Question

Suppose that a 4-m layer of plant matter was compacted to form a coal layer \(1 \mathrm{~m}\) thick. By what percent has the thickness of organic material been reduced?

Short answer

The thickness has been reduced by 75%.

Step-by-step solution

Understanding the Problem

We begin by identifying the initial and final thicknesses of the material. Initially, we had a 4-meter layer of plant matter which was compacted into a 1-meter coal layer.

Setting Up the Formula

To find the percentage reduction in thickness, we use the formula for percentage decrease: \[\text{Percentage Decrease} = \left(\frac{\text{Original Thickness} - \text{New Thickness}}{\text{Original Thickness}}\right) \times 100\]Where the original thickness is 4 meters and the new thickness is 1 meter.

Calculating the Percentage Decrease

Substitute the values into the formula: \[\text{Percentage Decrease} = \left(\frac{4 - 1}{4}\right) \times 100\]Simplify the expression inside the parentheses:\[\text{Percentage Decrease} = \left(\frac{3}{4}\right) \times 100\]This gives:\[\text{Percentage Decrease} = 0.75 \times 100 = 75\%\]

Conclusion

The thickness of the organic material has been reduced by 75%.

Key concepts

Compaction

Compaction is a process often observed in geological formations where layers of material, such as sediment, are pressed and consolidated under pressure over time. This process can significantly alter the physical properties of the material involved.
For example, as layers of plant matter accumulate, they undergo compaction due to the weight of the overlying layers. The increased pressure compacts the material, decreasing its volume and thickness.
The degree of compaction directly influences the density of the material. As the material reduces in thickness, its particles are pushed closer together, eliminating voids and increasing density. This is essential in the transition of plant material into other forms, such as coal during coal formation.

Organic Material

Organic material refers to the remains of plant or animal matter. In the context of coal formation, this is typically plant debris.
This material is rich in carbon and other elements that are gradually transformed into coal through geological processes.
Initially, a thick layer of plant matter provides the organic material needed for coal production. Over time, changes like compaction and chemical reactions transform these layers.
During this transformation, the thickness and structure of the original material can change significantly, resulting in what is referred to as a reduction in thickness or volume of the organic layer. This reduction is quantified using percentage decrease to describe how much the material has compacted.

Coal Formation

Coal formation is an intricate process where organic material, primarily from plant debris, transforms into coal over millions of years.
The primary steps include the accumulation and burial of plant material, followed by compaction and chemical transformation under conditions of increased temperature and pressure.
During coal formation, the thickness of the organic layer decreases drastically. Initial thick layers can compact into much thinner coal seams. For instance, a 4-meter layer of organic material could transform into a 1-meter coal seam, showcasing a percentage thickness decrease.
This process involves multiple stages of transformation, including the formation of peat, lignite, bituminous coal, and finally anthracite. Each of these stages reflects the increasing degrees of compaction and carbon concentration, integral to forming different types of coal.