We often hear people say that the amount of life in the universe is infinitesimal compared to the mass of the stars and, above all, the empty space. But doesn’t that really depend on how you want to count things?

What if we try for a rough comparison between the number of living cells and the number of, say, stars?

Last year, at Science, Elizabeth Pennisi reported,

From bacteria to blue whales, the number of cells in living things exceeds the estimated number of sand grains on Earth by a factor of a trillion. It’s 1 million times larger than all the stars in the universe. And the number of cells that have ever lived is 10 orders of magnitude larger still, according to new estimates researchers reported last week in Current Biology.

“New calculations say there are more living cells than grains of sand or stars in the sky,” October 17, 2023

The authors at Current Biology (Crockford et al.) estimate that “10³⁹–10⁴⁰ cells have occupied the Earth to date…”, based on photosynthesis rates.

Pennisi tells us, “Peter Crockford, a geologist at Carleton University, and his colleagues began their inventory by combining existing estimates of the number of microbes currently in the ocean, soil, and Earth’s subsurface with the number of cells in larger organisms. The result was the number of cells alive today.” (“More living cells”)

As Tibi Puiu points out at ZME Science, we can put that ever-so-slightly in perspective by noting that The human body alone contains around 30 trillion cells.

Are further increases sustainable?

Crockford et al. Also believe that Earth simply cannot support more than 10⁴¹ cells. But surely it’s hard to know. Puiu tells us,

The story begins over three billion years ago, when cyanobacteria first evolved. For nearly two billion years, these microbes were Earth’s primary photosynthetic organisms, capturing sunlight and transforming it into chemical energy. Around 800 million years ago, algae emerged, outpacing cyanobacteria in productivity. Then, 450 million years ago, land plants came into the picture and changed the carbon cycle, vastly increasing the planet’s biomass.

“Mind-Blowing Calculation Shows Living Cells Outnumber All the Stars and Grains of Sand — By far,” December 5, 2024

What chance that someone would have said back then that those land plants were bound to kill the planet — if anyone had been around to say it?