When you are done, take the Earth Quiz:
The earth was formed in the same way as the sun, planets, stars. At first the earth was a hot glowing ball of white hot gases with a temperature that was millions of degrees Fahrenheit. This was caused by particles of gases being drawn together and compressed, giving off a lot of heat. This happened millions of years ago.
Finally the earth cooled down. The ball of gas slowed down from spinning and the color changed from white to yellow to red to not giving off any light at all.
The earth contracted, getting smaller and the gases changed to liquid as they cooled. Heavier materials drew to the center of the earth. The heavier liquid settled at the middle of the earth. As the earth cooled more, a solid crust formed over the over the liquid material. As the crust cooled, it got wrinkled and burst open in spots. Gradually cracks formed in the crust. Water that formed under the earth's crust escaped from the cracks in the earth and soon water vapor formed above the earth. This lead to cloud formation. Larger droplets formed in the clouds and as they were pulled to the earth by gravity came the first rainfalls. The rain at first evaporated as soon as it hit the earth. Later, as the earth continued to cool, the rain stayed on to form lakes and oceans. At first the water was all fresh water, but as it had chemicals from the earth's crust mix in, the water of the oceans became salty. At one time the earth was all water on its surface.
Later pressure and heat in its center pushed up solid portions of the earth that became land forms. Sometimes the land would sink back down and other portions arise.
About three million years ago, the earth cooled a great deal and great sheets of ice called glaciers covered its surface. As the ice spread over the land, it gouged great valleys, rivers and lakes into the earth. About 8000 years ago the last glaciers melted, with the earth more as it is today.
The part of the earth we live on is a very thin layer relative to the inner earth. Looking at the cutaway earth below, the earth has several layers.
The innermost layer is the core of the earth. It is about 4000 miles thick. It has two parts, the inner core which is red on the diagram below and the outer core which is melon colored. The inner core is very hot is very hot and made of heavy metals, mostly iron.
The next layer which is yellowish in color is the mantle. It is made up of a rock called peridodite which is heavier than the earth's rocks.
The layer that we live on is called the crust and is the thin brown layer on the diagram. It is thickest under the continents and thinner under the oceans. It is about 50 miles down at its thickest. The crust is actually not as solid as it feels to us and shifts, sometimes abruptly during earthquakes, and very slowly as when continents drift. The different pieces of the earth's crust are referred to as plates, and their movements towards and away from each other are called plate tectonics.
The earth's age has been estimated to be between 4 and 5 billion years old.
8th Grade Online Quiz Page