Passage Summary: A scientist argues that life was on land much earlier than people think. They point to 1.2-billion-year-old rocks containing carbon 14, which is usually a sign of biological activity from things like bacteria or plants.

Conclusion: The common belief that life did not exist on land until 500 million years ago is incorrect.

Reasoning: Rocks that are 1.2 billion years old contain traces of carbon 14, a substance that is typically processed and released by living organisms like plants and microbes.

Analysis: This is a Strengthen EXCEPT question, so we need to identify which four options bolster the link between the presence of carbon 14 and the existence of ancient land-based life. The argument relies on the assumption that the carbon 14 found in these specific rocks actually originated from biological processes on land at that time. Look for an answer choice that either fails to support this biological origin or perhaps suggests the carbon 14 could have come from a non-living source. The four 'wrong' answers will likely rule out alternative explanations or provide more evidence that the carbon 14 is indeed a biological footprint.