When Did the Human Epoch Begin?

It’s no secret that humans, in the short amount of time they’ve existed – a little less than 300,000 years in their present form, have had a sizable impact on the planet – well before the age of climate change widely believed to have begun with the Industrial Revolution. While the last two centuries have seen the human race advance to the point of being able to alter climates – processes that typically take thousands of years. For better or worse, we’ve influenced the evolution of countless species throughout the animal kingdom – from bacteria to mammals. We’ve championed vermin like the brown rat and cockroach, and driven countless other species of plants and animals to extinction.

So greatly have we changed the planet in our conquest, that now geologists have sought to label the age in which we live as the Anthropocene. The only point of controversy, however, is deciding when exactly the Anthropocene Era began. Was it with the Industrial Revolution – or did it happen much later – with the advent of nuclear weapons in the mid-20th century? Now, there is evidence to suspect that the roots run much deeper. Many now believe that the Age of Imperialism, the first permanent settlements in North and South America by Europeans, may have ushered in this new era, leaving a substantial impact on the planet that had never been seen before. The research was published in Nature this week.

When analyzing layers of rock, geologists use these layers as a chronology for our planet. Typically, these layers represent periods of millions of years, separated by specific instances of disaster that lie in the narrative of the rock – extreme episodes of volcanic eruptions, or meteor collisions that set forth extinction events – the most known being perhaps the Cretaceous-Paleocene event that happened 65 million years ago, when an asteroid near the Yucatan Peninsula wiped out the dinosaurs.

Currently, in geologist terms, we live in the Holocene Epoch – one that began some 12,000 years ago at the end of the last Ice Age, when sea levels began to rise. However, the overwhelming evidence of climate change – even some dating well before the Industrial Revolution – to Spanish conquistadors mining silver in Peru at the turn of the 17th century – has led many geologists to label the next era as one distinct from the Holocene, in which people have greatly altered the planet from the days when we were mere hunter-gatherers. All that’s left before an international committee of geologists weighs in on the decision, is to determine which event ushered in this new era.

According to Prof. Mark Maslin, from University College London, who co-wrote the paper: “We look for these golden spikes – a real point in time when you can show in a record when the whole Earth has changed. If you look back through the entire, wonderful geological timescale, we have defined almost every boundary in that way.”

Maslin and colleagues have pinpointed the start of the Anthropocene to 1610, when such a golden spike did occur. It was just over a century since the first Europeans arrived, only three years after the establishment of the Jamestown colony in present day Virginia.

Co-author Dr Simon Lewis, also of UCL, added: “The rapid global trade after that time moved species around.

“Maize from Central America was grown in southern Europe and Africa and China. Potatoes from South America were grown in the UK, and all the way through Europe to China. Species went the other way: wheat came to North America and sugar came to South America – a real mixing of species around the world.

“We saw these species jump continents, which is a geologically unprecedented impact, setting Earth off on a new evolutionary trajectory.”

The researchers discovered ancient pollen in sediments on American soil, which show evidence of when new crops were introduced. But that’s far from the entire record. Another golden spike is in the remnants of deadly epidemics, such as smallpox, carried from European ships into the New World.

“Around 50 million people (in the Americas) died, and most of those people were farmers,” Dr. Lewis said on the BBC World Service’s Science in Action news program.

“And this farmland grew back to the original vegetation – tropical forest, dry forest or savannah. And about half the dry weight of a tree is carbon, so all that growing vegetation removed enough carbon from the atmosphere to see a pronounced dip in the global atmospheric carbon dioxide concentration that can be seen in ice core records.

“It provides an exact marker of the Anthropocene at 1610, the lowest point of CO2 in the ice-core record at that time.”

Yet, the debate is still far from over. Atomic bomb weapons testing following the Second World War has also left a pretty clear mark that humanity was here. Alternatively, Lewis and Maslin have proposed the year 1964 as the start of the Anthropocene, the year in which nuclear testing was banned across the globe. While these tests took place, however, there was a sharp buildup in radioactive carbon throughout the atmosphere. A sharp drop followed once they stopped.

Although this was a pronounced signal, this radioactivity did not lead directly to any global changes at the time.

Maslin attributes the extreme changes since then to modernization and a sharp increase in population: “In the mid-1960s, there is a huge change in everything around the planet, which is called the ‘great acceleration’ – with the population increasing by 2% per year, unprecedented changes in agriculture and food production – but the marker doesn’t link to that in any shape or form.”

Dr. Jan Zalasiewicz, from the University of Leicester, who chairs the Anthropocene Working Group and was not involved in the new study, said that this new paper offered “intriguing ideas” about where the researchers should begin to look when it comes to labeling the Anthropocene Era.

“The working group will certainly be discussing them,” he said to BBC News.

“It adds positively to the overall debate on the Anthropocene, and to the growing number of suggestions about where it should start.

“The 1610 suggestion clearly reflects a historically important event, though it would need more evidence, I think, whether the criteria they suggest would work better than the multiple signals now known to be associated with the mid-20th century ‘great acceleration’.”

Wherever the mark may begin, the golden spikes are clearly in place – imminent that there is a geological record of humanity’s interaction with the Earth, yet another attribute that may set us apart from the species that preceded us.