Amount of Carbon in the biosphere?

Question

Wondered if anyone had details on the amount of carbon currently in the biosphere vs. what is stored in the form of underground hydrocarbons.

I'm asking the question because I'm wondering how much more biomass was on the earth at one point in time

Additionally does anyone know of theories as to why that biomass was lost and stored underground and not still active on the plantet's surface?

Is this trend continuing......will we reach a point far in the future when there is no free carbon on the surface? Will whatever made previous carbon be sequestered happen again?

Just curious and looking for some answers

Answer 1

Planetary biomass has been largely constant at around 1,900 gigatonnes (10^9) over the past few millions of years.

Hydrocarbons (proven reserves remaining, back of envelope calculations)):

Coal - 1 trillion tonnes

Oil - 150 billion tonnes

Gas - 160 million tonnes

Total hydrocarbons, approximately  1.2 trillion tonnes

Total biomass, approximately 1.9 trillion tonnes

The different mechanisms of how biomass gets stored in long term reservoirs are quite well known (but too many/long to get into here) but in general it means sea organisms and organic particles washed into the sea settling to the bottom and plant and animal matter on land dying and decaying on the ground slowly being covered by wind-blown sediments and/or more decaying matter.

It isn't "lost", this is a natural long-term cycle of carbon.

Without human extraction (and only a small percentage of dead biomass becomes useful to humans), this sequestered carbon would eventually be returned to surface and atmospheric carbon by geological forces (basically plate tectonics leading either to erosion or subsuming into magma and then ejected out via lava).

The whole cycle is largely in equilibrium thus there are no forecasts that I know of (until the end of the useful life of the Sun) saying that carbon would disappear from the surface... of course, that's a long time and some new things may happen in the next four billion years!

Answer 2

Not all biomass is converted to fossil fuels.