Whether it's the build-up of microplastics in the Arctic or the coming of the sixth extinction, it's clear humanity has left an indelible mark on the planet – so much so that many scientists are calling the current geological period the Anthropocene (literally meaning human-cene). Yet, did you know, if you were to take the global population (all 7.6 billion of us) and put it on a giant scale, it would only make up 0.01 percent of the combined mass of all living things?
That's according to a study published in the Proceedings of the National Academy of Sciences (PNAS) this week, which has calculated the Earth's biomass distribution using hundreds of recent studies and newly made estimates where data was missing.
"It’s what you could call a meta-meta-analysis,” Ron Milo, associate professor at the Weizmann Institute of Science, told New Scientist. "It’s based on hundreds and hundreds of papers. We also consulted with many, many experts.”
Based on the authors' estimations, the world's total biomass is 550 gigatons of carbon (Gt C) – the vast majority (82 percent) of which is plant life. Bacteria make up another 13 percent, and the remaining 5 percent is a hodgepodge of animals, insects, and fungi.
To put into perspective how minuscule humanity's presence is (at least, in terms of sheer weight), consider this: the Guardian calculated that viruses weigh three times as much as we do, fish 12 times, and plants 7,500 times.
"The fact that the biomass of fungi exceeds that of all animals sort of puts us in our place," James Hanken, an evolutionary biology professor at Harvard University, told Associated Press. If you were to pit humanity's mass against fungi, it would outnumber us on a scale of 200 to one.
Yet, Homo sapiens' impact on the planet has been vast. According to the Guardian's calculations, the study also estimates that 83 percent of wild mammals and 50 percent of plants have been destroyed since the arrival of modern humans around 200,000 years ago. Meanwhile, livestock numbers have mushroomed – 70 percent of birds are farmed poultry and 60 percent of mammals are farmed. Thirty-six percent of the remaining mammals are human, which means just 4 percent are wild animals.
The authors also worked out where the Earth's biomass was distributed and found that almost all animal mass is in the ocean (of which, 70 percent are microbes) and almost all plant life is land-based. Roughly 13 percent of life – mainly bacteria – lives deep under the Earth's surface.
However, it is worth pointing out that this is an estimate and there are uncertainties around the numbers picked out in the study, particularly for little-studied or hard-to-study taxa or geographies such as viruses and the deep ocean. As Vaclav Smil from the University of Manitoba in Winnipeg, Manitoba, told New Scientist, we can't even accurately calculate figures for the total biomass of elephants.
