
Passage: The Sun about 2 billion years ago was 30% dimmer than it is today. If the sun was as dim now as it was then, Earth's oceans would freeze completely into ice. However, there is fossil evidence that; liquid water and life existed on Earth as early as 3.8 billion years ago.
Question: If the following statements are true, which of the following would most help to eliminate the apparent inconsistency in the above description?
A. A.The Earth's atmosphere 3.8 billion years ago could hold significantly more heat than it can hold today
B. B.Liquid water that appeared on Earth 3.8 billion years ago later froze and only re-thawed about 2 billion years ago
C. C.About 2 billion years ago, a powerful non-Sun source of heat melted large chunks of Earth's ice
D. D.Evidence suggests that certain areas of the ocean have been frozen until later than 2 billion years ago
Answer: