How do you arrive at carboniferous calamite trees fossils, with stems complete with what appears to be perfectly preserved leaves, From vegetation that grew in hot steamy swamps.
Surely the stems and leaves would rotted and been eaten by bacteria long before they would have had a chance to fossilize and then turn into coal.
One answer for this would be that many untold numbers of trees where uprooted and instantly buried, then compressed and eventually became layers of coal. These layers are sometimes hundreds of feet deep and unsullied by other material.
Let me answer this;
The coalification process involves several steps but basically boils down to the vegetation falling into a standing body of water or otherwise being protected from oxidizing conditions.
Generally the possible fates of organic carbon (plant material are) in the environment are:
1. Exposure to atmospheric oxygen (it just decays away into CO2 and H2O and some other gunk, not much left for us to look at)
2. Restricted contact with atmospheric oxygen (rotting, mouldering and humification)
3. Immediate submersion (Peatification)
4. Immersion into a strongly reducing environment (Putrefaction)
(
SOURCE)
What it amounts to, generally speaking, is that we can find instances where either limited biological activity occurs on the plant remains and/or oxygen is kept away from them, but ultimately we wind up with something that is
depleted in hydrogen and oxygen, and
enriched in carbon.
No magic there. Just the stuff that makes up plants.
WHen you look at coal under a microscope you actually often see what looks like almost "intact" plant tissue!
In reality these are "appearances". The features of the original plant
cells are still there, the cell walls are very much present, and sometimes you can even see the original pores in some of the cell walls! It's amazing. But in reality the
chemistry of these materials is greatly changed.
The cellulose is often removed or so altered as to not be recognized as cellulose. The lignin, which is much more resiliant chemically, is itself quite altered. During this and after the initial processes the coal is buried deeper and heated up, which can cause additional changes.
This is a representation of lignin:
This is what is left over after some amount of coalification (representative only, not a "coal molecule", but an estimation of the types of chemical compounds left):
Keep driving off oxygen and hydrogen and you wind up with Anthracite which chemically looks
kinda like this:
We can look at the chemistry of these cell walls and we can actually back track the kind of chemical processes that probably occurred to make them the way they are.
And none of it
necessarily requires some enormous catastrophe. What it does require is, perhaps, a rather rapid burial (but not catastrophically so), or at least some way of sequestering it from atmospheric oxygen. We can see that every single day even today in swampy standing water that has little circulation. And some deeper burial in the geologic column and gradual heating.
We can find the kind of bacteria that can live in reducing environments that can alter materials to make coal. We know a great deal about the heat necessary to alter organic matter in the geologic environment.
So when you look at preserved leaf in a coal seam it is like looking at an impression. You see a leaf, indeed, but what you are looking at has been amazingly chemically altered. But its "form" remained. And the chemistry around how it got from point A to point B to point C is reasonably well know.
Coal geochemistry is very interesting. Coal petrology (the field where you look at the coal itself, usually under a microscope) is one of the most fascinating areas of geology I can think of. There's a LOT to learn from coal. It's complex but understandable.
