Sunday, July 1, 2018

The Weight of Life Presented in a Tower

Image result for taxa

Environmental & Science Education
Edward Hessler

A census by Yinon Bar-On, Rob Phillips, and Ron Milo that sorted all life on earth by weight in gigatons of carbon was reported in the Proceedings of the National Academy of Sciences (PNAS).

The authors note that they use biomass as a measure of abundance, which allows us to compare taxa whose members are of very different sizes. Biomass is also a useful metric for quantifying stocks of elements sequestered in living organisms. We report biomass using the mass of carbon, as this measure is independent of water content and has been used extensively in the literature.

Over at Vox, Brian Resnick and Javier Zarracina used these data to help us visualize the impressive numbers. They present the data in what they describe as a kind of tower of weight. You may recall pyramids of biomass from a biology or ecology course. The tower visual has a different purpose. It is, in the words of the PNAS authors, a global, quantitative view of how the biomass of different taxa compare with one another.

Taxa are populations of organisms that form a unit. In the case of this paper think of them as broad kingdoms of organisms. Resnick and Zarracina explain this very nicely. There are the protists (think microscopic life like amoebae), archaea (single-celled organisms somewhat similar to bacteria), fungi (mushrooms and other types of fungus), bacteria (you’re familiar with these, right?), plants, and animals.

First, a definition. A gigaton is equal to a billion metric tons. A metric ton is equal to a 1000 kilograms or about 2200 pounds. As you can see these numbers add up into some very large numbers.

Of course the census is not perfect and the authors of the original paper discuss various deficiencies. It also makes you think about what life is missing, especially as humans have come to dominate the planet.

The chart and the article by Resnick and Zarracina are found here.

h/t 3QuarksDaily

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