When geologists of the future dig down into the layer of Earth that represents our current time, what will they find? A new review of previous studies answers: There will be a lot more plastic and concrete than ever existed before, plus black carbon from the burning of fossil fuels, and chemical ghosts from the nuclear testing of the 1950s and '60s.
The review, published today in the journal Science, isn't meant to provide fodder for your great American alien geologist romance novel. (Just give me a shoutout in the acknowledgements, thanks.) The study's authors sought evidence that the Earth is in a whole new epoch. That's a big deal. Epochs usually last tens of millions of years and are defined by fundamental shifts in the Earth's chemistry and life forms. In previous epochs, natural forces drove those shifts. In the early 2000s, however, chemist Paul Crutzen proposed that human activity has altered the Earth enough to push us into a new time, which he dubbed the Anthropocene. The word combines the prefix for "human" with the suffix that appears in the names of Earth's previous epochs, such as the Pleistocene and the Pliocene.
What are the chemical signatures of the Anthropocene? For starters, there's aluminum.
Scientists have since debated when the Anthropocene started and whether to register the epoch officially. Some researchers think the term is more useful for political ends than scientific ones, while others say it helps scientists to grapple with just how drastically people are able to alter the Earth. The authors of the Science review make the case that the Anthropocene started in the mid-1900s. They also write that the Anthropocene does appear quite different from the Holocene—the epoch we're in now—but there's a lot of work left to do before registering the human epoch with the International Commission on Stratigraphy.
That's all fine and dandy. Now let's look at the really interesting stuff. What are the chemical signatures of the Anthropocene? For starters, there's aluminum. Aluminum is a naturally occurring element, but was rare before the 19th century. Since 1950, humans have produced 98 percent of all the aluminum made on Earth. There's also much more nitrogen and phosphorus in the soil now, a result of human-made fertilizers. Of course, the burning of fossil fuels has altered the chemical composition of the world's ice and soil in many ways, depositing into it particles of black carbon and lead from leaded gasoline. Lastly, Cold War-era nuclear tests noticeably increased levels of plutonium and carbon-14 in the Earth's crust. The review authors propose plutonium fallout as the marker for the start of the Anthropocene.
For most of us, whether the Anthropocene gets official recognition doesn't really matter. Either way, it's enough to know scientists are considering it—and what goes into it, and into our land now.
Quick Studies is an award-winning series that sheds light on new research and discoveries that change the way we look at the world.