Final answer:
Water is essential to life on Earth because it is a universal solvent, enabling biochemical processes. Its ability to form hydrogen bonds and stabilize temperature supports life-sustaining conditions.
Step-by-step explanation:
Water is essential to life on Earth primarily because it acts as a universal solvent. This characteristic enables water to dissolve a wide range of substances, which is crucial for the biochemical processes that sustain life.
The polar nature of water molecules allows them to form hydrogen bonds, facilitating the dissolution of other polar compounds and ions. It is not because water is a source of energy, composed merely of hydrogen and oxygen, or because it is a greenhouse gas that it is vital for life. While true that water is composed of hydrogen and oxygen and does contribute to the greenhouse effect, its role as a solvent is fundamental for biomolecular reactions.
Additionally, water has the unusual capacity to stabilize temperature due to the continuous making and breaking of hydrogen bonds as temperature changes. This temperature-stabilizing effect is important for maintaining the conditions necessary for life processes. Without the presence of liquid water, which is distinct from its solid (ice) or gaseous (steam) states, life as we know it would not be possible. Earth's ability to support liquid water on its surface is a primary reason it can harbor life.