The Earth’s biomass is estimated as 550 gigatons of carbon (GT C); of that what is the weight of humankind?

In terms of gigatons of carbon, humans constitute 0.06 GT C of the Earth’s biomass weight - 0.0001% of the total.

Yinon M. Bar-On and Ron Milo of the Department of Plant and Environmental Sciences, Weizmann Institute of Science, Israel, together with Rob Phillips of the Department of Physics, California Institute of Technology, Pasadena, U.S., published a research paper in PNAS June 19, 2018 (PNAS – “Proceedings of the National Academy of Sciences of the United States of America”, the world's most-cited multidisciplinary scientific serial) entitled “The biomass distribution on Earth”.

Their study sorted all the life on Earth by weight (measured in gigatons of carbon, the signature element of life on Earth). It was estimated that there are 550 gigatons of carbon (GT C) of life in the world. A gigaton is equal to a billion metric tons. A metric ton is 1,000 kilograms, or about 2,200 pounds.

Of life’s ‘kingdoms’ there are the protists (like amoebae), archaea (single-celled organisms somewhat similar to bacteria), fungi (mushrooms and other types of fungus), bacteria, plants, and animals. The protists are estimated to weigh 4 GT C, archaea 7 GT C, fungi 12 GT C and bacteria 70 GT C. At the other end of the scale plant life weighs in at a huge 450 GT C.

All animal life weighs in at 2 GT C and, of that, humans are 0.06 GT C. Arthropods (insects) outweigh us by a factor of 17 at 1 GT C. The fish and the molluscs weigh more at 0.7 and 0.2 GT C respectively.