How many different species are on earth?

If mankind were to visit Mars and find life, among our first questions would be how many different forms of it exist there. Ironically though, this is not a question that we can answer about our own planet.

 

On earth, life is on the bottoms of the ocean, it is floating on the dust in the atmosphere, and it is found in every crevice in between. Try as we might, it is nearly impossible to count all the species. But so far, we have cataloged over 1,600,000 of them. And we can only estimate how many are yet to be  found and identified.

 

Back in 2011, a group of scientists actually did produce such an estimation. Their approach to doing this was a bit like estimating the number of jellybeans in a jar based on how many are visible, and doing so for each color. Except with way more sophisticated math.

Based on the number of known species cataloged at the time, they came up with the estimate of 8,749,900 species, not counting the microbes (bacteria and archaea).

 

If we were to break this number down into the classification groups (plants, animals, etc.), it would look like this graphic below. It’s mostly animals, which includes all insects, spiders, and other crawly things.

 

Now, let's talk about the microbes - all the creatures we can't see. In May 2016, a couple of other researchers came up with a new estimation for those guys: 100,000,000,000 species (or, 100 billion). And this is the low end of their estimation*. 

 

To put this in perspective, here’s how that number compares to the 8,749,900 forms of higher life shown above (eukaryotes).

 

You can see how the number of more complex species is almost insignificant.

 

This amount of microbial diversity is incomprehensible. To me, it seems impossibly high. But how would I know? I can’t see all the microbes around me (and inside me). That is part of what makes this a tough estimation to make. The other part is that at the microbial level, it is difficult to distinguish one species from another when you are trying to classify them. A given species of bacteria will usually have many different strains, and it’s a fuzzy genetic line sometimes that separates a 'strain' from a 'species'. Microorganisms are indifferent to our attempts to classify them. They just are what they are, and they are evolving.

 

In any case, consider that as human beings, we are only one of billions of species on a planet where "life finds a way". Lots of ways. In a universe that is otherwise sterile for as far as we can see, we should be humbled by the diversity of life that surrounds us. If we protect life in all of its forms, there is still much we can learn from it.

*I used the lower end of the estimation because it included microscopic fungi, which were also included in the 8,749,900 value. The upper estimation was 10-fold higher: 1 trillion.