What is the Anthropocene?

About 12,000 years ago, the end of the ice age ushered in a new geological age known as the Holocene. Its relatively warm and stable climate allowed human society to flourish.

The Holocene fostered the birth of agriculture, and the rise and fall of all major civilizations, culture and technological developments. At the same time, as humans ascended through activities like farming, they altered their environment in a way no other species had .

But many scientists have agreed the turn of this century marked the last moments of the Holocene. They say since the end of World War II, humans have transformed Earth's geology, landscape, oceans and ecosystems so profoundly and rapidly, that it has resulted in the dawning of a new geological epoch: The Anthropocene.

Anthropocene or not?

Other experts have questioned this assertion. Scientists banded under the Anthropocene Working Group (AWG) tried for over a decade to have the new epoch formalized by an independent committee of experts from the International Union of Geological Sciences.

But a "large majority" of the committee of around 24 voted down down a proposal to confirm that the Anthropocene began around 1950, according to reporting from The New York Times on March 5. The proposal cannot be heard again for a decade.

Some proponents of naming a new epoch suggest the Industrial Revolution, when humans started burning fossil fuels and emitting greenhouse gases such as carbon dioxide, marked the Anthropocene's beginnings.

Others argue it started in the 1950s when humanity's impact on the planet began to surge. Atmospheric nuclear tests in the 1950s and 1960s, for instance, spread a layer of plutonium isotopes causing a spike in sediments — a unique radiological marker left by humankind.

What is a geological epoch?

Earth's history is divided into chunks known as the geologic time scale, which is recorded in the planet's crust.

Geological epochs, such as the Late Cretaceous, the Middle Jurassic and the Holocene, typically last several million years. They each leave significant markers in rock layers, including mineral composition and fossils, reflecting major climatic changes.

Proponents of declaring a new Anthropocene epoch say human-made climate change, pollution, nuclear testing, and industrial agriculture are each leaving geological traces that will last millions of years.

Anthropocene comes from the Greek terms for human (anthropo) and recent (cene) and was made popular in 2000 by Dutch atmospheric chemist Paul J Crutzen and US biologist Eugene Stoermer when they penned a short article on the concept.

What marks have humans left?

The last time so much CO2 was in the atmosphere was 3 million years ago. High CO2 concentrations are causing planetary heating and ocean acidification — the oceans haven't been this acidic in millions of years. Industrial agriculture and urbanization have transformed landscapes and fertilizer has boosted nitrogen rates in soil and water.

The proliferation of plastics and other new materials such as concrete has left a new layer of what scientists dubbed "technofossils." Even the bones of broiler chickens, whose production for food soared around the time of World War II are another possible indication of the Anthropocene.

Meanwhile, the planet is likely going through the sixth mass extinction thanks in part to land-use and climate change. The last mass extinction happened about 65 million years ago.

Why does it matter?

Previous epochs have been triggered by events such as meteor strikes, continental movement and volcanic activity that spewed massive amounts of CO2 into the atmosphere, each leaving unique markers and altering the course of life on the planet. But this would be the first triggered by a single species.

Though the proposal to formalize the Anthropocene was voted down, the term is already used by scientists who find it a helpful concept to explain the environmental threats induced by humanity.

More than a geological term, it's become a label that communicates the profound influence humans have on the Earth, its ecosystems and other species living on the planet — and that humanity has the power to make that impact a more positive one.

Since the 1500s, science has moved away from putting humanity at the center of the universe. Nicolaus Copernicus' discovery that the Earth orbits the sun, and Charles Darwin's theory of evolution showed humans have no special place.

This new definition places humanity back in a position of self-determination, but places a new responsibility on the human species, according to philosophers.

Edited by: Jennifer Collins