Part 6/11:
Metallicity, the proportion of elements heavier than hydrogen and helium, is crucial for understanding planet formation. Our sun's metallicity allows for the formation of rocky planets, which is a prerequisite for life as we know it. However, metallicity varies across the universe, with younger stars generally having a higher metallicity due to the accumulation of materials from previous generations of stars.
The rarity of Earth-like planets in terms of metallicity, therefore, can serve as a significant filter, making the emergence of advanced civilizations less likely elsewhere.