What fossils will modern-day civilization leave behind?

Millions of years from now, advanced humans—or perhaps visiting aliens—may dig up the remnants of today’s civilizations. What are they likely to find, and how will they interpret our relationship with the creatures around us?

A new study in Anthropocene offers some clues. Karen Koy, a paleobiologist at Missouri Western State University, and Roy Plotnick, a paleontologist at the University of Illinois, Chicago, reviewed nearly 200 papers on fossilization, burial practices, livestock processing, and more.

Science chatted with them about some of their biggest predictions. This interview has been edited for clarity and length.

Q: Who exactly will be discovering these fossils millions of years from now? Advanced humans? Aliens?

Roy Plotnick: Well, of course that begs the question: Will humanity survive that long? And being a sci-fi fan, I’m going to be optimistic and say, yeah, probably we will—that our descendants at some point in time will be looking back. I think that’s more likely than aliens, at least.

Q: With modern humans documenting every second of our lives, will fossils even be necessary?

R.P.: If you read a lot of postapocalyptic science fiction, one of the things that disappears in almost all cases is written records, computer records, things like that. So what are we left with? It’s whatever is buried in the ground.

Karen Koy: And even when you have those records, they often can’t be decoded. Somebody recently started to decode records from a South American civilization that were coded in knots in various types of string or yarn—and it is thousands of years old. There are computer records and code from decades ago that modern computers can’t recognize because it’s so far out of alignment. So imagine 2 million years from now.

Q: In the paper, you mention that the places where fossils have formed in past eras are different now. How?

R.P.: If you look at the natural patterns of where fossils are formed, it’s in caves, any kind of wetlands site, river channels, oxbow lakes, or marsh environments—and all of those have been heavily modified by human activity. Humans dam rivers, we drain marshes. There’s a lot of human modification of the natural surface environment to an extent that researchers suggest is at least as great or greater than natural processes.

Q: You write that when humans and present-day animals die, they leave a distinctive “Anthropocene corpse signal.” What does that look like?

K.K.: The human population took off in the mid–20th century, thanks to modern medicine and antibiotics. And that means a lot more people being buried in an orderly fashion in graveyards. It’s not a mess of bones like we see with dinosaurs. These ordered graves are essentially worldwide, so you’ll be finding people’s remains the same way all over the place. I don’t know if “creepy” is quite the right word, but imagine you’re an alien from another species and you find this world just covered in these bodies all laid out in a specific way all over its surface; just imagine what that would look like.

Q: What animals are most likely to show up in the future fossil record?

R.P.: Certainly chickens, because there are a lot of them. And cows and pigs for the same reason. The sheer number of humans, pigs, and cows is just unbelievable. There’s no population of wild creatures that even comes close.

Q: How might future paleontologists distinguish domestic animals from their wild predecessors?

K.K.: When we’re breeding for meat, we tend to breed for muscle mass. So you’re expecting the bones to be thicker to support the heavier body weight of the animal. For domesticated animals like dogs and cats, we’re going to breed for cute things, like dogs with the pushed-in snout and bigger eyes. So depending on what they were bred for, there’s different sets of things you could actually look at that would potentially allow paleontologists to say, “This could have been a domesticated species or this could be livestock bred for meat or labor.”

Q: What do you think future archaeologists will make of our relationship with cats and dogs, based on what they see in the fossil record?

K.K.: Of all the animals, dogs and cats are more likely to be buried in a manner similar to people. There are pet cemeteries that are set up similar to human memorial parks. So if anything like that is stumbled upon, that’s going to say something different than a pit that people threw a bunch of pigs into randomly. I think it’s going to be obvious that we felt differently about dogs and cats versus pigs and cows and chickens.

R.P.: Will they think we worshipped them? I have no idea. Religious explanations seem to be a stock answer, but hopefully future researchers are more sophisticated than that.