Final answer:
Earth's orbit within the habitable zone permits water to exist in all three states, which, coupled with a suitable atmosphere and temperature, enables a diverse biosphere. The unique properties of water, including high boiling and melting points, contribute to Earth's ability to support life.
Step-by-step explanation:
The unique characteristic of Earth's orbit allows water to exist in solid, liquid, and gaseous forms. Positioned ideally within the habitable zone of our solar system, Earth is at a perfect distance from the sun, sustaining temperatures that facilitate the presence of liquid water, which is essential for life. The near-circular nature of Earth's orbit contributes to relatively stable climatic conditions that, along with the hydrosphere, make our planet habitable.
Water on Earth is present in vast oceans, lakes, rivers, and also as water vapor in the atmosphere, playing a critical role in the biosphere. Furthermore, Earth's water has high melting and boiling points compared to similar-sized molecules like methane and ammonia, allowing it to remain liquid across a wide temperature range.
Earth's exceptional circumstances, including the presence of liquid water on its surface, a vital atmosphere, and suitable temperatures, have led to a thriving photosynthetic biosphere. These conditions enable life forms to harness energy directly from sunlight, which is a prerequisite for sustaining a complex ecosystem observable from great distances across the cosmos.