When Did the Anthropocene Really Begin?

Humans are everywhere. It’s hard to go anywhere without running into one. Even if you manage to get out of the hustle and bustle of the city and escape into nature, there’s always evidence that someone has been mucking about.

Our influence can be felt all around the planet — from the deepest oceans to the tippy-top of our atmosphere. We’ve even got some junk that’ll be floating around in space for a very long time.

But is the extent of our influence so comprehensive, so powerful, that it warrants a new geologic age? Does this mean we are in the age of humans?

The answer might lie inside of the loneliest tree in the world.

On a tiny island a few hundred miles south of New Zealand, there’s a tree that shouldn’t be there. It’s the only tree for hundreds of miles. It’s a Sitka Spruce and it’s indigenous to North America. But here it is. Thousands of miles away in the southern hemisphere. This has earned it the nickname “Loneliest Tree in the World.” Someone planted it there decades ago. Without humans, it wouldn’t be there. So its very presence on this remote island is evidence of human muckery.

And it might mark the beginning of the age of humans.

Scientists divide the Earth’s history into several geologic time periods. The age of dinosaurs was during the Mesozoic Era (widely considered the best era) which ended with an asteroid impact. Humans appeared during the Pleistocene Epoch which ended when the continental ice sheets receded. Ever since then we’ve been in the Holocene.

But now we’re probably in the Anthropocene — the age of humans.

But for the Anthropocene to be a truly scientific and official geologic time period, there has to be scientific evidence of some kind of geologic change visible in the fossil record. That means a geologist millions of years from now must be able to dig into the ground and see our presence on the Earth in the rocks somehow.

Now it’s easy to see the effect humans have on the planet. We have reshaped the landscape through agriculture and urbanization at least as much as an ice sheet. We’re changing the climate on a global scale just as much as an asteroid impact might.

But if we put ourselves in the boots of this far future geologist, when would the rocks say the Anthropocene began?

Maybe we’d see the beginning as a sudden change in ecosystems and biodiversity 11,000 years ago. This would be when humans began domesticating livestock and growing crops. We built the first cities and our influence on local ecosystems became large enough to be seen in the fossil record.

Or maybe we’d see a spike in lead and sulfate levels, and CO2 concentrations in the atmosphere about 150–200 years ago. This would correspond with the beginning of the Industrial Revolution. All of these atmospheric changes should be readily visible in the rocks or trapped in ice cores.

But both the agricultural and industrial revolutions didn’t hit the world uniformly. Agriculture began in small corners of the world and didn’t become widespread for a millenia or two. The full force of climate change and pollution didn’t begin to affect the entire planet until a century or so after the advent of the Industrial Revolution. And the greatest effects of climate change might still be in the future.

But if we moved up a little higher in the rock strata, we would see another more obvious and deadly marker of our influence. Strange artificial radionuclides would stick out of the rock like radioactive beacons. Carbon-14 and plutonium-239 would show up in our trowels in trace amounts. And their presence would coincide with all the thermonuclear bomb tests in the mid 20th century.

Geologists have yet to agree upon the beginning of the Anthropocene. But the development and testing of nuclear weapons is a popular choice. And the loneliest tree in the world might play a part in that.

Even though most of the nuclear tests took place in the northern hemisphere, the radionuclides these explosions released were scattered all over the planet, reaching as far as the loneliest tree in the world. If you looked in the bark of that tree, you would find some of these radionuclides. If our far future geologist somehow found a petrified fossil of the loneliest tree in the world, they too would find those radionuclides embedded in the fossilized tree. And these radionuclides can be found in all the plants on the island, because they’re in the soil. Like the humans who created them, they’re everywhere.

Carbon-14 has a half life of 6,000 years. It’s the isotope we measure when we want to radiocarbon date a mummy or a mammoth fossil. So carbon-14 will be detectable for tens of thousands of years.

Plutonium-239 has a half life of over 24,000 years. That means pretty much any geologist digging in the ground anywhere on the planet would find these radioactive markers of our presence far into the future.

Our influence on this planet has reached the level of asteroid impacts and ice ages. But the fact of the matter is: we are not an asteroid or an ice sheet. We are humans. The problems we face today might seem insurmountable but one good thing about acting like a geologic force is that we have geologic timescales on our side. It took 11,000 years to get where we are today. It won’t take nearly as long to fix our mistakes.

Each step in the right direction — whether that’s reducing greenhouse gases or moving to more sustainable environmental practices or just cutting down on our use of plastics — each little behavior modification compounds upon the next until the impact of our presence is moderated. The entire glacier of human influence slowly, inexorably recedes to more manageable levels.

Just because the start of the Anthropocene is written in stone doesn’t mean our future has to be.

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