Poof! The apocalypse happens, and humanity disappears. It’s a staple of science fiction and every doomsday prepper’s dread. If Earth’s abandoned places are any indication, nature would soon overtake our architectural triumphs and winding networks of roads. So if the planet’s surface reverts to a natural Eden, what human fingerprints might become buried in layers of rock for future geologists to uncover?
The usual suspects include widespread species extinctions, nuclear fallout, acidified oceans and drastic climate change. But human growth and innovation have also led people to make changes to our surroundings that are less well known—and sometimes a little bizarre. Here are six of the more intriguing ways humans are altering the planet:
Deep Holes and Shorter Mountains
Plenty of species spend their time digging. Trace evidence of subterranean burrowing even shows up in the fossil records of marine environments. But humans may have all other excavators beat. A study published in July in the journal Anthropocene argues that holes might be humanity’s most lasting impact on the planet.
While most mining projects only extend a few hundred feet into the earth, some mines for coal, precious metals and other minerals really take the plunge. Gold mines in South Africa, for instance, can reach depths of 2.5 miles. Boreholes made by oil and natural gas drilling average several thousand feet. Waste storage and underground nuclear testing will also leave an imprint on Earth’s subterranean environment. Underground transportation and sanitation infrastructure lies at shallower depths but is out of reach of erosion, so may have a modest chance of being preserved.
Human influence is also being felt at great heights. The controversial method of mountaintop mining has been practiced in the Appalachian region of the U.S. for decades. It involves blasting off the peak of a mountain or hill to reveal seams of coal beneath. And China is using similar mountaintop removal methods to make room for its rapidly growing cities. A project in Yan’an aims to double the city’s available land by removing nearby hills that are above 328 feet high—creating more than 19,000 acres of flat land. Researchers warn that such projects could come with serious geological and environmental consequences.
Fat Turkeys, Sweet Corn
Humans have been cultivating and domesticating plants and animals since the dawn of agriculture, around 10,000 B.C.E. And people have been cross-breeding different species and cultivars to artificially select for specific traits for almost as long. Take the turkey: Thanks to changes in diet, vaccines and artificial insemination, breeders have created a much larger bird than its wild relative. Today’s commercial turkeys are more energy efficient when it comes to converting feed to body weight, giving them much larger chest muscles. However, these birds have trouble walking, can’t fly and are no good at regulating their food intake.
Crops are also drastically different from their wild counterparts. Corn grown today is significantly sweeter than maize consumed a few centuries ago. A genetic mutation that replaces some of the grain’s starch with sugar gave us sweet corn, which was grown by the Iroquois and passed on to European settlers in 1779. Subsequent revelations about corn genetics have allowed farmers to breed even sweeter varieties. The opposite is true of potatoes, which have been bred to be starchier for better cooking and frying.
Then there are crops and a handful of animals that have undergone genetic engineering, including Rainbow papayas made resistant to viruses and soybeans that can tolerate herbicides and pesticides. Though precautions are taken to prevent these genetic variants from drifting into wild ecosystems, it’s unclear how modified plants might fare if left unchecked. And engineered or otherwise, crops have lost an estimated 75 percent of their genetic diversity over the last century, which makes it harder for staple breeds and cultivars to adapt to environmental change, drought or disease.
Environmental scientists and geologists may debate when the Anthropocene began in the rock record, but recent evidence suggests that humans have left one pretty obvious mark: plastic rocks. In the June issue of GSA Today, scientists announced the discovery of rock fragments made, in part, of plastic detritus at Kamilo Beach in Hawaii.
Humans have been making loads of synthetic plastic since the 1950s, and its accumulation in the water is a growing problem. Estimates suggest that the ocean contains between 40,000 and 1 million tons of plastic. At Kamilo Beach, plastic fishing line, bottles, confetti, bits of tires and other products that were left behind or washed ashore found their way into the vicinity of campfires. The fire melted the plastic along with nearby coral material, sand, shell fragments and woody debris, melding it all into pieces of stone dubbed “plastiglomerate”.
The researchers behind the paper posit that globally, other high temperature situations like forest fires and volcanic lava flows could also provide the right environments to create similar plastic rocks. Given plastic's pervasiveness on Earth, it’s possible that plastic rocks might become a geological landmark. But rocks also undergo severe temperature and pressure extremes as they become part of Earth’s strata. Some plastics might revert back to oil or persist as thin films of carbon.
Frozen Pollution in Ice and Snow
Ice cores are a lot like tree rings. Layers compacted in ice sheets or glaciers can tell us about what Earth was like when that ice was newly fallen snow. Cores drilled in Antarctica date back 800,000 years, while those drilled from Greenland’s ice sheet provide records as far back as 108,000 years ago.
Ice layers can contain chemicals and tiny air bubbles that provide a snapshot of what was floating around in the atmosphere, and the thickness of the layers indicates snowfall rates. Ice cores drilled today contain radioactive elements from the Chernobyl nuclear incident in 1986 and from atomic bomb testing in the mid-20th century.
Ice cores also document the heavy metal pollution from human industrialization. A study published in July in Scientific Reports found that traces of lead have been showing up in Antarctic ice since 1889. Based on its chemical profile, the researchers traced some of that lead to deposits near an old mining town in Broken Hill, New South Wales, Australia. According to the data, lead pollution saw two spikes in the 20th century, first in the 1920s and again around 1975. Today lead shows up at lower levels, but still much higher than the amounts seen before the industrial revolution. In total, Antarctica has collected about 660 tons of lead over the last 130 years.
Space Junk in Low-Earth Orbit
On October 4, 1957, humanity launched its first satellite into space: Russia’s Sputnik 1, which was about the size of a beach ball. More than 50 years later, low Earth orbit is packed with working satellites and loads of space-age debris, such as discarded rocket parts and broken or retired satellites. The U.S. Space Surveillance Network and other organizations track roughly 500,000 pieces of “space junk” as they orbit the Earth, moving as fast as 17,000 miles per hour.
For space junk, the biggest problem is collisions with other orbital objects. Any fragment of space debris bigger than a centimeter can pierce the wall of a working spacecraft or a satellite. And even small collisions create additional dangerous debris. In 2007, China launched a ballistic missile at its own weather satellite to test defensive technology, while two communications satellites (one American, one Russian) collided in 2009. These two events are responsible for about one-third of existing space debris today.
Orbits decay over time, causing space junk to fall back to Earth, and most pieces burn up when they hit the atmosphere. But higher altitudes make for longer time in orbit. Debris at about 370 miles returns to the ground within a couple years. Anything higher than 620 miles will spend a century or longer in space. Though no one’s been tasked with removing space debris, a few companies and researchers have dreamed up potential trash removal strategies, ranging from orbital tugboats to giant nets to lasers.
Flying Sheep and Swamp Pythons
In 2012, police caught a helicopter pilot flying axis deer from Maui to the Big Island of Hawaii. The flight was part of a smugglers’ scheme to improve hunting sport on each island by swapping the deer, found on Maui, for mouflon sheep from the Big Island. Both species are native to the Mediterranean, and both pose considerable threats to Hawaii’s native ecosystems.
The interrupted airlift is only one of the ways humans have transported exotic species to disparate parts of the globe. In 1884, a horticultural exposition in New Orleans included a water hyacinth (Eichornia crassipes) specimen from the Amazon. A hit with local gardeners, it quickly colonized aquatic ecosystems across the Southeastern United States. Though the full extent of its impact is unclear, water hyacinth sits on the surface, shielding other aquatic plants from sunlight and other resources. More recently, around 150,000 Burmese pythons (Python molurus bivittatus), native to Southeast Asia, have colonized the Florida everglades. They were probably introduced by the escape or purposeful release of pet pythons. With little competition for resources, the snakes are thriving on a diet of local aquatic birds and even alligators.
Every case of species invasion is unique. Some creatures were introduced by accident, stowaways aboard cargo ships or caravans. Others were human attempts to biologically control local pests or even other invasive species, like the cane toad in Australia. But the overall effect is a distinctively rapid movement—and sometimes removal—of species on Earth.