human
Why is the Earth's surface covered with water?
assistant
The Earth’s surface is covered with water because of the greenhouse effect. When sunlight hits the Earth’s atmosphere, it causes some of the light to be reflected back into space. This reflection is what makes the sky blue and the sun look yellow. However, a small portion of this light is absorbed by the Earth’s surface, which then heats up. This heat causes more water vapor to be released into the air, which further traps more heat from the Sun, causing the planet to warm even more. This process continues until the temperature reaches the boiling point of water, at which point all of the water vapor in the atmosphere will turn into liquid water.