Hacker News Reader

But not necessarily released as CO2, which is what "re-emitted" means to me. If it goes atmosphere -> tree -> fungus -> bits of fungus buried in the ground for millions of years, that's effective sequestration.

It may well be, but that's not what happens to most of the wood in trees— most of it rots (CO2 released slowly by the organisms consuming the wood) or burns (CO2 released by combustion).

This is true only in part.

We have found shells, made of Calcium carbonate, still relatively intact more than 3000 years after the death of the animal. Some shells had last for 500000 years (See Nature 2014-dec-03)

Under the sea there are entire ecosystems based in dead shells.

As said below, it's not C, but CO2 we were worried about. Also I admit that I don't know if humus organism produce CO2 from wood remains.