The concept of the "Goldilocks zone" or the habitable zone refers to the region around a star where conditions are considered suitable for the existence of liquid water on a planet's surface. It is often used as a starting point in the search for life because water is a fundamental requirement for life as we know it.
While it is true that life can exist in extreme environments on Earth, such as deep-sea hydrothermal vents or caves, where sunlight is absent, these are still dependent on energy sources. In these cases, life forms rely on alternative energy sources, such as chemical reactions driven by geothermal heat or other organic compounds.
The "Goldilocks zone" is used as a guideline because it is based on our current understanding of life and the conditions that support its existence. Life as we know it on Earth is primarily based on carbon chemistry and requires a source of energy to sustain its processes. Sunlight is one of the most abundant and readily available sources of energy, which is why it is often considered a crucial factor in the search for potentially habitable environments.
However, it's important to note that the concept of life as we know it is based on our own planet's biology. There is still much we don't know about the possibilities of alternative forms of life that could exist under different conditions. The search for life beyond Earth is an active and evolving field of research, and scientists are open to the idea that life might exist in environments or under conditions that are different from what we currently understand.
As our knowledge and understanding of the universe expand, our criteria and search strategies for habitable environments may also evolve. Exploration of extreme environments on Earth, such as those devoid of sunlight, can provide valuable insights into the potential for life in other environments beyond the traditional "Goldilocks zone."