By about 10,000 years ago, nearly 100 species of large animals had been recently driven to extinction around the globe. This march of megafauna mortality coincides suspiciously with the arrival of another large animal in their vicinity: humans.

The die-off in South America included giant ground sloths and armadillo-like animals the size of cars known as glyptodonts. And the deaths seem responsible for the dearth of nutrients in Amazon rainforest soils today. So says a study in the journal Nature Geoscience. [Christopher E. Doughty et al, The legacy of the Pleistocene megafauna extinctions on nutrient availability in Amazonia]

Plainly put, these big animals disperse a lot of phosphorous in their feces. Once the big animals are gone, there's no way for the phosphorous to get from one part of the rainforest to another. As a result, the Amazon rainforest even today is struggling to recover from that loss of fertility.

Other parts of the world face the same poop paucity predicament, according to the researchers’ model. But the impact outside the Amazon was less severe, for reasons still unknown. What is clear is that the impact of extinction reverberates down through the millennia, a clear signal that we’ve been living in the Anthropocene for awhile.

—David Biello

[The above text is a transcript of this podcast.]

[Scientific American is part of Nature Publishing Group.]