Plastic and chicken bones. These are two of the biggest pieces of evidence of deep human activity on the planet that wouldn’t be around if humans never existed. While researchers find plastic bags and other waste even in the deepest places on Earth, such as the Mariana Trench, estimates point out that there are 23 billion chickens in captivity on the planet.
These are two small – but very significant – examples of how the human species has been changing the biosphere over the last few thousand years. However, what would the planet look like now if our primate ancestors had never evolved and eventually given rise to the Homo sapiens?
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Well, the African savannah could be the most common type of environment on Earth. The difference is that the biodiversity of mammals would be extremely higher, as shown by recent research (PNAS, Diversity and Distributions).
This is because the human species was responsible for the extinction of most of the megafauna that inhabited the planet in the last Ice Age. In North America alone, 38 genera of large animals became extinct at the end of the last glacial period.
That is, the surface of the planet would be much more open, since large animals would walk around cutting down trees and vegetation. Furthermore, saber-toothed and North American lions could still be hunting in the plains of Europe, Africa and even the Americas, where there are no lions today.
Mammoths and great ancestors of elephants would probably still be here. Although research shows that climate change (not that caused by humans) has wiped out the mammoths, researchers still claim that we played an important role in reducing the population of these hairy elephants.
Giant sloths, huge crocodiles and armadillos the size of small oxen would also be roaming the Americas to this day. If humans had never existed, ocean pollution would also be virtually nil, and the seas would probably be the most diverse habitat on Earth.
Another way to think about the impact of humans on the planet is to imagine what the planet would look like going forward if we just disappeared from the face of the Earth.
If humans had never existed or were extinct now, an obvious relief for the planet would be the reduction of carbon in the atmosphere. It is likely that the planet and the organisms here themselves took more than 60,000 years to remove all the carbon that H. sapiens produced from the atmosphere.
One of the great implications of a world without the species and human, therefore, is the significant reduction of the greenhouse effect. This would certainly favor a cooler planet with less variable short-term climate cycles. An upcoming ice age could even happen much sooner than expected.
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