Rita M. O’Keefe
The first section focuses on types of rocks. The three types of rocks include igneous, sedimentary and metamorphic. The first type to form were the igneous, or primary, rocks. Igneous rocks are formed at high temperatures. They are still forming today and can be seen as the hot lava or magma that flows from a volcano. Igneous rocks are the rocks that form when the lava cools and becomes solid. The rocks can be recognized by their crystals. Glassy obsidian has few tiny crystals, basalt contains very fine crystals, and gabbro has large crystals. A second type of rock is called sedimentary rock. When rocks are worn away by the weather, they break down into smaller pieces of rocks and minerals, forming sediment. Sediments harden into sedimentary rocks or rocks made of pieces of other rocks. They contain grains of material which are held together by different kinds of natural cement. The grains frequently show bands or patterns running through them. Some sedimentary rocks may be made of shells of sea creatures or possibly of salt layers. Common sedimentary rocks include sandstone, limestone, chalk, clay, conglomerate and breccia. A third type of rock is metamorphic. All metamorphic rocks have been changed from other kinds of rock. The changes are usually caused by great heat within the earth, pressure from movements in the earth’s crust, or by a combination of both. Magma, the hot liquid rock inside the earth’s crust moves into cracks in sedimentary rocks and may also flow between its layers. The heat of the magma causes a chemical reaction. Chemical elements in the magma react with chemical elements in the rocks. Thus new minerals and metamorphic rocks are formed.
From a physical science standpoint the concepts of force, pressure, phase change and temperature are significant. Force can be thought of as a push or a pull. A force will always act in a certain direction. Friction makes it hard to move objects. Force is needed to overcome the force of friction. The amount of force acting on a surface is called pressure. Pressure can be changed by changing the force. If the area stays the same, increasing the amount of force increases the pressure. Pressure acts in gases and liquids, as well as in solids. This pressure in gases and liquids is referred to as fluid pressure. Phases of matter must also be considered when studying earth science. Different forms of the same substance are called phases. The three phases of matter include solids, liquids and gases. A solid is a phase of matter that has a definite shape and volume. In a solid, particles of matter are packed together tightly and as a result are not able to change position easily. They can only vibrate. A liquid has a definite volume, but no definite shape. Liquids can change shape because the particles in the liquid are able to slide past each other and change their position. A gas is a phase of matter that has no definite volume or shape. The particles in gases are constantly moving. When matter changes from one phase to another it is called a phase change. During a phase change, there is also a change in heat energy, so temperature is directly related to changes in the states of matter.
