But if you appreciate that the lines the early geologists drew through different eras represented upheavals, then what’s going on easily qualifies. “The Anthropocene very clearly is another one," he said.

Barring some spectacular technological intervention, the carbon dioxide that’s come from burning fossil fuels could take 100,000 to 500,000 years to be re-absorbed by Earth, said Alley. In the meantime, the resulting glacier loss and sea level rise will affect people for thousands of years. So however long our species lasts, the influence of recent decades will reverberate through time.

Historically, people have had trouble believing we could change something as powerful and vast as Earth’s climate. And human beings couldn’t have known, at first, that they were changing the planet’s atmosphere. Of course, we now know that humanity is leaving a big mark in the strata. What we don’t know is how future scientists will judge us. Naming this era the Anthropocene could be seen as a positive statement about our species—that we had the foresight and self-awareness to recognize our growing impact on our vast but limited Earth. ©bloomberg

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