How does the Faint Young Sun paradox challenge our understanding of early Earth's climate?
Show answer & explanation
Correct answer: C
Explanation
Answer: It suggests that early solar output was too weak to prevent global freezing.
Explanation: The Paradox: With such a "faint" Sun, the early Earth should have received significantly less heat. Theoretically, the temperature would have been well below the freezing point of water, turning Earth into a global "snowball."
The Challenge: However, geological evidence (such as sedimentary rocks) shows that liquid water and life existed on Earth very early on.
The Conflict: The paradox challenges us to explain how Earth stayed warm enough for liquid water when the Sun was so weak. Scientists believe high concentrations of greenhouse gases (like Carbon Dioxide and Methane) or a lower planetary albedo (reflectivity) acted as a blanket to keep the planet warm.
Key Facts for Exams
Sun's Age: The paradox concerns the period between 2.5 to 4 billion years ago.
Solar Luminosity: The Sun’s output increases over time; in the early stages, it was only about 70% of its current strength.
Main Greenhouse Gases: The most likely "solutions" to the paradox involve CO₂ and Methane (CH_4), which were much more abundant in the early atmosphere than they are now.
Exam-Related Practice Questions
Q1: By approximately what percentage was the Sun's luminosity lower during the early stages of the solar system compared to today?
Answer: Approximately 25–30%.
Q4: Who were the scientists who first proposed the Faint Young Sun paradox in 1972?
Answer: Carl Sagan and George Mullen.