No one knows for sure. But those bio-diversity guys are getting closer to figuring out an algorithm that would incorporate the vast estimated number of regularly changing estimated variables needed to make the algorithm work to give us a (still) estimated number that is already wrong by the time the algorithm spits out its answer.
There are a number of issues and problems and just not fair challenges associated with counting species. For instance our data is biased and numbers are all wrong because while we got a decent handle on say birds or mammals we know squat about most of the ewww- inspiring insects no one wants to count or even study. Those smaller animals like the half a million strong ant colony are soooooo hard to count, I keep losing count! And have you tried to get a scientist and researcher to freely share his research so you can turn it into an estimated variable ... oh no no.
- 10,000 species of animals are discovered each year
- Over 1.2 million species already described.
- Some estimates of estimates state with absolute authority that 86% of all land species and 91% of those in the water have yet to be discovered, described and catalogued.
- No reliable estimate for how many are dying.
- No reliable estimate for how many are being born.
- No reliable numbers for how many were eaten, processed or killed right out.
Comprehensive Google Search (that means 1.2 pages) indicates your answer is anywhere from 3 million to 8.74 million to 10.8 million ... Though as I write this the damn animals kept breeding and dying and not coming out to be counted. I gotta start all over.
Your guess is as good as his guess which is as good as my guess and as good a guess as any guess can be.
Hope that clears the waters for you!