Environmentalists often say that humanity needs to shrink its planetary footprint. Now, a new study has demonstrated how literally massive that footprint is.

While the mass of Earth’s life forms stands at about 1.1 trillion metric tons (1.2 trillion U.S. tons) and has not changed much in recent years, the so-called “anthropogenic mass” of artificial materials is growing exponentially. The mass of everything people have built and made, from concrete pavements and glass-and-metal skyscrapers to plastic bottles, clothes, and computers, is now roughly equal to the mass of living things on Earth and could surpass that this year, according to research published today in Nature.

The finding may bolster the argument that Earth has entered the Anthropocene, a proposed geologic