EDMONTON — It's our world now.
International scientists, including one Canadian, say that humans have changed the Earth so much that it's time to recognize we have created a new era in the planet's history.
"The case is pretty strong," said Alex Wolfe, a University of Alberta paleobiologist and one of 24 co-authors of a paper published Thursday in the journal Science that argues for official designation of the Anthropocene Epoch.
The term Anthropocene — meaning "human period" — has been used for about 15 years whenever scientists want to talk about the cumulative impacts people have had on Earth.
Some suggest it should start with the birth of agriculture. Others argue it begins with the Industrial Revolution. And some say our impacts just don't justify a separate epoch.
Wolfe and three dozen colleagues from around the world were tasked in 2009 by an international commission to find out if the Anthropocene is real and, if so, when it started.
Yes, they say. It began July 16, 1945.
That's the date of the first nuclear test explosion in Alamogordo, N.M. It's also set off what's come to be called the Great Acceleration — the post-war explosion of energy use, resource exploitation and population growth that is now visible everywhere on the planet.
The paper says that along with radioactive traces from nuclear tests, new materials such as plastic and pure aluminum have become pervasive in the environment. Old materials such as concrete have spread wildly — over half the concrete produced since the time of the Romans comes from the last 20 years.
"Now we have rocks that are laden with microplastics and macroplastics and elevated inventories of trace elements and human waste products," Wolfe said.
More than half the Earth's surface has been modified for human use. People have dug up, tunnelled through or otherwise moved enough dirt and rock to cover the entire planet — including the oceans — with a kilogram of material for every square metre.
"Humans now move as much earth materials as the sum of volcanoes, (earthquakes) and landslides," said Wolfe.
Soot and ash, visible in sediments since the Industrial Revolution, became even more prevalent during the Acceleration. Global carbon, nitrogen and phosphorus cycles have all altered.
Extinction rates of mammals, birds, reptiles, amphibians and fish began growing in the 19th century. If current trends continue, scientists expect about three-quarters of all species to disappear over the next few centuries in "a process that is probably already underway," says the paper.
That would be the sixth great extinction since life began on Earth, akin to the disappearance of the dinosaurs.
Meanwhile, sea levels began to rise between 1905 and 1945. Climate warming has exceeded levels of natural variability. Rates of change have been increasing since 1970.
"It's an important lesson," said Wolfe. "There are a lot of people who still believe that humans don't have the power to pervasively modify the planet."
Nor are the changes likely to stop.
"It does present a challenge on a planet that's probably going to have a population of 10 billion by mid-century."
The proposal to officially declare the start of the Anthropocene goes before an international scientific panel in Oslo, Norway, in April.
— Follow Bob Weber on Twitter at @row1960