Water

There is a lot of water on the Earth. In fact, 71% of the surface of the Earth is covered by water. The Sun has a lot to do with what our water is like and how pure it is and how salty it is.

Ninety-nine percent of the water on Earth is salty. The Sun evaporates the water in the oceans and sends it back to Earth in the form of rain. Each year the Sun evaporates about 95,000 cubic miles of water. Most of the rain that falls back into the oceans and becomes salty again. The rest of the water falls onto the land and goes into the earth or lakes, river, and streams. Some of this flows back into the oceans.

After the Sun has purified the water we have 15,000 cubic miles of it left as "ground water." This clean water gives us enough water for each person on Earth to receive 22,000 gallons of fresh water a year.

What makes rain?

When the Sun warms the water in the ocean, water evaporates into the air. The water vapor goes up it is less dense than air. As it rises, it cools and condenses to form small drops of water again. These droplets are called clouds.

The droplets float around and collect bits of dust and become heavier and heavier until they are too heavy to stay up in the sky and fall back to the ground as rain.

These droplets don't always fall as rain, they can also freeze in the air and fall as hail, sleet, and snow. In fact, a droplet may melt and refreeze several times before it finally hits the ground.

Plants absorb only a little bit of the rain. Some soaks into the ground and some evaporates back up into the sky. Moving water can be very strong. Heavy rains may change way rivers flow. Floods do a lot of damage.

Why do we have tides?

All over the world two times each day the height of the water rises and falls. The rise is called high tide and the fall is called low tide. Tides are caused by the gravity, or pull, of the moon and the Sun. Gravity makes two bulges in the oceans on opposites of the Earth. The bulges are always there they move as the Earth spins on its axis. Sometimes the tides are higher or lower than at other times. This is because of how close or how far away the moon and Sun are from the Earth.