User:Junalyn C. Pascua

THE CHANGING EARTH

The Earth's interior is an interesting subject to study. It is now an accepted fact that forces deep within Earth have helped shape its present surface. Aside from such forces, the earth is also affected by certain forces above its surface. We shall examine these factors and their effects on the lives of people, animals and plants.

LESSON 1: The Earth's Surface The Earth is a planet is almost spherical in shape and is made up of land, water, and air. Large masses of land, called CONTINENTS, comprise about one-fourth of its surface. The remaining part, of about three-fourths, is covered by water. The blanket of air surrounding Earth is called ATMOSPHERE. It contains several gases such as nitrogen, oxygen, argon, carbon dioxide, and other gases in smaller amounts. The layers of the earth are the crust, mantle and the core. CRUST is the outermost layer of the earth. MANTLE which lies beneath the crust, is composed of solid and hot molten rock. And the core is made up of molten iron and nickel in its outer portion and solid materials in the inner structure.

LESSON 2: The Moving Crust Of The Earth Earth's crust is made up of continents and oceans. Its continental and oceanic parts are composed of several large and small moving rock layers called CRUSTAL PLATES. These plates move due to great forces acting on them. This movement is shown by rocks breaking apart. The seven crustal plates on Earth are the Euracian, African, Pacific, Indian, Australian, Antarctic, and American(North and South) plates. About 200 million years ago, there were no crustal plates to speak of. There was only one super continent, Pangaea. This was an idea broke into pieces (crustal plates) and slowly moved until they reached their present position. These crustal plates are said to float over a liquid rock called ASTHENOSPHERE. The crustal plates move. Their movement may be described as moving forward or away from one another. At the edges of the plate, there may be sinking or uplifting at the point where crustal plates collide. When a continental plate collides with an oceanic plate, a trench may be formed. A trench is a very deep place on the ocean floor. When a collision occurs, energy is released. This is felt on the Earth's surface as surface as earthquake tremors. The intensity of the tremor varies. Tremors may be weak or strong.

LESSON 3: Earthquakes When the pencil was pulled upwarrd, the books moved. They seem to tremble. When the books were pressed downward, they also moved. In similar manner, intense heat from the Eath's interior affects the plates. Pressure from above and beneath the crust causes plates to move. The pressure also produces cracks or faults. When energy is released from the moving crustal plates, the surrounding rock layer trembles and shifts. This movementis called EARTHQUAKE. The shifting or movement of the crustal plates gives rise to TECTONIC EARTHQUAKE. When magma moves along a fissure they cause the Earth's crust to tremble, too. The magma may reach the surface and when this happens, a volcanic eruption occurs. Earthquakes caused by volcanic activity are called VOLCANIC EARTHQUAKES. When an earthquake occurs, some places experiences stronger tremors than others. Areas where stronger vibrations are felt are usually near the epicenter of the earhtquake. An EPICENTER is the point on the surface of the Earth located directly above the center of an earthquake's origin. The center or source of the earthquake is called FOCUS. When the crust shakes, such tremor causes damages to people, buildings, bridges, roads, and vegetation. The extent of damage caused by an earthquake is called INTENSITY. Intensity is usually measured in the Rossi-Forel Scale. This scale ranges from intensity I to IX, from the least to the most destructive effect of the earthquake. This scale is based on the effect of the tremor on people and objects. MAGNITUDE, on the ather hand, is the amount of energy released by an earthquake. An american scientist named Charles F. Richter developed a scale to indicate the magnitude of an earthquake. This scale is popularly known as the Richter Magnitde Scale that uses numbers from 1 to 10. The stronger the earthquake is, the higher the number is on the scale. The more feeble or weaker earthquake produces a lower magnitude. Scientists have invented a device that measures the movement of the Earth's crust. It is called SEISMOGRAPH.

LESSON 4: Earthquakes, Environment, and Precautionary Measures When the Earth's crust shakes violently, changes in land features occur. A very strong earthquake can cause some parts of the land to open up, creating wide chasms. It may also give rise to some parts of the soil to erode or crack. The failing of loose rocks along the mountainside is called a LANDSLIDE. An earthquake may happen anytime. An earthquake may happen under the sea. This can cause giant waves in the ocean called TSUNAMI. A tsunami can rise up to 15 meters and can sweep away a whole village near a coastal area. It can kill thousands of people, too. The destruction of properties may run to millions of pesos, as buildings collapse and pipelines break. There is no accurate way to predict earthquakes. Scientists make observations that should serve as clues to impending occurence of an earthquake. Some indicators are occurence of low-magnitude in tremors called FORESHOCKS, changes in water level in wells, as well as changes in animal behaviors. It is important to observe safety precautions before, during, and after earthquakes. When all these precautions are observe properly, damages brought about by earthquakes can be significantly reduced.

SOURCES: INTO THE FUTURE: SCIENCE and HEALTH (Book)

AUTHORS: Juanita M. Cruz

Danilo S. Gutierrez

Victoria S. Ziganay

Helen E. Caintic