Is it today, due to the advent of mechanized agriculture and irrigation? Was it a long time ago because of huge fuckin’ dinosaurs? Has it held relatively constant due to limitations on carbon/nutrients/solar input/etc?
Curious minds (mostly mine) want to know.
It was probably during the Cretaceous, which was a “supergreenhouse” period when the level of carbon dioxide was four or five times what it is today and global temperatures were much higher. Oxygen was also about 50% higher than current levels.
High CO2 and high temperatures would have promoted high plant productivity. In turn, such high productivity may have allowed dinosaurs to become as big as they did, since herbivores would have been able to find enough food in a relatively smaller area than today. (And carnivores could have gotten bigger because they had bigger herbivores to prey on.) Thick coal beds in some areas also suggest high plant productivity.
Maybe the carboniferous.
What’s your reasoning, other than the presence of extensive coal beds? Global CO2 and temperatures were lower than in the Cretaceous, so that plant productivity was probably lower.
Is the total biomass on the planet limited by the amount of carbon available in the biosphere? Where does all the carbon that sloshes around between living organisms come from in the first place, anyway? Out of rocks? Or out of CO2 in the pre-biotic atmosphere?
What determines the amount of biomass anyway? Is it relatively constant for given atmospheric and/or soil conditions? Does every new human born displace an equivalent amount of living plant/animal matter?
Most biomass currently is microbial. I don’t know that looking at the size of land animals would say much about the past levels. Plant matter… I’m not too sure. I’d take a look at when deep water shales and coral reefs were laid down.
I may be misremembering the origins of deep ocean shale… Still, the answer’s in sediment. I don’t know how to determine the past levels of bacteria and archea there. Methane levels?