|Fossil records of mammals will provide a clear mark of the so-called Anthropocene era or the period of when the number and technology of humans have grown to surpass the impact of natural processes / Photo by: Elena Miroshnichenko via 123RF|
Just like earlier civilizations, modern humans will leave traces of themselves behind for future generations to dig up and study millions of years from now. But what will they find, and what will these findings say about modern human's relationship with the world around them?
Researchers say that when present-day humans and animals die, they will leave a distinctive "Anthropocene corpse signal"—orderly graveyards of human fossils.
Fossil records of mammals will provide a clear mark of the so-called Anthropocene era or the period of when the number and technology of humans have grown to surpass the impact of natural processes.
Signaling the Anthropocene Era
Researchers from Missouri Western State University published a paper that reviewed 200 papers on fossilization, burial practices, livestock processing, and more to predict what fossils modern society will leave in the future.
They assessed the International Union for Conservation of Nature (IUCN) list of Least Concern (LC) and Near Threatened (NT) species—which are still "widespread and abundant" in the wild—to determine the number of species that will contribute to the potential fossils record.
"The chance of a wild animal becoming part of the fossil record has become very small," paleontologist Roy Plotnick, a co-author of the study, said in a statement. "Instead, the future mammal record will be mostly cows, pigs, sheep, goats, dogs, cats, etc., and people themselves."
The researchers found that out of the 5,574 total species on the list, 3,233 (56.9%) are LC and another 347 (6.1%) is NT. This finding suggests about 2/3 of all mammals on the IUCN list will likely contribute to the future fossil record.
In comparison, the potential inclusion of humans on the record is significantly high, considering there are currently 7.7 billion in the world today—and the population will grow up to 11 billion in the next thirty years.
Domestic livestock also has a higher probability of being on the record since their distribution pattern and population growth closely follow that of humans. With intensive farming methods, global estimates show an increase in livestock production of up to 50% by 2040.
Fossils of domestic pets will also surpass that of wild animals, with an estimate of the worldwide population of dogs currently at 900 million and cats at up to 600 million.
Changing Preservation Sites
For centuries, humans buried most of their dead in cemeteries. However, their activities have also changed how and where animals are laid to rest.
Shifts in land use and climate change, production of landfills and cemeteries, and changes in the breakdown of both animal and human carcasses altered the distribution and properties of naturals sites of preservation.
In the study, the researchers identified the preservational environments where mammals species from the IUCN list were buried. They found that at least 938 (1.8%) species on the list have at least one occurrence sites on the Paleobiology Database (PBDB).
The preservational environments were grouped in 10 categories: Cave; Other Karst (e.g. sinkholes and fissure fills); Lacustrine and Wetland; Fluvial; Eolian; Tar; Glacial; Coastal; Marine; and Terrestrial Indeterminate.
Of these sites, they found that preservation mostly occurred in caves (2,629 occurrences) followed by indeterminate terrestrial (1,528), other karst (604), and fluvial (576).
Modern times are changing these preservation sites. For animals, their carcasses may end up in landfills, reducing them to unidentifiable fragments, or cemeteries.
"Fossil mammals occur in caves, ancient lakebeds, and river channels, and are usually only teeth and isolated bones," Plotnick said. "Animals that die on farms or in mass deaths due to disease often end up as complete corpses in trenches or landfills, far from water."
|For centuries, humans buried most of their dead in cemeteries. However, their activities have also changed how and where animals are laid to rest / Photo by: Patrick De Grijs via 123RF|
The researchers say the fossils that modern humans will leave will be novel in the Earth's history. They will also be unmistakable to paleontologists 100,000 years from now.
That unmistakable pattern is thanks to modern medicine and antibiotics that drove the growth of the human population. With that growth comes a more orderly fashion of burying the dead.
"It’s not a mess of bones like we see with dinosaurs," Karen Koy, a paleobiologist and co-author of the study, said in an interview with Science Magazine. "These ordered graves are essentially worldwide, so you’ll be finding people’s remains the same way all over the place."
Koy also explained how future paleontologists might distinguish domestic animals from wilder species. Livestock fossils will likely have thicker bones to support their heavy bodyweight, considering that humans breed meat for muscle mass.
This changes for animals like cats and dogs. For their domesticated relatives, they will likely have a pushed-in snout and bigger eyes since humans usually breed them to be cute.
"So depending on what they were bred for, there [are] 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.'"