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What Weighs More – Bacteria or Every Single Person on Earth?

Plus the slightly icky notion that biomass is measured “wet” or “dry.”

18 years ago, a research team at the University of Georgia put on their thinking hats in an effort to estimate the number of bacteria on earth.

Sensibly, they decided against trying to count them all, for it was what you might call one heck of a big number.

5 million trillion trillion, in fact, or a 5 followed by 30 zeros.

Here, allow me:

5,000,000,000,000,000,000,000,000,000,000.

They helped put this into perspective for us mere mortals by calculating that if each bacterium were represented by a penny, and those 5 million trillion trillion pennies were placed on top of each other, the stack would be a trillion light years high.

Way bigger than the observable universe, in fact.

Since 1998, when this gigantic figure was computed, there’s been an alternative view, um, floated by a team of scientists from the University of Rhode Island’s Graduate School of Oceanography who suggested in 2012 that there may be a lot less bacteria in the floor of the ocean than had previously been imagined.

They actually based this on surveys which dug holes under the sea.

But as it’s largely agreed that the great majority of Earth’s bacteria live on land rather than in the ocean, even this more recent finding doesn’t alter the fact that we share our planet with what you might call a mountain of microbes.

A boatload of bacteria.

All of which brings us to what biologists call biomass, and what we might describe as the weight of all living things.

Rather yuckily, biomass can be measured “wet” or “dry,” and this choice applies to everything that lives, including you and I.

I’m not, of course, talking about whether you weigh more just after you step out of the shower, but the fact that we’re all actually made of water – well, to a large degree anyway.

By weight, the average human adult male is around 69% water.

A 190 pound male, therefore, is made up of about 15.6 gallons of H2O – 15.6 gallons being, curiously, exactly the size of the fuel tank on a 2012 Chevrolet Cruz.

But let’s return to bacteria.

How does the biomass of bacteria on the planet compare to other living organisms?

A 2012 estimate of the total “wet” weight of all humanity is 350 million tonnes.

All the ants on Earth may weigh as much as 300 million tonnes, so we humans only just outrank them.

However, termites have us beat.

Add them all together and you’d have about 445 million tonnes of the little creatures.

And just when you thought it couldn’t get any heavier, along come Antarctic krill.

Seriously?

Yup, these tiny aquatic creatures amount to a ginormous 500 million tonnes of biomass.

So what about bacteria, then?

Well, prepare to have your mind blown.

Although the 1998 estimates have been questioned in terms of ocean-dwelling microbes, the University of Georgia researchers suggested that the DRY biomass of bacteria is between 350,000 and 550,000 million tonnes.

Since the dry biomass of humans is only around 105 million tonnes, the bacteria on Earth weigh at least 3,000 times as much as all of humankind combined.

And I suppose this shouldn’t actually surprise us when we stop to reflect on the fact that there are about 50 million bacterial cells in a single gram of soil, and estimates suggest that over 90% of all bacteria on Earth live in the soil.

In fact, someone who may well have had too much time on their hands calculated that the world’s soil bacteria weigh as much as the United Kingdom, although working that out couldn’t have been easy.

I mean, how do you weigh Wales anyway?

Let’s just finish by reminding ourselves how much bacteria you have in – and on – you right now, casting no aspersions on your personal hygiene of course.

The folks at the Human Microbiome Project estimate that all your personal bacteria probably weigh in at between two and six pounds, enough to fill a large soup can, and consisting of something like 100 trillion cells.


Further reading

Biomass (ecology)

Biomass of termites and their emissions of methane and carbon dioxide: A global database

First-Ever Scientific Estimate Of Total Bacteria On Earth Shows Far Greater Numbers Than Ever Known Before

Global distribution of microbial abundance and biomass in subseafloor sediment

Improved Estimate of Earth’s Total Biomass

New estimate of living biomass: One third less life on planet Earth

Observable universe

Planet bacteria

URI oceanographers find there is one-third less life on Earth

Which life form dominates Earth?