Is value of mass of all living things on Earth constant, growing or decreasing?
How was it evolving over planet’s lifetime? Would graph of this value be fairly linear or would it consist more complex patterns?
I believe this is not fully understood but I am not an expert. All Plants on earth put together and all microbes on earth put together - have almost the same amount of carbon - cite
No, I don’t think biomass would be constant. I also don’t think you can assign any long-term trend to it. It’s a response to environment and to the capability of the species.
For one example, an enormous amount of the total biomass is tied up in trees. If woody trees all went extinct and Earth was taken over by grass, ferns and shrubs, there’s simply no way to replace all that biomass. It used to be stored vertically and now there’s nothing capable of growing tall enough to replace it.
As another example, an ice age would change the amount of land available for life. In terms of recent ice ages, I’m not sure whether this would be a net positive (since you’d have lower oceans and more beach-front land) or a net negative (since you’d cover half of the northern continents in ice). Taken to the extreme of the snowball Earth period in our way-back history, there’s no doubt that total biomass would be reduced.
Does not the existence of massive chalk, marble, and limestone deposits mean that biomass must have decreased as carbon is removed from the biosphere?
You might only mean on a longer time-scale, but it’s worth calling out that there are seasonal effects, too. As the northern hemisphere’s winter kicks in, trees lose their leaves and annuals die off and decay. This is not compensated for by the southern hemisphere’s summer, since it has less land area. You can see this in the saw-tooth pattern in CO2 measurements - as the biomass decreases in the winter months, CO2 increases by a couple ppms.
Carbon is also added from a number of geologic sources, including volcanism and decomposition of the same rocks that you mention. There’s a carbon cycle on both a biological scale and a geological one.
As a trivial example to prove that it’s not constant, before abiogenesis happened, total biomass was zero. Now it’s more than zero.
Well, obviously it wasn’t always the same but after some time it may have reached some point, call it optimum and just oscillate around that value without any major further progression…
… until we hit another ice age, or iceball-earth age …
Given that those extremes exist, I doubt that it’s a constant in general, just less variation for narrower climactic ranges.
Does sequestered carbon in fossil fuel deposits count as biomass?
No. Biomass is defined as coming from living or recently living organisms. A key distinction here is that biomass is considered to be part of the active carbon cycle, while fossil fuel is not. The very fact that the carbon has been sequestered for hundreds of millions of years and essentially permanently taken out of the carbon cycle is precisely the problem with rapidly re-introducing it back into the system. It’s like we’re frantically trying to return the climate to that of the Cretaceous within a couple of centuries and going, “what could possibly go wrong?”
Wikipedia’s page is interesting. Apparently “dry biomass” counts only carbon. Since “Most of this biomass is found on land, with only [1 to 2%] found in the oceans”, presumably the emergence of life on land had a big effect.
Wikipedia’s estimate of total dry biomass (560 billion tonnes) excludes bacteria, but “… the total live biomass of (the estimated 5 nonillion) bacteria may exceed that of plants and animals.”
I think that would be true for a stable geologic period. If the climate stays consistent and there’s no major shift in the life forms themselves, you would expect everything else to be pretty consistent.
Really, the way I see it, the upper limit on biomass is based on sunlight, photosynthetic efficiency and energy loss at each trophic layer. Right now, we have (very simplified) 30% of the Earth with land, and 3% of land sunlight captured by plants. So only 1% of sunlight is growing plants, which support herbivores with 10% of their biomass, and herbivores support tier 1 carnivores at 10% of their mass, with tier 2 carnivores at 10% of that. So you could change any step in that equation to alter the potential biomass.
Unlike fossil fuels, that carbon wasn’t part of the living organism before it was deposited - it was just extracted from solution as carbonate ions (when it wasn’t just precipitated on its own). It isn’t counted as biomass - bones, shells, reefs etc generally aren’t.
So is the actual trend unknown? Or just no one here have an answer?
It seems that forests make up the bulk of Earth’s biomass (when bacteria are excluded). 80% of Earth’s forests have been destroyed or degraded recently (though there is some regrowth). This would imply that there has been a very significant reduction in total biomass just over the past century, no?