M an has studied Earth ever since we came to exist. We have looked around us and questioned any and everything that we found. Humans expansive knowledge of our home planet is one reason that we have risen to be the most dominate species on Earth. We have tested and retested many of the theories about our Earth in order to better understand it and our place in the universe.

S cientist believe that the Earth is at least about 4 1/2 billion years old. They came to this conclusion since the oldest rock ever found is about 3 1/2 billion years old and since the Earth recycles its rocks through heating them in the Earth's core and ejecting lava out through volcanoes it must be at least one billion years older than that rock. Many of the discoveries about our planet are due to rocks that scientist find in various places around the world. These rocks are known as the fossil record and serve as a geological time line that tells scientists where and when different planetary events occurred.

W e never realized how much we really didn't know about our planet until we started to send satellites out into space to orbit and help us study it. The first of these satellites was known as Explorer I and was was sent up by the United States in 1967. Explorer I discovered a very intense radiation zone that is doughnut-shaped and surrounds the equator which is called the Van Allen radiation belts. This region is caused by rapidly moving charged particles that become trapped by the Earth's magnetic field by the equator.

W e also found out that our planet's magnetic field is distorted into a tear-drop shape by solar wind. Solar activity causes a very dramatic visual effects at certain times of the year. When charges particles from the solar wind become trapped in our magnetic field they collide with air molecules that orbit above the Earth's magnetic poles and begin to glow. This glowing is known as the auroras or the northern lights.

S ubsequent trips to outer space by astronauts and explorer satellites keep turning up new and interesting discoveries about our planet. It seems the more we learn, the more we see how much is undiscovered.