UGC NTA NET/JRF Exam, Environmental Sciences, March-2023

Natural extinction is the process by which species that cannot adapt to changes in their environment ultimately disappear.

Over the vast timescales of Earth's history, countless species have emerged, evolved, and eventually gone extinct due to various reasons, such as environmental changes, competition with other species, or catastrophic events.

While mass extinctions (like the one that wiped out the dinosaurs) and anthropogenic extinctions (caused directly or indirectly by human activities) are specific types of extinctions, the term "natural extinction" encompasses the inherent ebb and flow of species over geological time.

It's crucial to differentiate natural extinctions from those accelerated by human activities, as the latter often occurs at a rate much faster than the environment's capacity to adapt.

Incompatible elements are those elements that do not fit well into the crystal lattices of the primary minerals that crystallize from a magma during its cooling and solidification.

Due to this incompatibility, these elements tend to remain in the liquid phase until the very last stages of crystallization, often concentrating in the residual melt.

These elements are valuable in the study of igneous processes because their concentrations can provide clues about the history of a given magma and the processes it has undergone, such as fractional crystallization or magma mixing.

The ocean floor is primarily destroyed at convergent plate boundaries. Here, tectonic plates move towards each other, and one of the colliding plates is forced beneath the other in a process called subduction.

When oceanic crust is subducted beneath another oceanic or continental plate, it sinks into the mantle where it melts and is recycled. This process is responsible for the formation of deep-sea trenches, the deepest parts of the world's oceans.

The Mariana Trench in the western Pacific, for example, is formed by the subduction of the Pacific Plate beneath the Mariana Plate.

When estimating geothermal resources, the focus is primarily on understanding the heat contained within the Earth and how it can be harnessed for energy.

Key considerations include the depth, thickness, and extent of the geothermal aquifer; properties of the rock formation surrounding the aquifer (as this affects heat conductivity and storage); and the salinity and geochemistry of the fluid within the aquifer (since this impacts the efficiency of energy extraction).

Fossil content of rocks, while fascinating for paleontological studies and understanding Earth's history, is not directly relevant to the estimation of geothermal energy potential.

Shale gas is predominantly composed of methane (CH₄). Methane is the simplest hydrocarbon with a single carbon atom and four hydrogen atoms. Shale gas is found trapped within shale formations, which are fine-grained sedimentary rocks.

The gas is formed over millions of years as organic material within the shale breaks down under heat and pressure.

The widespread adoption of hydraulic fracturing (or "fracking") technology has allowed for the extraction of shale gas from formations that were previously uneconomical to tap, leading to a boom in shale gas production in countries like the United States.

While shale gas provides a significant energy resource, concerns about environmental impacts, including groundwater contamination and induced seismicity, have accompanied its extraction.

Gas hydrates are crystalline solids formed from water and gas, where gas molecules, typically methane, are trapped in cages of hydrogen-bonded water molecules.

They typically form under high pressures and low temperatures. There are several methods proposed for producing methane from gas hydrates, including:

• Thermal stimulation: Heating the hydrate to release the trapped gas.

• Depressurization: Reducing the pressure to dissociate the hydrate.

• Chemical inhibition: Introducing chemicals that break down the hydrate structure. However, "Bacterial recovery" is not a known method for producing gas from hydrates.

It's worth noting that extracting methane from gas hydrates poses challenges and concerns, including potential geohazards and impacts on climate due to methane's potency as a greenhouse gas.

Proximate analysis of coal provides information about its moisture content, volatile matter, ash, and fixed carbon content.

It does not directly measure the sulfur content of coal. Sulfur content is essential to know because when coal burns, sulfur dioxide (SO2) is released, a significant air pollutant and a precursor to acid rain.

The sulfur content of coal can vary depending on its source and type. There are specific analytical technique separate from proximate analysis that are used to determine sulfur content, and these fall under the "ultimate analysis" category.

Bioenergy refers to energy obtained from biological sources. It can be derived from plant and animal matter, making it a renewable source of energy, as these resources can be replanted or replenished over time.

Common forms of bioenergy include biofuels like ethanol and biodiesel, biogas from anaerobic digestion, and wood or crop residues burned for heat or electricity.

Because bioenergy relies on materials that grow (like plants), it can be continually renewed, unlike fossil fuels, which deplete over time.

However, the sustainability of certain bioenergy practices is a topic of debate, with concerns over land use, impacts on food supply, and overall carbon neutrality.

When a plume from a smokestack is released under a temperature inversion layer, the behavior is called "Fumigation." Temperature inversions occur when warm air overlays cooler air near the ground, preventing the vertical mixing of air.

When a plume is released into such conditions, it can become trapped beneath the inversion layer, causing it to spread out horizontally.

This can lead to high concentrations of pollutants at ground level, impacting air quality and posing health risks.

Such scenarios underscore the importance of understanding atmospheric conditions and their implications for pollution dispersion and control.