Benjamin Manning, age 15, of Visalia, Calif., for his question:
HOW WAS THE EARTH FORMED?
This place we call home is a giant ball that measures about 8,000 miles through and about 25,000 miles around. It is moving around a bright star we call our sun, and moving with it are other planets. About three quarters of its surface is covered with water. The highest mountain is about five and a half miles, and the deepest spot in the ocean is about seven miles.
No one knows exactly when the earth was formed or how. There are many scientific theories, including the most accepted one that says our earth probably started as a glowing mass of gases which slowly cooled to liquids and then solids. While the gases were bubbling, the heavy metals were most likely settling toward the center of the ball.
Earth's formation probably came about as the gas burned and escaped to form an atmosphere while the molten rocks cooled and formed a crust. The crust was most likely broken and rebroken many times as rocks cooled, but slowly it became more stable and more thick.
As the atmosphere cooled, water vapor from the gases condensed and fell as rain on the cooling rocks. In time, water was collected in low places and oceans were formed. In the earth's early days, it was most likely covered with bare rocks. Volcanoes probably spouted great lava flows and the seas were most likely hot.
As the earth continued to cool, the crust grew thicker. We now believe the crust is about 40 miles thick, below which is a layer of denser, solid rock about 1,700 miles deep. This layer is called the mantle. And below that is a zone about 1,400 miles deep (called the outer core) of hot, molten rock under tremendous pressure. Scientists believe that at the earth's inner core is a solid ball about 1,600 miles across composed or iron and nickel and other metals. The inner ball and the molten zone together make up the core of earth.
The cooling earth caused warping and buckling of the crust. Then some of the lighter weight rocks that had been sunken were pushed upward. The Appalachians and the Rockies were probably formed this way, rising from ancient sea bottoms.
Earthquakes that happen in various parts of the world these days tell us much about what the inside of earth is like. We can chart the kinds of earthquake waves and the time it takes for them to go from one point to another.