Previous Year Question
Which of the following statements are correct about the deposits of “methane hydrate”?
Global warming might trigger the release of methane gas from these deposits.
Large deposits of “methane hydrate” are found in Arctic tundra and under the seafloor.
Methane in atmosphere oxidises to carbon dioxide after a decade or two.
Select the correct answer using the code given below:
1 and 2 only
2 and 3 only
1 and 3 only
1, 2 and 3
Correct Answer: D
Detailed Solution
Methane hydrate is an ice-like solid crystalline structure in which methane molecules are trapped inside cages formed by water molecules.
It is also known as methane clathrate, hydromethane or methane ice.
Methane hydrate remains stable under conditions of low temperature and high pressure.
Statement 1 is correct: An increase in the temperature of seawater or the permafrost layer may destabilise methane hydrate.
Its decomposition may release methane gas and affect the stability of sediments and marine geomorphology.
A portion of the released methane may be oxidised by microorganisms in marine sediments and the water column; therefore, all released methane does not necessarily reach the atmosphere.
Nevertheless, methane reaching the atmosphere may produce additional warming, creating the possibility of a positive feedback that destabilises more hydrate.
There is considerable scientific uncertainty regarding the actual quantity, rate and climatic impact of this process.
Statement 2 is correct: Large stores of methane hydrate occur in Arctic permafrost or tundra regions and marine sediments along continental margins.
These deposits form in sedimentary regions where methane produced from organic matter combines with water under low-temperature and high-pressure conditions to form a crystalline structure.
Gas hydrates may also occur in the sediments of certain deep freshwater lakes.
Gas-hydrate prospects have been studied in India’s Krishna-Godavari, Mahanadi and Andaman offshore regions.
Statement 3 is correct: The average atmospheric lifetime of methane is approximately a decade.
It reacts mainly with hydroxyl radicals in the troposphere and is progressively oxidised into carbon dioxide and water.
Therefore, the conversion of atmospheric methane into CO₂ over a timescale of a decade or two is correct.
Methane remains in the atmosphere for a shorter period than CO₂, but its heat-trapping capacity per molecule is much greater.
Methane hydrate represents a potentially vast energy resource, but its extraction carries risks such as sediment instability, damage to marine ecosystems and uncontrolled methane leakage.