Life on Earth has suffered five mass extinctions of biodiversity in its long history, caused by massive volcanic eruptions, deep ice ages, meteorite impacts and clashing continents. But some scientists believe a sixth mass extinction has now begun.
This one is very different, caused not by geology or natural climate change, but by a single species – us. Humans and our livestock now consume 25-40% of the planet’s entire “primary production”, i.e the energy captured by plants on which all biodiversity depends. We have become a voracious top predator across the entire globe.
One estimate suggests that, by weight, 97% of the world’s vertebrate land animals are now either humans or our farm animals – just 3% are wild. Another consequence of this domination is that humanity is driving evolution in many places, most obviously in domesticating crops and animals, but also through genetic modification and even by how we choose to run wildlife reserves.
Furthermore, the intricate jigsaw of life, constructed over hundreds of millions of years, has been thrown into disarray in the last 10,000 years by humans relocating species around the world. These invasive species can devastate ecosystems that have never developed defences – from rats devouring albatross chicks in their nests to snakehead fish decimating native species across the US.
However, not all scientists agree the sixth mass extinction has begun and there’s a very long way to go before we reach the 95% extinction rate seen in The Great Dying, 252m years ago. But what all researchers agree is that current biodiversity losses mean we are heading in that direction.