Scientists Yinon M. Bar-On, Rob Phillips, and Ron Milo tried to answer that question. They estimated the amount of carbon stored in organisms — that is, our planet’s biomass: wild birds, viruses, fish, plants, fungi, etc. Overall, it amounts to roughly 550 gigatons of carbon. Their paper, “The biomass distribution on Earth,” was published in Proceedings of the National Academy of Science of the United States of America on May 21, 2018.
The numbers are rough but revealing. The authors come to several conclusions, including “the mass of humans is an order of magnitude higher than that of all wild mammals combined.”
You can see it in the chart. Humans amount to 0.06 gigatons. We outweigh wild mammals, which are a mere 0.007 gigatons; our livestock outweighs us both together at 0.11 gigatons. Wild birds amount to 0.002 gigatons, while domesticated poultry weigh three times more.
Plants rule the planet at 450 gigatons of life, but the authors of the study estimate that since the start of human civilization, the total biomass of plants has fallen to half its previous level.
You can read the six-page article at PNAS or reports about the article at The Economist and Vox. Vox has created an especially easy-to-understand chart. The Economist explains briefly but carefully the enormous impact that human beings have had on the planet.
We rule the Earth and have changed it in ways we don’t notice day to day. The big picture is instructive. It tells us how a single species can entirely reshape the structure of life on a planet.
— Sue Burke
P.S. On a related note, this article at Bloomberg shows how land in the United States is used: pastures, forests, crops, urbanizations, and special uses like parks, roads, and golf courses. Most land is used as livestock pasture/range. Considering the weight of livestock, this comes as no surprise.