How many different types of living things are there in the world?

I don’t know, but two fellows at Indiana University took a stab at this question. They focused on microbial life, which is smart, because there is more of that than any other kind of life.

Plants are the dominant life form on earth if you measure by mass. The amount of carbon stored in plants is estimated at 450 Gt. Bacteria weigh in at about 70 Gt. Those units are giga-tonnes. The giga- prefix means one billion or 10^9. So a Gt is over two trillion pounds!

A trillion is not an easy number. It’s a lot of zeroes:

1 000 000 000 000

Or if you prefer commas:


An easy way to think of one trillion is “a million times a million.”

I suspect that one million is about as big of a number that most people can visualize. There are about a million seconds in twelve days, for example (12 x 24 x 60 x 60 = 1 036 800).

One million times one thousand will get you a billion. So 12 000 days (~32 years) is about a billion seconds.

One billion times one thousand will get you a trillion. So 12 000 000 days (~32 000 years) is about a trillion seconds.

The latest infrastructure bill from Congress and the President comes to about one trillion dollars!

Back to the first question: how many different kinds of living things are out there in the world?

Biologists Kenneth J. Locey and Jay T. Lennon suggest in their study (“Scaling laws predict global microbial diversity” in PNAS vol. 113 no. 21) that the earth is home to one trillion species of microbes. This does not include insects or mammals or other such creatures. Just micro-organisms.

Now that’s not one trillion total microbes, but rather one trillion different kinds of microbes. As far as the total number of microbes on the planet, that’s a really, really big number. Case in point: the number of bacterial cells in your gut biome is at least as large as the total number of cells in your body.

According to IC Insights, the number of semiconductor devices that will be shipped to users in 2021 exceeds one trillion. This milestone was also achieved in 2018 and 2019, and even in the midst of the pandemic, 975 billion were shipped in 2020. Seems like one trillion is the new benchmark. Here’s a graph:

From roughly 33 billion in 1978 to 1.1 trillion in 44 years is about five doublings. That is, the number doubled every eight years or so. That’s about 9% annual growth! Wouldn’t you like to earn 9% every year?

There are not one trillion different kinds of semiconductor devices of course, but there are certainly many hundreds and perhaps many thousands of them, and that number keeps growing. There are about 9 500 different kinds of mobile phones, for example. If you add in all the bits and pieces that make up these devices the number of different artifacts humans have created becomes enormous. Just imagine all the different kinds of fasteners—screws, nails, nuts, bolts, rivets, etc.—and the staggering variety of objects they are needed for. My head is going to explode. I’m still trying to get a handle on “trillions.”

At some point the manufactured world will exceed the natural world in both number and variety of things. Are you ready for that?

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