Find the incorrect statement .

Options

A. Sixth extinction' is different from previous extinction terms of rate of extinction.
B. Ecologists warn that if the present trend of extinction continues , nearly 50 percent of all species on earth might be wiped out within the next 100 years.
C. Amphibians appear to be more vulnerable to extinction.
D. Recent extinction is completely natural.

Answer

To find the incorrect statement from the options provided, we will analyze each statement one by one.

### Step-by-Step Solution:

1. **Analyze the First Statement:**
- The statement claims that the sixth extinction is different from previous extinctions in terms of the rate of extinction.
- This statement is true. The current extinction rate is estimated to be 100 to 1000 times higher than the natural background extinction rates.

2. **Analyze the Second Statement:**
- This statement warns that if the current trend continues, nearly 50% of all species on Earth could be wiped out within the next 100 years.
- This statement is also true. Current species extinction rates are indeed much faster than in pre-human times, largely due to human activities.

3. **Analyze the Third Statement:**
- The statement mentions that amphibians appear to be more vulnerable to extinction.
- This statement is true. Amphibians are indeed among the most susceptible groups to extinction due to various factors, including habitat loss and climate change.

4. **Analyze the Fourth Statement:**
- This statement claims that the recent extinction is completely natural.
- This statement is false. The current extinction events are primarily driven by human activities, such as habitat destruction, pollution, and climate change.

### Conclusion:
Based on the analysis, the incorrect statement is the fourth one: "the recent extinction is completely natural."

### Final Answer:
The answer is **Option 4**.

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