A dark new chapter in the Earth's geological history began when the first atomic bomb was detonated on July 16 1945, an international team of scientists has proposed.
Known as the "Anthropocene", it marks the point in time when humans really began to change their planet - and not for the better.
The epoch, still in its infancy, will in centuries to come be recognised by what experts call a "Great Acceleration" of population, carbon emissions, extinctions, and environmental upheaval both on land and in the oceans.
Dutch atmospheric chemist and Nobel laureate Professor Paul Crutzen first came up with the idea of the Anthropocene 15 years ago.
Since then many academics have embraced the concept, but there has been no agreement about when the epoch began.
Now an international working group taking on the task of analysing the Anthropocene has concluded that the defining moment was the day that saw the dawn of the nuclear age.
On July 16, 1945, the first atomic bomb was detonated in the New Mexico desert 120 miles south of Santa Fe in the US.
The blast produced a searing flash and a mushroom cloud that rose 40,000 feet into the air, images of which have burned themselves into the consciousness of the human race.
The bomb, created by scientists working on the Manhattan Project, generated the destructive power of 15,000 to 20,000 tons of TNT.
It also scattered radioactive particles from the poles to the equator, leaving an indelible signal in the surface strata of the Earth.
Dr Jan Zalasiewicz, from the University of Leicester's Department of Geology, who chaired the 26-member working group, said:
"Like any geological boundary, it is not a perfect marker - levels of global radiation really rose in the early 1950s, as salvoes of bomb tests took place.
"But it may be the optimal way to resolve the multiple lines of evidence on human-driven planetary change. Time, and much more discussion, will tell."
This year the Anthropocene Working Group will put piece together more evidence on the new epoch, and also discuss other possible time boundaries.
In 2016 the group plans to make recommendations on how the new time period should be formalised, defined and characterised.
Officially the Earth is still in the Holocene (Greek for "entirely recent") epoch that began at the end of the Pleistocene 11,700 years ago.
Alternative suggestions for the start of the Anthropocene include the dawn of agriculture 12,000 years ago and the Industrial Revolution.
A research paper on the Anthropocene from the working group appears in the journal Quaternary International.