Has Earth entered the anthropocene epoch?

Death and rebirth are the bookends of time.

For over 4.5 billion years, each day on Earth has begun the same way: with the rising of the sun.

But earth scientists look for greater changes, choosing great extinctions or periods of evolution to mark the passing of one geological period into another.

Our destiny, some might argue, first began when fish climbed out of the primordial oceans and onto the shore some 400 million years ago during the Paleozoic Era.

But it was during the Holocene Epoch, after the Pleistocene Ice Ages ended, that humans turned from hunting and gathering to organizing social groups, thus forming the civilizations of the world.

Some say we are still in the Holocene. But others have begun to wonder if we may now be living in a new epoch, one defined by the environmental consequences of man.

This new time period, dubbed the anthropocene in 2000 by biologist Eugene F. Stoermer and Nobel-winning atmospheric chemist Paul Crutzen, it marks the most recent interval of geological time that is characterized by how human activities forever changed the geography and climate of the planet.

But when, exactly, was that?

If the anthropocene were to become an official epoch, it would be the first time a geological boundary could be witnessed by scientifically literate human beings.

But first, scientists must come up with a start date. Some argue it began in the Industrial Revolution, when factories caused an increase in carbon emissions. Others have said it began earlier than that, when agriculture caused widespread deforestation. Still others have argued that it began much more recently, in the second half of the 20th century.

Alex Wolfe, a professor at University of Alberta, believes that the anthropocene started during the Great Acceleration, a term used by scientists to describe rapid climate change in the last half of the 20th century.

This is when, Wolfe said, human activity did more than just impact the planet — it actually started to control it.

Wolfe is in favour of formally recognizing the Anthropocene Epoch. But in order to find an official start date for the epoch, he said, we have to find a “geological horizon.”

As part of the Anthropocene Working Group, he published a paper in the Quaternary International that argued for a distinct start date: July 16, 1945, the Trinity atomic bomb tests.

Although that date carries great weight in the pages of human history, he said it was chosen not because it’s a metaphor, but because it can be measured. The bomb and subsequent nuclear fallout has left radioactive footprints in rock formations that will serve as a marker for thousands of years.

“We’re essentially using the nuclear test as a pageholder for a series of events that represent, in our mind, a transformation of the earth system,” he said.

But William Ruddiman, a paleoclimatologist at the University of Virginia, thinks it goes back much farther than that.

“[The atom bomb] is an important marker in human history, but it’s not even close to the whole story,” he said.

In a paper published in the journal Science, Ruddiman argues that the anthropocene began thousands of years ago, when humans chopped down the forest to make way for agriculture.

“If you look out from space at the planet, the biggest change that would strike your eyes is that all these green forests have been turned into yellow meadows,” he said.

Starting the anthropocene in 1945, he said, would be like saying the Wild West was tamed when the Sears Tower was built in Chicago in 1970.

End of an epoch?

Right now, the anthropocene is an informal term used to describe a period of time when human impact on the planet became more pervasive. But in 2016, the International Commission on Stratigraphy will meet, and the Anthropocene Working Group hopes to submit a proposal in favour of making the Anthropocene Epoch an official time unit on the Geological Time Scale.

“Right now anthropocene means different things to different people,” Wolfe said, arguing that it would be more useful if everyone could agree on what it is and when it began.

“These transformations are apace, they were begun decades ago, and their fingerprint is . . . absolutely pervasive,” he said.

But Ruddiman said that while he thinks it’s a useful term, he’s against turning the “little a” into a “big-A Anthropocene.”

“There are lots of important changes that humans have made, and they come in at lots of times and lots of places,” Ruddiman said.

The current geological time period, the Holocene Epoch, has lasted for 12,000 years. If Wolfe is right, and we’re just 70 years into the Anthropocene Epoch, then we’re really just starting to see what the consequences of human activities will look like for the planet.

“It’s really just the beginning,” he said.