Our impact on the planet Earth is so substantial now that people are demanding its own new geological epoch - known as the Anthropocene (from anthropo, for “man,” and cene, for “new” coined by Paul Crutzen and Eugene Stoermer in 2000 - means simply 'the new age of man'). While the beginning of this new era has been heatedly debated, one group of scientists now believes it has finally pinpointed the exact date of when humans began to dominate the Earth.

Humans are leaving a telltale residue on Earth. How? Scientists find a layer of plastics, radiation and soot embedded in the planet's surface, defining a new Anthropocene epoch (5). The present geologic epoch is known as the Holocene, or "entirely recent," stretching back 11,700 years before 1950 to when the last ice age began to melt and raised sea levels by roughly 120 meters over a few millennia. During that transition, carbon dioxide levels in the atmosphere increased by roughly one part per million per century. More recently, however, Co2  levels have been increasing by two ppm per year, and rather than slowly returning to an ice age the world has become ever warmer, melting more ice. The rapid increase in excess CO2 comes from the fossil fuel burning and land use of one species that first appeared approximately 200,000 years ago: Homo sapiens.

With an unusual drop in atmospheric carbon dioxide and the irreversible exchange of species between the New and Old Worlds, the human-dominated geological epoch known as the Anthropocene probably began around in 1610, a research paper claims.

Previously it has been argued that the Anthropocene, or age of humans, actually began, ranging from the start of agriculture thousands of years ago to the Industrial Revolution - or possibly its beginning hasn't even arrived yet, with the greatest human-made changes yet to come. Another strong contender was July 16, 1945 - the dawn of the nuclear era.

However, researchers from the University College London (UCL) suggest that 1610 is the rightful start of the Anthropocene.

But how do we know that humans are actually a strong enough force to push the Earth into a new epoch - one that will supposedly last for millions of years? Previous epochs began and ended due to drastic phenomena such as meteorite strikes, sustained volcanic eruptions and the shifting of the continents. But the collision of the New and Old Worlds was just as cataclysmic, according to the researchers.

When Europeans arrived in the Americas in 1492, subsequent global trade moved species to new continents and oceans, resulting in a global re-ordering of life on Earth. For example, maize, a Latin American species, first showed up in Europe in 1600 and became more abundant there in later centuries. Such long-term changes satisfy one criterion of what makes a new epoch.

In addition, the team found a "golden spike" that can be dated to the same time - that is, a natural marker of when a global environmental change occurred. That marker is a pronounced dip in atmospheric CO2 in 1610, as evidenced by Antarctic ice-core records, and is a direct result of the arrival of Europeans in the Americas.
"In a hundred thousand years scientists will look at the environmental record and know something remarkable happened in the second half of the second millennium. They will be in no doubt that these global changes to Earth were caused by their own species. Today we can say when those changes began and why. The Anthropocene probably began when species jumped continents, starting when the Old World met the New. We humans are now a geological power in our own right - as Earth-changing as a meteorite strike," according to lead author of a paper published in Nature(2), Dr. Simon Lewis (1).
So what specifically caused this Earth-altering dip in CO2? According to Lewis and his colleagues, when Europeans colonized the New World, they killed about 50 million indigenous people by spreading disease such as smallpox. This meant that just within a few decades - an extremely short period of time - farming across the continent stopped and forests were able to re-grow, removing enough CO2 from the air to produce a dramatic drop.

Co-author of the papaer, geologist Professor Mark Maslin (UCL Geography) says: “A more wide-spread recognition that human actions are driving far-reaching changes to the life-supporting infrastructure of Earth will have implications for our philosophical, social, economic and political views of our environment. But we should not despair, because the power that humans wield is unlike any other force of nature, it is reflexive and therefore can be used, withdrawn or modified. The first stage of solving our damaging relationship with our environment is recognising it.”

However, many stratigraphers (scientists who study rock layers) criticize the idea, saying clear-cut evidence for a new epoch simply isn’t there. “When you start naming geologic-time terms, you need to define what exactly the boundary is, where it appears in the rock strata .

The 'Anthropocene' is not a formally defined geological unit within the Geological Time Scale. A proposal to formalise the 'Anthropocene' is being developed by the 'Anthropocene' Working Group for consideration by the International Commission on Stratigraphy, with a current target date of 2016 (4).

However,  according to some scientists, rapid development of technology, swelling population and growing consumption of resources from crops to metals have expanded humanity's impacts, particularly after 1950 or so, an inflection point some have dubbed the "Great Acceleration." People have created long-lasting new materials, ranging from copper alloys to plastics that will form long-lived, so-called "technofossils." Enough concrete has been made by now to cover every square meter of the world in a kilogram of the building material. Sufficient plastic is currently manufactured each year to weigh as much as all seven billion–plus humans on the planet. People move nearly three times as much rock and dirt via mining than the amount that travels with water through all the world's rivers. Modern chemistry has even liberated civilization from the natural nitrogen cycle that has prevailed for the last 2.5 billion years. And tiny soot particles left over after burning coal, oil and natural gas now can be found in sediments from tropical lakes to the middle of the Pacific Ocean, a permanent smudge on the geologic record. As a result, the scientists argue, Earth has entered a new epoch that is "functionally and stratigraphically distinct from the Holocene. Moreover, humanity has even reconfigured the course of future evolution by shifting plants and animals around the globe or eliminating certain species—the same biological markers known as index fossils and used to define most of the time intervals that divide the last 540 million years, an eon known as the Phanerozoic.

The final decision on this will be made then (3) by this Anthropocene Working Group   -   a group of experts from around the world, who are tasked with determining whether the term -Anthropocene is "(a) scientifically justified (i.e. the 'geological signal' in rock strata must be sufficiently widespread, clear and distinctive) and (b) useful as a formal term to the scientific community."

References:
1. https://www.ucl.ac.uk/news/news-articles/0315/11032015-defining-ant...
2. http://www.nature.com/nature/journal/v519/n7542/full/nature14258.html

3. http://www.smithsonianmag.com/science-nature/what-is-the-anthropoce...

4. http://quaternary.stratigraphy.org/workinggroups/anthropocene/

5. http://www.sciencemag.org/content/351/6269/aad2622