Pennsylvanian 323.2 Mya - Second half of “Carboniferous” named for the numerous coal beds found across the state.

• COAL - Growth of Geology

  • The usefulness of coal as a source of energy was discovered as early as 4000 BC in China. It was burned to create heat in stoves and furnaces. By 1000 BC it was being used to smelt Copper. At the end of the 13th Century Marco Polo visited China and was amazed by the amount of “black rock” being used by the people providing luxuries such as three hot baths per week. It had been known in Europe for smelting and heating the water used in the roman baths, but it was difficult to mine and wood for charcoal was abundant.

  • All of this changed with the onset of the industrial revolution and the huge demand for energy in the mid 1700s. As steam engines grew larger, waterwheels and wood burning furnaces couldn’t keep up. Large scale coal mining spread throughout the UK in southern Wales, northern England and southern Scotland. In the US, western Pennsylvania and West Virginia along with other regions surrounding the Appalachians became major coal producing areas.

  • The huge demand for coal lead to widespread study of coal bearing units including the first cross-section illustrating a sequence or repeating coal seams, their thickness, the dip of the beds and how they project further in 3D. This gave him the ability to predict where the seams would be along with their thickness. John Strachey’s cross-section was the first.

• TREES, FERNS AND SWAMPS

  • Up to this point in geologic history plants were fairly small, but by the Pennsylvanian the landscape was quickly dominated by gigantic fern trees, horsetails and dense forests of ferns. The shallow seas receded leaving vast deltas, swamps and floodplains across the clustering continents.

  • Modern trees are quickly decomposed by bugs like termites and organisms that consume the organic matter to use at fuel. But back in the Pennsylvanian there was nothing to break down the huge amount of plant material. Instead, dead trees and ferns piled up over millions of years leaving enormous volumes of organic matter. Sediments from the newly growing mountain chains buried and compacted the organic matter encasing them in sediment and preserving them.

  • The organic matter came in the form of trapped carbon. Trees take in carbon dioxide from the atmosphere and release oxygen. In modern times, when a tree degrades the carbon is released back into the atmosphere in the form of Carbon Dioxide, but since this plant matter never decomposed, many tons of carbon in the form of CO2 was taken out of the Pennsylvanian atmosphere via photosynthesis. When the plants died that carbon remained trapped within the structure of the plants. Once the material was buried, it remained trapped.

• CYCLOTHEMS

  • The CO2 that modern humans are releasing into the atmosphere is causing our climate to warm as a result the amount of ice and snow trapped on land is reducing causing an increase in sea level. The rocks of the Pennsylvanian indicate this process occurred repeatedly. As CO2 was removed and trapped in plant material buried under sediments, the atmosphere cooled, widespread glaciation occurred and sea level dropped exposing Mississippian limestones made of CaCO3 which released more CO2 into the atmosphere causing the climate to warm and sea level to rise. This process results in a cycle of repeating patterns of deposition representing the cycles of high sea level and low sea level.