Q. With reference to mass extinction of species, consider the following statements:
1. It refers to a period when the Earth loses more than three-quarters of its species in a geologically short period of time.
2. After a mass extinction, the earth cannot regain species comparable to those existed before the event.
Which of the statements given above is/are correct? 
Statement 1 is correct: Mass extinction refers to a substantial increase in the degree of extinction or when the Earth loses more than three-quarters of its species in a geologically short period of time.
Statement 2 is incorrect: So far, during the entire history of the Earth, there have been five mass extinctions occurred due to natural phenomena. After each of these extinctions, it took millions of years to regain species comparable to those that existed before the event. Thus, it is incorrect to say that the species cannot be regained after a mass extinction.
The sixth, which is ongoing, is referred to as the Anthropocene extinction caused by man-made phenomena. Researchers have described the sixth one as the “most serious environmental problem” since the loss of species will be permanent.
Source: Sixth Mass extinction
