Michael: You and I may soon be living in a whole new era! Or at least... a whole new epoch. That’s because some scientists are thinking about changing the system we use to describe the history of Earth. The system is the Geologic Time Scale, and it’s kind of like a 4 billion-year-long calendar. But instead of being divided into months, weeks, and days, it’s separated into eons, eras, periods, epochs, and ages, based on major environmental changes that have altered the geological record forever.

For instance, the geological epoch that we’re currently in is called the Holocene, and it spans the past 11,700 years. Why that exact number? Because the Holocene is defined as having begun when the last major Ice Age ended. And the Ice Age was part of its own geological epoch, known as the Pleistocene. So, for a span of time to be considered an epoch, things have to change a lot, and in a way that can be seen in Earth’s rock layers. And according to a report released last week by a team of geologists, it may be time to recognize that humans have had exactly this kind of permanent impact on the geological record.

These scientists want to add a new chapter to the book of Earth’s history, and start referring to the time since the mid-20th century as the Anthropocene Epoch. To make their case, they list the many ways in which humans have left a mark on the planet -- changes so obvious that geologists even millions of years from now won’t be able to miss them.

Human Impact Number One on their list? Nuclear weapons. Every time a nuclear weapon goes off - which happens more often than you think - it spreads radionuclides. These are radioactive isotopes, atoms with an unusually high amount of nuclear energy. Some of these atoms occur naturally -- like in radon gas -- but many others don’t. And after 70 years of setting off nuclear bombs, we’ve left a fine dusting of synthetic isotopes, like Plutonium 239, all over the planet.

Another proposed sign of the Anthropocene times? Fossil fuels. The emissions released by burning fuels like coal and oil are doing a lot of things to the environment... most of them are not great. What interests geologists, though, are the concentrations of carbon that these fuels are creating. Burning coal and oil pumps out tons of CO2, as you know, but it also causes a decrease of certain carbon isotopes, like Carbon-13. So while higher concentrations of CO2 are being trapped in things like Antarctic ice, the changing ratios of isotopes will be detectable in fossilized trees, bones and shells far into the future.

New materials have also made a permanent impact on Earth’s environment, so they’re another major argument for the Anthropocene Epoch. Pure elemental aluminum, for example, doesn’t occur in nature, but we’ve now produced around 500 million tons of the stuff. And it can be found sprinkled all over the world, wherever forks and knives are used. Even bigger: concrete. We’ve made about 25 billion tons of concrete just over the past 20 years. And throughout human history, we’ve produced enough to cover every square meter of Earth’s surface. And of course, plastics aren’t going anywhere. Or if they are, they’re going very slowly. We make about 500 million tons of plastic a year, and any sedimentary rock that contains plastic is going to be a clear sign that you’re looking at rock from the Anthropocene.

In addition to all of these chemical traces we’re leaving behind, we’re also just physically changing a huge amount of the surface of the planet, the scientists say. Between deforestation, farming, mining, dams, and modifying coastlines, we’ve transformed more than 50% of the Earth’s land area. All of these things affect how, where, and what gets laid down to form new layers of sediment. And over thousands of years, those layers of sediment will become sedimentary rock.

And the last major factor in making the case for the Anthropocene: mass extinction. Earth has seen five massive die-offs so far, as organisms have failed to adapt to their changing environment. And it looks like it’s happening again. By some estimates, species are going extinct at rates 100 times faster than the normal, background rate that occurs between extinction events. Other research has found that vertebrates are experiencing a 25 percent decline in their total numbers, while invertebrates are dropping by 45 percent. This definitely isn’t the biggest mass extinction on the books. About 250 million years ago, the Permian extinction wiped out 96 percent of all species on Earth, in an event known as “The Great Dying.” But a so-called Anthropocene extinction would still be enshrined in Earth’s rock layers, as many species disappear from the fossil record, while the bones of humans and domesticated animals begin to dominate it.

So, what does all this mean for the future of the Geologic Time Scale? Well, the group that gets to decide what epochs are called is the International Union of Geological Sciences. And they’ve put together a working group to determine, by the end of this year, if we’re living in the Age of Humans. We’ll keep you posted on the future of how we talk about the past.

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