Question

Which is a sedimentary rock formed from decayed plant matter? A. biomass C. natural gas B. coal D. oil Use the graph below to answer questions 2 and \(3 .\) Energy Use in the United States, 2002

Short answer

The sedimentary rock is coal.

Step-by-step solution

Understand the Question

The question asks us which material, formed from decayed plant matter, qualifies as a sedimentary rock. The options provided include 'biomass', 'natural gas', 'coal', and 'oil'.

Define Sedimentary Rocks

Sedimentary rocks are typically formed by the accumulation and compaction of mineral and organic particles on the Earth's surface, especially in bodies of water. They can include organic materials like plants.

Identify the Formation Process

Decayed plant matter that forms a sedimentary rock typically goes through a series of stages including compression and heating over time, resulting in a material rich in carbon.

Evaluate Each Option

- **Biomass**: Renewable biological material derived from plants and animals, not a sedimentary rock. - **Natural Gas**: A fossil fuel, primarily methane, not a rock. - **Coal**: A sedimentary rock formed from the accumulation of plant debris, subjected to heat and pressure. - **Oil**: A liquid fossil fuel, not a sedimentary rock.

Choose the Correct Answer

Based on the evaluation, 'coal' is the sedimentary rock that forms from decayed plant material over millions of years through compaction and heating.

Key concepts

Coal Formation

Coal is a type of sedimentary rock that plays a fundamental role in our energy landscape. It forms over millions of years from decayed plant matter, such as trees, ferns, and other vegetation that thrived in prehistoric wetlands. These plants die and accumulate in swampy environments, where they are covered by layers of sediment.
Over time, the weight of the overlying materials compresses the plant debris, initiating a process called compaction. As layers of sediments build up, the temperature also rises due to geological heat, which transforms the organic material through chemical reactions.
This entire process, known as coalification, creates carbon-rich compounds, ultimately forming coal. The type of coal that forms depends on the degree of heating and pressure. There are four main types of coal: lignite, sub-bituminous, bituminous, and anthracite, ranging from least to most carbon-rich. Each stage signifies coal's quality and energy-producing potential.

Decayed Plant Matter

Decayed plant matter is a critical component in the formation of coal and other natural resources. The initial stages occur when plants die and become buried under water in swampy environments. The aquatic ecosystem helps prevent complete decomposition, allowing the plant matter to accumulate over time.
As layers of sediment build on top, they exert pressure on the buried plant matter, reducing the amount of oxygen. This anaerobic (without oxygen) environment is key to preserving the plant material and gradually turning it into peat, the precursor to coal.
The plant matter undergoes various chemical changes, losing elements such as hydrogen and oxygen while becoming more enriched in carbon. This transmutation is crucial because higher carbon content in coal corresponds to higher stored energy, making coal an efficient fossil fuel. The understanding of this transformation highlights the interplay between geology and biology in Earth’s historical energy preparation.

Fossil Fuels

Fossil fuels, including coal, oil, and natural gas, are the remains of ancient organic materials that have decomposed and transformed over millions of years. Coal stands out as a sedimentary rock, whereas oil and natural gas are generally found in liquid or gaseous states.
The term "fossil fuels" arises from their origination in prehistoric life forms that absorbed energy from the sun through photosynthesis. After these organisms died, they settled in thick layers on the seabed or ground. Geological processes then buried these remains deeper over time.
In the depths of the Earth, intense pressure and heat converted the organic matter into hydrocarbons, the primary molecular constituents of fossil fuels. These fuels can be extracted and burned to release the energy stored millions of years ago, highlighting their role as significant energy sources in modern society. However, their extraction and use have substantial environmental implications, driving today's energy discussions and sustainable efforts.