Final answer:
Sunlight and gravity are the main factors responsible for Earth's water cycle.
Step-by-step explanation:
The two factors mainly responsible for Earth's water cycle are sunlight and gravity. Sunlight provides the energy needed to evaporate water from oceans, lakes, and other sources, while gravity plays a role in the movement of water from one part of the cycle to another. When water vapor condenses to form clouds, gravity causes the water droplets to fall back to the Earth as precipitation.
Learn more about Earth's water cycle