What is the weight of all living things?
Or what happens when scientists ask really big questions
I know all of you have a lot on your mind (as do I). I’m going to sidestep of the stuff constantly in the news this week to provide you with something completely different for a few minutes.
When you and I were very young we were all filled with curiosity. We asked a lot of profound questions. And adults— whether they were teachers or parents— told us to focus on reading our textbooks and getting good grades. We got older and became self-conscious. We became more worried about asking a bad question and making a fool of ourselves. Curiosity took a back seat.
If you have a small child (or have been near one) you will notice that every generation of snot-nosed kids possesses this uncanny ability to ask the most profound and basic questions. Where was I long before I was born? What happens when people die? Why are people ticklish? How does a fish feel when the shark bites it? If it hurts, then why DOES the shark bite it? Why do people look different? Where did the moon come from? Why does the sun set if the earth is moving? Why does the belly button look so silly?
These are annoying questions, but they are not cynical and useless questions like the one the interviewer in Satyajit Ray’s Jana Aranya asks the protagonist- What is the weight of the moon?
Kids ask the best questions. And I bring this up as a rather convoluted way of getting at what science really is about. Science happens when someone asks a question and tries to find out the answer. Scientists ask a lot of questions, but most of the questions asked are incremental and predictable. There’s no harm in that: this is how papers get published, projects get funded, and people get degrees.
But once in a while it is awesome to come across scientists trying to answer a really big question in a systematic way. Like this one…
How much is the total biomass (as a proxy for weight) of different kinds of life?
I sort of stumbled across this fantastic paper published in a prestigious journal while doing some research of my own. Three scientists (two at Weizmann Institute of Science in Israel and one at Caltech in the US) did comprehensive breakdown of the biomass of all life on Earth.
I’m going to gloss over the methodology, but it’s in the paper (and they go over not only how to calculate biomass, but also the uncertainty in the numbers; for example, they assume that an average human weighs 50 kilograms). The units they use are gigatons of carbon, with 1 Gt C = 10^15 g of carbon (and one of the reasons they measured carbon is to avoid water. As anyone dieting painfully knowns, most of life is water-weight).
Here’s what they found:
The total biomass of the earth is around 550 gigatons of carbon (Gt C) distributed across all of life (and some nonliving entities like viruses), but…
Terrestrial plants make up 80% of the biomass of the Earth. We are well and truly a green planet.
Unlike plants most of animal biomass— nearly 70%— is found in the ocean. The land belongs to plants, and the ocean belongs to animals.
Bacteria are massive in number but small, so they’re only 15% of the biomass. There may be ten times as many viruses as bacteria but they’re even smaller, so they hardly figure at all in the weight of things.
People and livestock outweigh wild mammals by a ratio of 20 to 1. The total weight of chickens on the planet is three times the weight of all wild birds.
Before people arrived on the planet, the biomass was twice what it is today. Wild mammal biomass is one-sixth of what it was before people. We’ve cut down trees and killed most wild animals (either directly or through habitat change).
Producers (such as trees that photosynthesize) make up most of land. On the other hand consumers (animals and microorganisms) make up most of the oceans. There’s 80 times more biomass on land than in oceans.
The oceans cover the planet but marine water is relatively nutrient poor compared to land. Why is that? It has to do with the poor penetration of light in water. Photosynthetic plants need light. The sun is the source of most of our energy.
This is an interesting paper, but it’s not solely an academic observation. As we deal with challenges in sustainability, climate change, and habitat destruction, an analysis such as this helps to look at the forest as well as the trees.
As one of the authors of the paper put it:
I was struck when I realized how much of the living world we have already depleted and lost. In the puzzles of big animals that I do with my daughters, there is usually an elephant next to a giraffe and a rhino. But in real life, there is now a cow next to a cow next to another cow and then a chicken. I think we should reconsider how much we consume and what we want to protect before it will be too late.
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Postscript: Most of you are (I hope) familiar with the fantastic webcomic xkcd. The creator, physicist Randall Munroe wrote a great book that I have to recommend in ending today called What If? Serious Scientific Answers to Absurd Hypothetical Questions. This is a book that dares to take on some of the questions you didn’t know anyone wanted answered.
What else I’m reading this week:
There’s a secret language in China that only women know.
It helped them to cope with social and domestic hardships.
Women who created this strong bond were known as “sworn sisters” and were typically a group of three or four young, non-related women who would pledge friendship by writing letters and singing songs in Nüshu to each other. While being forced to remain subservient to the males in their families, the sworn sisters would find solace in each other’s company.
Noise pollution increases susceptibility to disease… in fish!
This one is a doozy.
Here, we investigated the impact of acute and chronic noise on vertebrate susceptibility to parasitic infections, using a model host–parasite system (guppy–Gyrodactylus turnbulli). Hosts experiencing acute noise suffered significantly increased parasite burden compared with those in no noise treatments.
Now is not the best time ever.
Taking a very optimistic view of human life (and the general argument that a mammalian species exists for around 1 million years), this journalist believes that the best 50,000 years of human existence are yet to come. It’s a great essay that considers both sides of the argument.
The link for the hardcover “COVID-19: Separating Fact from Fiction” is now available on Amazon’s Indian site.
That’s it for this week. If you like this post, please share it.
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