Natural Causes of Biodiversity Loss
Biodiversity loss is a natural process of evolution of biological communities. With time some species become extinct and some new species are evolved. Among the natural factors of biodiversity loss important causes are climatic changes at global level, prolonged drought and famine conditions, collision of the earth with the celestial bodies such as asteroids and meteoroids, volcanic eruption mainly fissure lava flow, continental drift and fragmentation etc. The onset of ice age and continental glaciation results in covering of ground surface with thick ice sheets, which results in mass extinction of species of biological communities.
Two great ice ages, such as Carboniferous and Pleistocene ice age, have been responsible for loss of several species of plants and animals. The collision of the celestial bodies with the earth results in the generation of immense volume of dust which form thick veils in the lower atmosphere. These dust veils obstruct the solar radiation waves in reaching the earth's surface and hence temperature is remarkably reduced to very low amount of insolation reaching the earth. Such a situation causes cold climate and thus the organisms of warm climates cannot adapt to sudden change in climatic conditions and hence die. Such a situation happened during the Cretaceous period when a giant meteorite collided with the earth and the resultant dusts caused the mass extinction of dinosaurs. Besides, 50 percent of other species also disappeared.
The Permo-Carboniferous glaciation of the Gondwanaland about 250 million years ago resulted in the loss of 54 percent of families, and 90 percent of species became extinct due to an extreme cold condition. The rapid lava flow during fissure eruption of volcanoes covers larger areas and the existing species of plants and animals are buried under thick covers of hot lava and thus become extinct. Such a situation occurred during Cretaceous period when there was a widespread volcanic activity the world over.
The collision of the celestial bodies with the earth results in
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → obstruction of solar radiation
The collision produces thick veils of dust, and "These dust veils obstruct the solar radiation waves in reaching the earth's surface". Less sunlight reaches the ground, so the temperature falls sharply.
Why the Other Options are Incorrect?
Option 1: obstruction of ozone layer — Incorrect. Not mentioned: the passage says nothing about the ozone layer.
Option 2: obstruction of ultra-violet rays — Incorrect. Too narrow: the passage speaks of solar radiation as a whole, the sun's heat and light, and links it to the fall in temperature; ultra-violet rays are not named.
Option 4: obstruction of infra red rays — Incorrect. Too narrow: infra-red rays are not named either; the passage says solar radiation.