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Earth is the third planet from the sun, which is about 93 million miles away. From space, Earth looks like the blue water world it is. About 70% of Earth\'s surface is covered with water, and 97% of all that water is in the salty oceans. Only 3% of Earth\'s water is freshwater, the water we drink. Earth\'s atmosphere is a mixture of gasses that become thinner as we move away from the planet toward space. Most of the atmosphere is nitrogen (78%), oxygen (21%), argon and other gases (1%).
Some of the oxygen in Earth\'s atmosphere has changed over time to form ozone. Earth\'s high ozone layer filters out the sun\'s harmful ultraviolet rays, protecting the creatures living on the surface. But too much ozone helps trap the sun\'s infrared rays. Infrared radiation is heat radiation. It is the warmth you feel when the sun shines on you. If too much heat is trapped in Earth\'s atmosphere, surface temperatures will rise.
This is called the "greenhouse" effect and it\'s what makes Venus so hot. Earth goes around the sun in 365 and 1/4 days. Every 4 years that 1/4 day adds up to one whole day and we add a day to the end of February, creating a leap year. It takes only 24 hours (1 day) for Earth to spin on its axis one time. Earth is covered with mountains, volcanoes, lakes, rivers, and oceans. Most of the surface material is made of rocks high in silica, iron, and magnesium.
The highest point on Earth\'s surface is Mount Everest on the border of Nepal and China at 29,035 feet (8,850 meters). Earth\'s average surface temperature is 45°F. To escape Earth\'s gravity you have to travel at 25,000 miles per hour. Earth has a diameter of 7,926 miles.
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