If we assume that all Earth-like planets have evolutionary timelines similar to Earth’s, which percentage of Earth-like planets in a 2-billion-year-old star cluster can be estimated to host intelligent life?

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BlackTom AI · Accepted Answer

To tackle the question, I’ll lay out the logic and then evaluate each option.
First, the scenario specifies that all Earth-like planets have evolutionary timelines similar to Earth’s, and we’re looking at a 2-billion-year-old star cluster. On Earth, the emergence of life and especially intelligent life took many billions of years after planet formation, with complex, tool-using intelligence arising well after life first appears. If every Earth-like planet followed a comparable timeline, a 2-billion-year window would be far too short for intelligent life to develop, implying a near-zero likelihood of hosts of intelligent life in that cluster.
Option 30 percent: This would imply a substantial fraction host intelligent life despite the time constraint. Given Earth-like timelines, 2 Gyr is generally insufficient for intelligent life to evolve, so this overestimates the probability and is not consistent with the assumption of Earth-like timelines.
Option 100 percent: This is an extreme absolute claim that all such planets would harbor intelligent life. The time constraint makes this implausible; not every planet would have progressed to intelligence within only 2 Gyr, even under Earth-like evolution, making this option incorrect.
Option 10 percent: A nonzero but small fraction suggests some planets managed to develop intelligence quickly or atypically. While conceivable in some speculative models, the question’s framing emphasizes Earth-like timelines, which argue against a significant fraction developing intelligence within 2 Gyr, so this understated probability is not aligned with the premise.
Option 0 percent: This option states that none of the Earth-like planets could host intelligent life within a 2-billion-year window if their evolution mirrors Earth’s timeline. Given the requirement to parallel Earth-like evolution and the relatively short available time, 0 percent is the most consistent consequence of the stated assumption, making it the correct choice under these conditions.
Option 50 percent: Half of the planets hosting intelligent life would be inconsistent with a strict Earth-like timeline within a 2 Gyr period, making this option clearly incompatible with the premise and thus incorrect.

EESC1120.01|.02 Summer 2025 Our Home Amongst the Cosmos [Kruckenberg] Week 6 Quiz

If we assume that all Earth-like planets have evolutionary timelines similar to Earth’s, which percentage of Earth-like planets in a 2-billion-year-old star cluster can be estimated to host intelligent life?

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