A research team examined a long-term owl roost. Owls prey on small mammals and the excreted remains of those meals that accumulated over the time, provide us an insight into the composition and structure of small mammals over the past millennia. The research suggested that when file Earth went through a period of, rapid warming about 13,000 years ago, the small mammal community was stable and resilient. But, from the last quarter of the nineteenth century, human-made changes to the environment had caused an enormous drop in biomass and energy flow. This dramatic decline in energy flow means modern ecosystems are not adapting as easily as they did in the past:

Question: On the basis of the above passage, the following assumptions have been made:
1. Global warming is a frequently occurring natural phenomenon.
2. The impending global warming will not adversely affect small mammals.
3. Humans are responsible for the loss of the Earth’s natural resilience.
Which of the above assumptions is/are valid?

The correct option is 3 only.

Step-by-step Explanation:

To determine the validity of the assumptions based on the provided passage, we can analyze each one individually:

1. Analysis of Assumption 1: "Global warming is a frequently occurring natural phenomenon."
The passage mentions a specific period of rapid warming that occurred about 13,000 years ago. However, it does not state or imply that global warming is a "frequently occurring" phenomenon. We cannot assume frequency or regular occurrence based on a single historical event mentioned in the text. Therefore, Assumption 1 is invalid.

2. Analysis of Assumption 2: "The impending global warming will not adversely affect small mammals."
The text points out that during the rapid warming period 13,000 years ago, the small mammal community was stable and resilient. However, it also highlights that human-made environmental changes since the late 19th century have caused a massive drop in biomass and energy flow, meaning modern ecosystems are not adapting as easily as in the past. Because modern ecosystems (including small mammals) have lost their resilience, we cannot assume that future/impending global warming will not adversely affect them. Therefore, Assumption 2 is invalid.

3. Analysis of Assumption 3: "Humans are responsible for the loss of the Earth’s natural resilience."
The passage explicitly contrasts the past resilience of the ecosystem (during the warming 13,000 years ago) with the modern state. It states that "human-made changes to the environment had caused an enormous drop in biomass and energy flow," leading to the conclusion that "modern ecosystems are not adapting as easily as they did in the past." This directly links human actions to the degradation of the ecosystem's adaptive capacity (resilience). Therefore, Assumption 3 is a valid assumption supported by the passage.

Thus, only Assumption 3 is valid, making 3 only the correct answer.