From The Living Biosphere To Transformed Carbon

Coal

Coal is a carbon-rich combustible sedimentary rock formed principally from accumulated plant material that has undergone physical and chemical transformation. It is not simply compressed wood. During transformation, plant-derived material loses water and volatile constituents and is reorganized into progressively more carbon-rich material. Yet coal can retain spores, roots, bark, wood, cuticle and other recognizable botanical structures. Its biological starting material is therefore not merely inferred; portions of it remain physically identifiable.

Coalification

Coalification is the physical and chemical transformation of accumulated plant material into progressively more transformed coal. The commonly described sequence is plant material to peat, lignite, subbituminous coal, bituminous coal and anthracite. Peat is partially decomposed plant material accumulated where environmental conditions limit complete destruction. Lignite is relatively low-rank coal. Bituminous coal is more strongly transformed, and anthracite represents a high-rank, carbon-rich state with comparatively low volatile matter.

Coal Rank

Coal rank describes the degree of coalification: the physical and chemical state reached by the material. Rank is determined from measurable properties such as moisture, volatile matter, carbon content, calorific behavior and optical changes in organic components. Rank therefore describes transformation; it is not, by definition, a measurement of elapsed time.

Vitrinite and Vitrinite Reflectance

A maceral is an identifiable organic component of coal, somewhat analogous to a mineral being an identifiable component of ordinary rock. Vitrinite is a major maceral derived principally from plant tissues. Vitrinite reflectance measures how strongly polished vitrinite reflects light under standardized microscope conditions. Reflectance generally rises as coal undergoes increasing thermal alteration and is therefore widely used as a measure of coal rank and thermal maturity.

Laboratory Zero

The Living Biosphere

Before coal existed underground, its carbon participated in a living terrestrial biosphere. Pennsylvanian coal contains identifiable remains of giant lycopsids such as Lepidodendron and Sigillaria, together with tree ferns and other vegetation. These giant lycopsids were not true ferns; they were tree-sized relatives of modern club mosses, some exceeding approximately 30 meters or 100 feet, in height.

The great giant-lycopsid coal systems were concentrated within broad tropical wetland provinces. Other coal provinces contain different vegetation. Gondwanan coals, for example, preserve a distinct Glossopteris flora associated with more seasonal environments. Coal therefore preserves not only biological material but information about the environment in which that biological material grew.

The biological inventory was enormous. Compaction measurements indicate that finished bituminous coal can represent roughly an order of magnitude more precursor peat thickness, with measured ratios varying substantially by material and deposit. An eight-foot coal seam can therefore represent many tens of feet of precursor peat. That does not mean the entire reconstructed peat column existed uncompacted at one instant; it establishes the magnitude of biological production and accumulation represented by the finished seam.

Burial and Preservation

Coal-bearing strata preserve both rooted vegetation and rapid sedimentary interruptions. Upright trunks and attached rooting systems demonstrate that portions of the vegetation grew where they are now preserved. Flood deposits, mudstones, sandstones and abrupt burial surfaces demonstrate that sediment could also arrive rapidly and terminate existing biological environments.

The evidence therefore does not require a choice between all vegetation growing in place and all vegetation being transported catastrophically. Natural coal systems preserve biological production, peat accumulation, episodic sedimentation, burial and environmental change. These processes must be distinguished rather than collapsed into one clock.

Laboratory One

Human Experimental Coalification

Controlled experiments demonstrate directly that peat, wood, lignite and natural low-rank coal can undergo substantial coalification on human experimental clocks when appropriate conditions are supplied.

In one USGS experiment, actual Indonesian peat and peatified wood were subjected to approximately 125 degrees Celsius, about 408 atmospheres of lithostatic pressure, about 177 atmospheres of fluid pressure and controlled removal of reaction products for 75 days. The resulting chemical and molecular changes became broadly comparable with naturally coalified material from the same region.

Other experiments heated peat, brown coal and subbituminous coal for 48 hours over progressively higher temperatures. At sufficiently elevated experimental temperatures, peat and brown coal reached vitrinite-reflectance values associated with anthracite-stage transformation. More recent hydrous-pyrolysis experiments have measured substantial rank and structural changes in natural coal within 24 hours.

These experiments do not establish that natural anthracite formed in one or two days. Their temperatures and boundary conditions intentionally accelerate the reactions. They establish the narrower and more important result that coal-rank transformation does not possess an experimentally demonstrated intrinsic requirement for millions of years.

The Whole Environment Again

Coalification, like petroleum generation, responds to the whole physical environment. Temperature strongly changes reaction rate. Pressure affects fluid state and organic maturation and can suppress one stage while promoting another under different conditions. Water and other fluids alter chemical pathways. Confinement changes escape and retention of reaction products. Starting composition matters.

The laboratory therefore does not demonstrate coal plus time. It demonstrates material responding to an imposed combination of temperature, pressure, fluids, confinement, chemistry and sequence while a clock records the interval.

Laboratory Two

Pennsylvania

Pennsylvania provides an unusually clear natural comparison. Pennsylvanian coal-bearing rocks across the Appalachian Basin display a major rank gradient. Western portions contain predominantly bituminous coal, while eastern Pennsylvania contains anthracite and meta-anthracite. Measured vitrinite reflectance rises substantially from west to east.

The higher-rank eastern coal occurs in a geological environment characterized by greater deformation, folding and faulting, altered burial and thermal histories and evidence of fluid movement associated with Appalachian mountain building. Burial alone does not explain every part of the rank pattern; elevated heat flow and hot-fluid activity have also been investigated as contributors.

Thus Earth supplies naturally the same classes of variables that Laboratory One demonstrates can transform organic material: burial and confinement, temperature, pressure and loading, fluids, chemistry and deformation. The finished coal records the resulting state.

Coal Rank is a State,
Not a Stopwatch

The Pennsylvania comparison makes the central distinction visible. Coal of related geological setting can occupy very different ranks where its subsequent physical environment differs. The rank tells us what happened to the material. By itself, it does not tell us how long the transformation required.

Natural histories may independently constrain duration through stratigraphy, dating, burial reconstruction, thermal modeling or other evidence. Those measurements should be evaluated on their own terms. They must not be confused with the rank measurement itself.

Three Laboratories

Domain 7 therefore contains three laboratories. Laboratory Zero is the living biosphere, which produced the vegetation and biological carbon. Laboratory One is the human experiment, where known organic material is subjected to measured conditions and the transformation clock is directly observed. Laboratory Two is Earth, where the biological inventory has been buried and transformed at enormous scale.

The three laboratories answer different questions. The biosphere identifies the starting material. The human experiment identifies what physical conditions can transform it and how rapidly transformation can occur under those conditions. Earth demonstrates that comparable classes of conditions exist naturally and contains the completed coalification products.

Three Clocks

The evidence also requires three clocks to remain separate: the production and accumulation of vegetation and peat; the burial and environmental transition of that material; and the subsequent coalification and rank transformation. A duration assigned to one of these processes must not automatically be transferred to the others.

Domain 7 Finding

Coal is transformed biological material. Its botanical remains identify an earlier terrestrial biosphere, while its rank records subsequent physical and chemical transformation.

Laboratory experiments demonstrate that substantial coalification and rank changes can occur on clocks measured in hours, days and months when appropriate temperature, pressure, fluid, confinement and chemical conditions are supplied. Pennsylvania’s natural coal fields demonstrate that Earth supplies these classes of conditions and that coal rank changes systematically where the physical history changes.

Coal rank is therefore a measurement of transformed state, not a stopwatch. Laboratory One demonstrates that the transformation mechanism can operate rapidly under suitable conditions. Laboratory Two demonstrates that Earth supplies the mechanism at regional scale. The duration of any particular natural coal-forming history must be established independently rather than inferred merely from the existence or rank of the finished coal.

Laboratory Zero produces the biological inventory. Laboratory One reveals what matter can do. Laboratory Two displays what Earth has done.

Research Record

Key comparisons used in this investigation include experimental early-stage coalification of natural peat and peatified wood under controlled temperature, lithostatic pressure, fluid pressure and reaction-product removal; rapid thermal and hydrous-pyrolysis experiments on peat, lignite, brown coal, subbituminous coal, and natural coal; experimental studies of pressure, water and temperature effects on vitrinite maturation; botanical identification of giant lycopsids, tree ferns, and other plants within Pennsylvanian coal; measured peat-to-coal compaction; rooted fossil forests and rapid sedimentary burial surfaces associated with coal measures; and the natural bituminous-to-anthracite rank gradient across the Appalachian Basin and Pennsylvania.

Produced by The Lilborn Equation Team:

Michael Lilborn-Williams

Thomas Jackson Barnard

Audrey Williams