Anthropocene: Geological evidence of human life

Geologists say the "age of humans" is here — a new epoch called the Anthropocene. Officially, we're living in an epoch known as the Holocene. But scientists say the impact of human life has been so great, despite our relatively short existence on Earth, that we should acknowledge the fact properly. 

The idea of the Anthropocene was first proposed and popularized Paul Crutzen, a Dutch meteorologist, who won the 1995 Nobel Prize in Chemistry. 

Now, scientists have found proof of the Anthropocene at Crawford Lake in Canada, according to a statement from the Max Planck Society for the Advancement of Science on Tuesday.

They say that a rock extract, or sediment core, from the lake shows a record of a "golden spike" of our human impact on planet Earth.

The spike on the sediment core was recorded in the early 1950s, a time in our recent history that saw a sharp rise in human use of fossil fuels and early fallout from nuclear and thermonuclear tests.

A collective of scientists known as the Anthropocene Working Group has proposed that this be the official marker for the start of the new epoch. 

It is the result of their 14-year hunt across 12 geological sites around the world, from Poland and Korea to Mexico and China.

They focused on two candidates: Crawford Lake and Sihailongwan Lake in northeastern China, and then took a vote.

Crawford Lake won by a vote of 60% in favor.

Crawford's evidence of the Anthropocene 

The remote lake is uniquely deep and allows for sediment to drift downwards, year upon year, with limited or no human intervention. 

It formed when a limestone cave imploded and released a flood of water. It is now about 24 meters deep, but the bottom layers of water do not mix much with the upper layers.

Every summer when the lake warms, it results in calcium carbonate precipitation. That leaves a white chalky layer, which geologists can read as a precise, annual record of the Lake Crawford environment. It's the same as the rings of a tree trunk.

Radioactive elements from nuclear testing, carbon emissions, ash and nitrogen isotopes from burning fossil fuels, the boom of purple sulfur bacteria, and atmospheric oxygen are all painted like murals on the Crawford Lake rocks.

"People can [see year-by-year] and identify what was going on or reconstruct what was going on in the atmosphere, in the water, the hydrosphere," said Francine McCarthy, a lead researcher with the Crawford Lake project.

Anthropocene evidence is a 'wake-up call'

"This should be a wake-up call for politicians," said Jürgen Renn, director of the Max Planck Institute for the History of Science.

No matter which mode of energy humans adopt in the future, Renn said, we are going to see its effect on the rocks: "There's no going back to the Holocene!"

But critics say this perspective of the Anthropocene highlights a very narrow range of human impact on the planet.

In a paper called "Three Flaws in Defining a Formal Anthropocene," geologist William Ruddiman writes that major human alterations of Earth long preceded the 1900s.

Others, such as Heather Davis, an academic in culture and media, and Zoe Todd, an assistant professor in chemistry and astronomy, have argued that the current thinking excludes the knowledge and experiences of indigenous communities.

But Colin Waters, a professor of geography at the University of Leicester and chair of the Anthropocene Working Group, has defended the group's decision.

Waters said the first global change was observed in the mid-20th century. "The sediments just don't show any significant effect from the industrial revolution," and that "if you're based in large parts of Asia, Australia, the Southern Hemisphere, there [are] no effects."

What is an epoch, anyway?

An epoch is marked by the beginning of an extended period in history. Researchers have described more than three dozen geological epochs since the early days of Earth's formation.

The Holocene, which is still our "official" epoch, has lasted 11,700 years so far. The one before that, the Pleistocene, lasted over 2 million years.

But there are larger divisions of geological time. Whether we call this the Holocene or the Anthropocene, it sits in the Neogene Period. The Neogene Period is itself only one part of the Cenozoic Era. And the Cenozoic Era belongs to the larger Phanerozoic Eon.

The Phanerozoic Eon stretches from 542 million years ago to the present. So, given that human evolution is a matter of single-digit millions of years — we only started to walk on two legs about two million years ago — we really have only walked the Earth for a blip in time.

And there is a consensus on at least one thing: If all humans were removed from the planet today, it would take centuries to reverse the impact of our carbon emissions or that of a nuclear war. That's a basic fact of our epoch, no matter the name, and that's what scientists want all of humanity to understand.

Edited by: Zulfikar Abbany