Scientists mapping the total mass of organisms on the entire planet have discovered humans make up just 0.01 percent—dwarfed by the mass of bacteria, fungi, earthworms and plants.
Barely a sliver of the planetary pie, humans have nevertheless driven the extinction of ancient megafauna, countless modern animals and even plants, the researchers report in the journal Proceedings of the National Academy of Sciences.
If you add up all the carbon in all the living organisms on Earth, you can estimate the planet's total "biomass." The researchers think Earth has a biomass of about 550 gigatons—that's 550 billion tons of carbon.
Plants, they estimate, make up more than 80 percent of this biomass—of which just 2 percent are human-cultivated crops. Bacteria make up about 15 percent of the total biomass, while everything else accounts for just 5 percent. Almost all life, the team estimate, is land-based, with just 1 percent living in the oceans.
The scientists think humanity may be to blame for the loss of more than 80 percent of wild mammals and about half of all plants. Deforestation, overfishing and hunting are just a few of the ways humans are decimating wild species.
Livestock, on the other hand, is booming. The authors estimate that about 60 percent of our planet's mammals are livestock, The Guardian reports. The total biomass of domesticated birds, including chickens, is three times higher than the biomass of wild birds, the authors think.
“I would hope this gives people a perspective on the very dominant role that humanity now plays on Earth,” lead study author Ron Milo from the Weizmann Institute of Science in Israel told The Guardian. "It is definitely striking, our disproportionate place on Earth."
Milo was shocked to find a comprehensive census of Earth’s biomass didn’t already exist, he told The Guardian. By scouring the available scientific literature, his team was able to create its census.
“It’s what you could call a meta-meta-analysis,” Milo told New Scientist. “It’s based on hundreds and hundreds of papers. We also consulted with many, many experts.”
Although the team accounted for a degree of uncertainty in its work, biomass expert Vaclav Smil, author of Harvesting the Biosphere, thinks it has overestimated its grip on the unknown. He told New Scientist: “I am all for integrative biosphere-scale studies, but we have to be always honest about the limits of our knowledge.”
You can calculate the biomass of some organisms—crops, livestock and humans—reasonably well, he said. But “for all other terrestrial and marine fauna, the figures get much more shaky. For insects, bacteria and viruses, they remain essentially the best guesses.”
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