I remember being taught (funny how memory works) that greater than 95% of all species that ever lived on Earth are extinct.  I have passed this information on for years, until recently when someone asked how that number was reached.

So my question is, what is the estimated number of species that have ever existed on Earth?  How was this number achieved? What percentage of all those species is extinct?

Thanks for your time,

Bart Mitchell

I think the actual figure is 99.99...% and if I remember correctly it was the (now retired) David Raup who first made this statement. However, this was never intended to be an exact figure, in fact it can't be as we don't know either of the key numbers to calculate it.

The first of these is, how many species are alive today? So far we have named about 1.5 million, but we are still finding more, so we can only really guess what the final total will be.

The second is, how many species have ever lived? Here our best guess would have to vary wildly. Even if we found and named every fossil, there are countless more that never left any remains behind.

Raup was simply stating that the second number was likely to be significantly more than the first. Although there is a degree of guessing here, I don't think there is any reason to doubt the accuracy of Raup's statement. Life has been around for a good 2 billion years at least, but most species only seem to last for a few million years. Thus, even if global species diversity had remained at one for the whole of life's history there would still be a far greater proportion of extinct ancestral species than the single living descendant species.