What is the defining property of Earth that supports life?

The defining property of Earth that supports life is the presence of water. Water is essential for all known forms of life; it acts as a solvent, allowing biochemical reactions to occur within organisms. It is crucial for processes such as photosynthesis in plants, which produces oxygen and organic materials that support numerous life forms.

Water also moderates temperature, affecting climate and weather patterns that further sustain diverse ecosystems. The unique ability of water to exist in all three states (solid, liquid, gas) under Earth's environmental conditions allows for complex interactions within ecosystems.

While the other choices, such as a strong magnetic field, stable climate, and rich soil, contribute to making Earth a hospitable environment, they are secondary to the fundamental role water plays in sustaining life itself. Without water, life as we know it would not survive; therefore, its presence is central to Earth's capacity to support life.