Concept explainers
Introduction:
Biodiversity is defined as the richness of the living systems present at all the levels of
Answer to Problem 1TYK
Correct answer:
The greatest extinction in the history of life on the earth might be occurring now.
Explanation of Solution
Justification for the correct answer:
Option (e) states that ‘the greatest extinction on the earth may be occurring now.’ The biodiversity is now declining rapidly. It is occurring much faster than it might have occurred in the history of the earth. The reasons behind the greatest extinction are threats to the biodiversity. There are three major threats to biodiversity, namely deforestation, over-exploitation of fish population, and alteration of freshwater ecosystems. Hence, option (e) is correct.
Justification for the incorrect answers:
Option (a) states that ‘the greatest extinction on the earth occurred at the end of the Permian period.’ The Permian period ended with a Permian–Triassic extinction event, in which nearly 96% of the marine species and 70% of the terrestrial vertebrates became extinct. The present day extinction is going at a faster pace than the Permian period’s extinction. So, it is an incorrect option.
Option (b) states that ‘the greatest extinction on the earth occurred at the end of the Cretaceous period.’ The Cretaceous period ended with the event of Cretaceous–Paleogene extinction, which led to the non-avian dinosaurs, large marine reptiles, and pterosaurs extinction. It is still not the greatest extinction in the history of the earth. So, it is an incorrect option.
Option (c) states that ‘at the end of the Ordovician period, the greatest extinction occurred on the earth.’ The Ordovician period ended with the Ordovician–Silurian extinction event, which led to the extinction of invertebrates including mollusks and arthropods. This did not end with mass extinction. So, it is an incorrect option.
Option (d) states that ‘the greatest extinction took place at the end of the Cambrian era.’ The Cambrian era ended with the Cambrian–Ordovician extinction event, in which many brachiopods and conodonts got extinct. The greatest extinction did not take place at the end of this era. So, it is an incorrect option.
Hence, options (a), (b), (c), and (d) are incorrect.
Thus, it can be concluded that the greatest extinction might be occurring now and did not take place at the end of the Permian, Cretaceous, Ordovician, and Cambrian era. The current extinction is taking place due to human activities.
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Chapter 55 Solutions
Biology: The Dynamic Science (MindTap Course List)