Humans dominated the Earth even thousands of years ago. Prehistoric settlers have spread like invasive species with their population surging then crashing as they persistently exhausted natural resources, a new study found.

In a study published in the journal Nature, researchers from Stanford Woods Institute for the Environment found that human populations in the continent grew like invasive species that are controlled by the environment.

For instance, the population would grow exponentially when they first colonized South America toward the end of Ice Age. Then the populations abruptly decreased, improved to some extent and plateaued for thousands of years when the settlers learned how to grow crops and raise domesticated animals.

The study provided a detailed look of how people settled and invaded South America, the last habitable continent colonized by mankind.

The researchers identified two distinct phases of colonization. The first one happened about 14,000 to 5,500 years ago with human populations surging to 300,000 and the second phase occurred about 5,500 to 2,000 years ago with the population reaching about 1 million.

Earth's Carrying Capacity

"The question is: Have we overshot Earth's carrying capacity today?" said Elizabeth Hadly from the Stanford Woods Institute for the Environment and co-author of the study.

This is because humans respond just like other invasive species. This means that human populations could crash before stabilizing a global population size.

The threat of mass extinction still linger today as natural resources continue to be depleted and environmental conditions worsening. The study sheds light on how humans added to the biggest extinction of big mammals during the Pleistocene era.

"Thinking about the relationship between humans and our environment, unchecked growth is not a universal hallmark of our history, but a very recent development," said Amy Goldberg, study co-author.

Will Populations Crash Again?

At present, with surges of populations across the globe, humans may exhaust and deplete the natural resources the planet can offer. With the help of technology, humans can reset the Earth's carrying capacity to harvest or create new resources.

If humans continue to invade the planet, can it sustain life in the future? If yes, for how long?

Photo: Douglas Scortegagna | Flickr