NCERT Solutions for Class 8 Science Chapter 5
Important NCERT Questions
8th Chapter 5 Coal and Petroleum
NCERT Books for Session 2022-2023
CBSE Board and State Bord
Questions No: 3
Describe how coal is formed from dead vegetation. What is this process called?
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About 300 million years ago the earth had dense forests in low lying wetland areas. Due to natural processes, like flooding, these forests got buried under the soil. As more soil deposited over them, they were compressed. The temperature also rose as they sank deeper and deeper. Under high pressure and high temperature, dead plants got slowly converted to coal.
As coal contains mainly carbon, the slow process of conversion of dead vegetation into coal is called carbonisation.
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Coal forms from deceased vegetation through a gradual process known as “coalification.” Here’s an overview:
1. Peat Formation: Dead plant matter, like trees and ferns, accumulates in waterlogged areas like swamps. Under anaerobic conditions, the plants partially decompose, forming a layer of peat over time.
2. Burial and Compression: Sediment layers gradually cover the peat, subjecting it to increasing pressure from the layers above. This pressure compresses the peat, expelling water and gases, transforming it into lignite, a soft brown coal.
3. Heat and Pressure Transformation: Deeper burial and geological forces exert more heat and pressure on the lignite. This process expels more moisture and volatile matter, causing further compression and chemical changes. This results in sub-bituminous coal, bituminous coal, and eventually anthracite, a harder, glossy coal with higher carbon content.
The process of coalification spans millions of years, gradually transforming organic matter into coal due to geological forces. This progression leads to various types of coal distinguished by their carbon content and characteristics.