The traces of humanity can be seen all over the planet today, from towering buildings within modern cities to pyramids and other ancient monuments from our past. But what would the world be like if humans had never existed?
Some scientists propose a thriving nature in abundance of currently known and unknown species.
Also, a world without modern humans could also mean that our extinct human relatives, like Neanderthals, would still be around. Which could lead to the same mistakes that Sapiens made. It's hard to say what that would look like.
Humans have shaped the world at the expense of many species that we have driven to extinction through activities such as hunting and habitat destruction. The humanity-led decline of nature indicates that Earth would be a much wilder place without us, with some giant animals still alive.
Moas and Haast eagles are recent examples of large animals whose extinctions are linked to human activities, such as unsustainable hunting and the introduction of invasive species into new habitats.
The survival of large animals is central to speculating about an Earth without humans, as these animals also have an impact on landscapes.
The Land of the Serengeti
Sören Faurby, senior professor of zoology at the University of Gothenburg in Sweden, conducted a study, published in 2015 in the journal Diversity and Distributions , suggesting that without humanity, Earth would largely resemble the modern-day Serengeti, an African ecosystem teeming with life.
In this scenario, extinct animals that were similar to those found in today's Serengeti - including elephants, rhinos and lions - would live all over Europe. Meanwhile, the American continent would be home to giant elephants and bears, as well as unique species like car-sized armadillo relatives called Gliptodon and giant ground sloths.
"In a world without humans, there would be a much greater diversity of large mammals, and if there is a greater diversity of large mammals, there tends to be a much more open habitat," Faurby said.
Elephants and other large animals are pretty determined to find food and won't put up with unnecessary obstacles. "If you're big enough, then it might be easier to just take down a tree and eat the fresh leaves on top," Faurby said.But also, if there are a ton of large mammals, there tends to be less wooded vegetation, he added.
More nutritious earth without humanity
Christopher Doughty, an associate professor and ecologist at Northern Arizona University, models how large animals of the past and present move seeds and nutrients through feeding and defecation. His work suggests that the transport of elements such as phosphorus, calcium and magnesium, which are critical for life, has decreased by more than 90 percent through the extinction of large animals.
Bold hypotheses point out that without humans, the elements would be more evenly distributed. This would mean more fertile soil, which would make ecosystems more productive.
Humans tend to crowd elements together through practices like farming and creating fenced-in areas, so these areas become less fertile over time compared to wild systems, according to Doughty. Higher fertility means plants can produce more fruit and flowers.
The climate may also be different, and while it is difficult to say how humanity and megafauna may have influenced climate change thousands of years ago with evidence obscured by time, it is much easier to judge our impact on Earth's climate today.
Through global warming, caused by activities such as burning fossil fuels, humans have raised the average global temperature by about 1 degree Celsius since the early 20th century. The Earth, therefore, would have been at least colder without us.
A 2016 study published in Nature concluded that human-caused warming will delay an upcoming ice age by at least 100,000 years. However, even without the human delay, it's unlikely that Earth would be in the middle of another ice age today if we weren't around.