60% of all mammals on Earth are livestock.
Photograph: Daniel Beltra/Greenpeace
reveals humanity's surprisingly tiny part in it
as well as our disproportionate impact
Yet since the dawn of
humanity has caused the loss of 83% of all wild mammals and half of
plants, while livestock kept by humans abounds.
Another surprise is that the teeming life revealed in the oceans by the recent BBC television series Blue Planet II turns out to represent just 1% of all biomass.
The vast majority of life is land-based and a large chunk - an eighth - is bacteria buried deep below the surface.
The transformation of the planet by human activity has led scientists to the brink of declaring a new geological era:
One suggested marker for this change are the bones of the domestic chicken, now ubiquitous across the globe. The new work reveals that farmed poultry today makes up 70% of all birds on the planet, with just 30% being wild.
The picture is even more stark for mammals:
The destruction of wild habitat for farming, logging and development has resulted in the start of what many scientists consider the sixth mass extinction of life to occur in the Earth's four billion year history.
half the Earth's animals are
thought to have been lost in the
last 50 years.
But comparison of the new estimates with those for the time before humans became farmers and the industrial revolution began reveal the full extent of the huge decline.
Just one-sixth of wild mammals, from mice to elephants, remain, surprising even the scientists.
In the oceans, three centuries of whaling has left just a fifth of marine mammals in the oceans.
Despite humanity's supremacy, in weight terms Homo sapiens is puny.
Viruses alone have a combined weight three times that of humans, as do worms. Fish are 12 times greater than people and fungi 200 times as large.
Source: Proceedings of the National Academy of Sciences
of the United States of America
But our impact on the natural world remains immense, said Ron Milo, particularly in what we choose to eat:
The researchers calculated the biomass estimates using data from hundreds of studies, which often used modern techniques, such as satellite remote sensing that can scan great areas, and gene sequencing that can unravel the myriad organisms in the microscopic world.
They started by assessing the biomass of a class of organisms and then they determined which environments such life could live in across the world to create a global total.
They used carbon as the key measure and found all life contains 550bn tons of the element.
The researchers acknowledge that substantial uncertainties remain in particular estimates, especially for bacteria deep underground, but say the work presents a useful overview.
Paul Falkowski, at Rutgers University in the US and not part of the research team, said: