It is not easy to determine the speed at which species are currently disappearing from our planet. Believe it or not, we still have a great deal to learn about the Earth's biodiversity. We do not know exactly how many species currently exist, nor can we determine with certainty when a species is truly extinct.

We are too few biologists for such a large world and many, many species may be disappearing without us ever knowing that they existed. However, we are not blind in this matter of species extinction and paleontology allows us to shed some light. In the last 500 million years there have been five prominent events in the fossil record that tell us of major reductions in global biodiversity, interspersed with long periods of species coming(speciation) and going(extinction) naturally.

Well, the extinction rates or fees of mammals, birds, reptiles and amphibians calculated for the last 500 years are higher than those calculated for the five major mass extinctions. For mammals, the background extinction rate (the average time a mammal lasts on our planet) is set at 1 species every 1000 years and in the last 400 years this extinction rate has increased by a factor of 50, reaching 1 extinct species every 16 years.

These figures must be taken with caution, since paleontological extinctions took place over hundreds of thousands or millions of years, while the information we have on the current state is of the order of decades or centuries.

Making large extrapolations from such short time periods can lead to large estimation errors, but it seems clear that yes, we are in the sixth mass extinction of species. What is indisputable is that, unlike the extinction periods of the past, the sixth great extinction will be caused primarily by our actions on the environment. Today, we have reached fees unprecedented levels of deforestation and habitat destruction.

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David Galicia
Professor at department of Environmental Biology, University of Navarra
This article was originally published in The Conversation.