Final answer:
All of life on Earth is part of the global biosphere, which spans various habitats and includes the Bacteria, Archaea, and Eukarya domains. This region impacts the Earth's atmosphere and reflects light in a unique way, suggesting the presence of life on our planet. The search for life elsewhere stems from the Copernican principle, indicating that life could exist on other planets.
Step-by-step explanation:
All of life on Earth exists in a region known as the global biosphere. This includes all areas that support life, encompassing environments from the depths of the oceans to the expanse of the atmosphere. The biosphere includes diverse habitats where life-forms have evolved to thrive. Scientists have categorized all life on Earth into three domains: Bacteria, Archaea, and Eukarya. Each domain represents a distinct lineage of life that evolved from a common ancestral cell. Earth's robust biosphere reflects planet-scale changes due to life, impacting the composition of the atmosphere and the spectrum of light reflected from the planet. This is observable through telescopic data and demonstrates the distinctive nature of Earth compared to other celestial bodies in our solar system.
Despite current understanding, the principle of Copernicanism suggests that life is likely not unique to Earth, considering the vast number of stars and galaxies in the universe. This forms the basis of the search for extraterrestrial life and the field of astrobiology, which studies the coevolution of life with the environment, both on Earth and potentially elsewhere in the universe.