terça-feira, 22 de maio de 2018

Michael Hanson/Aurora Photos

Plants outweigh all other life on Earth

As plantas superam todas as outras formas de vida na Terra

Plants pack more heft than any other kingdom of life on the planet, making up 80% of all the carbon stored in living creatures. That’s just one surprise in a comprehensive new survey of Earth’s biomass, which finds that groups with the greatest number of species—such as arthropods—aren’t necessarily the heaviest.


Measured in terms of carbon content (to factor out variable components like water), all life on Earth weighs about 550 gigatons. Of that, plants make up 450 gigatons of carbon (GT C), followed by bacteria at 70 GT C and fungi at 12 GT C, scientists report today in the Proceedings of the National Academy of Sciences. Animals comprise a mere 2 GT C, of which half are arthropods—including insects, spiders, and crustaceans. And although humans weigh in at just 0.06 GT C—on par with krill and termites—our impact on biomass since the beginning of civilization has been huge, scientists say. Humans and their cattle, pigs, and other livestock outweigh wild mammals by more than 20-fold; similarly, domesticated fowl surpass all other birds. Humans have also had an impact on plant biomass, which has been cut in half in the past 10,000 years.

To figure out the biomass of each creature, quantitative biologists spent 3 years combing the scientific literature. But their ultimate goal wasn’t to figure out how much life weighs—it was to discover the most abundant protein on the planet. They’re still working on that question (subsurface microbes presented them with a particular challenge), but they hope to answer it within the coming year.


Medida em termos de conteúdo de carbono (para fatorar componentes variáveis ​​como água), toda a vida na Terra pesa cerca de 550 gigatoneladas. Dessas, as plantas compõem 450 gigatoneladas de carbono (GT C), seguidas de bactérias a 70 GT C e fungos a 12 GT C, relatam cientistas na revista Proceedings, da Academia Nacional de Ciências. 

Os animais compreendem apenas 2 GT C, dos quais metade são artrópodes - incluindo insetos, aranhas e crustáceos. E, embora os seres humanos pesem apenas 0,06 GT C - a par com o krill e cupins - o nosso impacto na biomassa desde o início da civilização tem sido enorme, dizem os cientistas. Os seres humanos e seu gado, porcos e outros animais superam os mamíferos selvagens em mais de 20 vezes; da mesma forma, aves domésticas superam todas as outras aves. Os seres humanos também tiveram um impacto na biomassa vegetal, que foi reduzida pela metade nos últimos 10.000 anos.


Para descobrir a biomassa de cada criatura, os biólogos quantitativos passaram três anos vasculhando a literatura científica. Mas seu objetivo final não era descobrir o quanto a vida pesa - era descobrir a proteína mais abundante do planeta. Eles ainda estão trabalhando nessa questão (micróbios subsuperficiais apresentaram-lhes um desafio particular), mas esperam respondê-lo no próximo ano
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Posted in:
doi:10.1126/science.aau2463

Elizabeth Pennisi

Liz is a senior correspondent covering many aspects of biology for Science.