Earth could be on the verge — on a big picture timescale at least — of only the sixth mass extinction in its history, according to research led by the University of California at Berkeley.

For the terms of the research, a mass extinction is defined as 75% of the different species on the planet becoming extinct within a short period. That’s a short period in historical terms, though, meaning a couple of million years at most.

The last of five such known events is thought to have been when an asteroid hit Earth around 65 million years ago in what’s now Mexico and led to the wipeout of  the dinosaurs (pictured above in artist rendition).

The researchers attempted to compare findings from fossils that tell us about when previous species were lost during mass extinction events, and records of species in comparatively recent times. It’s an inherently limited operation as humans are only actively tracking the status of around 2.7% of all current known species.

The findings were that in the past 200 years, only a couple of percent of species have gone extinct. The problem is the overall rate of extinction (that is, how quickly species are dying out compared with how quickly new ones are developing): it’s thought to be somewhere between three to 12 times higher than in historically “ordinary” circumstances.

Clearly there’s a significant margin of error with such extrapolation. The key to the various numbers seems to be (to put it in extremely simple terms) that extinction is on the rise but isn’t yet critical. However it could be as little as a few hundred years before the momentum becomes irreversible.

The other significant note from the research is that, unlike previous mass extinctions caused by natural events, the causes this time are largely man-made such as pollution, overfishing, driving creatures from their habitat, and climate change (to whatever extent man has contributed.)