7.6 - Solids. Solids. Crystalline solids are classified into four categories:

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1 Solids A solid at the same temperature as a liquid or a gas will have the same average kinetic energy since temperature is a measurement of the kinetic energy of a substance. This means that solids are in constant motion, but their particles have very strong intermolecular forces of attraction and therefore low internal energy. Therefore the motion of the particles in a solid is vibrations around fixed locations. Many solids are in a crystalline form in that the particles are arranged in an orderly, geometric structure. Crystalline solids are classified into four categories: Covalent Network Solids Atoms such as carbon and silicon form multiple covalent attractions that result in very hard and very strong melting point solids with poor conductivity. Carbon graphite and carbon diamond (called allotropes of carbon same element with different forms) are examples as well as SiO 2 which is called quartz or silica. Metallic Solids Positive metal ions surrounded by a sea of mobile electrons result in higher melting points, malleable and ductile solids that conduct electricity very well. Solid zinc or magnesium would be examples of metallic solids. Ionic Solids Positive (cation) and negative (anion) ions that have transferred electrons and form very strong ionic attractions that result in a brittle solid with a high melting point and poor conductivity. Sodium chloride (NaCl) is an example of an ionic solid.

2 Covalent or Molecular Solids Solids held together by hydrogen bonding attractions and dispersion forces that result in lower melting points and poor conductivity. Even though sugar has weaker attractions, its large molar mass results in many small attractions and therefore a solid at room temperature. Density It is often said that iron is heavier than wood. This is not always the case since one could have a very large amount of wood in comparison to one iron nail. What should be stated is that iron is more dense than wood. Density (symbol ρ or the Greek letter rho) is defined as an object s mass per unit volume or: (density)ρ = m V Density is an intensive property which means that it is independent of the amount of sample that is measured. Therefore, if one has a sample of pure gold, both a large amount and a small amount, the density of any sample will be the same. The units for density are either kg/m 3 or g/ml depending upon what we are measuring. Example: A sample of pure gold is measured to have a mass of 96.5 kg when its volume is m 3. What is the density of pure gold? Answer: ρ = m V 96.5 kg = = kg/m m3 Example: A student obtained a piece of aluminum measuring 0.01 m x 0.03 m x 0.5 m. Aluminum is known to have a density of 2700 kg/m 3. What will be the mass of this piece of aluminum? Answer: Volume = l w h = (0.01 m 0.03 m 0.5 m) = 1.5 x 10 4 m 3 m = ρ V = (2700 kg m 3) (1.5 x 10 4 m 3 ) = kg

3 Earth s Interior The earth is divided into three layers the crust, the mantle, and the core. Each layer is made up of a specific set of compounds both ionic and covalent, and has different temperatures and pressures. The Crust The crust is the outermost layer of the Earth and it is 5 to 100 kg thick. It is the thinnest of the three layers, only makes up less than 1% of the Earth s mass, and it consists of two types of layers of crust continental crust and oceanic crust. Both continental and oceanic crusts are made mainly of the elements oxygen, aluminum, and silicon. However, the oceanic crust is much denser since it has almost twice as much iron, calcium, and magnesium. The oceanic crust consists of a dark, fine textured rock named basalt, whereas the continental crust consists of rocks such as granite. The Mantle The mantle is the middle layer of the Earth and is much thicker (nearly 3000 km thick) and warmer than the crust as well as contains most of the Earth s mass. The mantle has never been drilled into since it is too thick, therefore scientists infer information from observations made on the Earth s surface. In some places, magma from the mantle flows out of active volcanoes on the ocean floor which give scientists information about the composition of the mantle. The mantle is found to have more iron and magnesium and less aluminum and silicon than the crust, therefore the mantle is denser than the crust. The mantle makes up approximately 67% of the Earth s mass and is up to 3000 km thick. The mantle is divided up into three layers based upon the physical characteristics of those layers: The Lithosphere The uppermost part of the mantle which is very similar to the crust is about 100 km thick. In Greek, lithos, means stone. The Asthenosphere This layer below the lithosphere is very hot and has high pressure. It is a softer layer but still solid due to the high temperatures. In Greek, asthenes means weak. The Mesophere Below the asthenosphere, the mesosphere is a strong, solid part that extends to the Earth s core.

4 The Core The core is the layer of the Earth that extends from below the lower mantle to the center of the Earth. Scientists propose that the core is made mostly of iron and contains small amounts of nickel but almost no oxygen, silicon, aluminum, or magnesium. The core makes up approximately 33% of the Earth s mass and has two distinct layers. Outer Core The Earth s outer core is the liquid layer of molten metal that lies beneath the mantle at a very high pressure. Inner Core The Earth s inner core is the solid, dense metallic center at enormous pressures that extends from the outer core to the center of the Earth, 6380 km below the surface. Since the outer core is molten metal and therefore the electrons freely moving in this metal, this layer of the Earth creates a magnetic field. Therefore, the Earth is polar and acts as a large magnet. The strength of the magnetic field of Earth has been reliably and continually measured since From these measurements, we can see that the field s strength has declined by about seven percent since then, giving it a half-life of about 1,400 years (time it takes for the Earth s magnetic field to be cut in half). That means in about 25,000 years, the Earth s magnetic field will be too small to stop and filter harmful solar and stellar radiation and life here would not be able to survive. If one works the clock backwards, more than about 10,000 years ago the Earth s magnetic field would have been so strong the planet would have disintegrated and its metallic core would have separated from its mantle. The energy of the magnetic field is also a support for a Biblical model of creation in that the energy s half-life decays every 700 years. Sea-Floor Spreading In the early 1900s, a scientist named Alfred Wegener wrote about his hypothesis of continental drift. This is the hypothesis that states that the continents once formed a single landmass, broke up, and drifted to their present locations. This hypothesis helped to explain the observation of how well continents fit together as well as why fossils of the same plant and animal species are found on different continents. Wegener called the single, huge continent Pangaea, which is Greek for all earth. Secular scientists predict that Pangaea existed about 245 million years ago applying a Darwinian evolutionary worldview as well as assumptions about constants. They believe that according to the theory of plate tectonics that Pangaea split into two large continents Laurasia and Gondwana about 180 million years ago, and later split into our current continents 65 million years ago. According to a Biblical worldview, the Genesis flood would have easily split the continents from one piece and accelerated the continents away instead of a drifting effect. Many scientific models and observations support this view. A long chain of submerged mountains called mid-ocean ridges run through our oceans. At these mid-ocean ridges, sea-floor spreading takes place. During sea-floor spreading, new oceanic lithosphere forms as magma rises toward the surface and solidifies. As the plates moves away from each other, the sea floor spreads apart and magma fills in the gap. As this new crust forms, the older crust gets pushed away from the mid-ocean

5 ridge. This process of sea-floor spreading with the ocean floors moving like conveyor belts was proposed by an American geologist named Harry Hess. Several types of evidence supported Hess s model of sea-floor spreading: Molten Material Hardened molten material that has erupted has been discovered to be along the midocean ridge. Magnetic Stripes Stripes of oppositely polarized magnetic fields are found along the mid-ocean ridge. Secular scientists believe that the Earth s magnetic field has alternated or reverse during its existence. Drilling Samples Using radioisometric dating, the ages of rocks in samples further away from the ridge were older than the center of the ridges. A Biblical worldview interprets this evidence in support of the Genesis flood where the flood opened up the fountains of the deep (Genesis 7:11) and allowed ferrous (iron)-magnetic material to rise through the existing magnetic field. This caused temporary reversals that rapidly occurred and formed the magnetic stripes at the mid-ocean ridges. There are severe problems with a magnetic field that oscillates and reverses from zero, primarily that if the circulating core fluids decline to zero strength, they would not be able to restart and reverse the orientation. Also, the radioisometric dating does indicate older rocks away from the ridge, but not all dating methods indicate secular dates. Plate Tectonics Plate tectonics is the theory that the Earth s lithosphere is divided into tectonic (Latin for pertaining to building or making) plates that move around on top of the asthenosphere. A boundary is a place where tectonic plates touch. These boundaries are divided into three types: Convergent Boundaries This boundary occurs when two tectonic plates collide. There are continental-continental boundaries, continental-oceanic boundaries, and oceanic-oceanic boundaries within these convergent boundaries. This process is also called subduction and is where the ocean floor sinks beneath a deep-ocean trench and back into the mantle. Divergent Boundaries This boundary occurs when two tectonic plates separate and new sea floor forms. The mid-ocean ridge is the most common type of divergent boundaries. Transform Boundaries This boundary forms when two tectonic plates slide past each other horizontally. The San Andreas Fault in California is a good example of a transform boundary.

6 The motion of tectonic plates may be caused by three possible driving forces: Ridge Push At mid-ocean ridges, the oceanic lithosphere slides downhill under the force of gravity. Convection Hot rock from deep within the Earth rises while the cooler rock near the surface sinks which causes the oceanic lithosphere to move sideways. Slab Pull The denser oceanic lithosphere sinks and pulls the rest of the tectonic plate with it. Modern plate tectonics theory is now mixed with assumptions of uniformity (the belief that rates and constants have always been the same) and ideas of continental drift. Catastrophic plate tectonic models are capable of explaining a wide variety of data including Biblical and geologic data which the slow tectonic theories are incapable of explain. Forces in the Earth s Crust The movement of the Earth s plates creates enormous forces that squeeze or pull the rock in the crust. This force which acts on rock to change its shape or volume is called stress. Energy transfer is what causes the rock to shape or break.

7 There are three different kinds of stress that can occur in the crust: Tension The stress force that pull on the crust, stretching the rock so it becomes thinner in the middle. Compression The stress force that squeezes a rock until it folds or breaks. Shearing The stress force that pushes a mass of rock in two opposite directions. When enough force of stress builds up in a rock, the rock breaks, slides past each other, and creates a fault. Most faults occur along plate boundaries. To properly understand the different types of faults, one must differentiate between a footwall (positive slope) and a hanging wall (negative slope). See the picture below of a footwall and a hanging wall. There are there main types of faults: Normal Faults When a normal fault moves, it causes the hanging wall to move down relative to the footwall. This normally occurs when tectonic forces cause tension that pulls rocks apart. Reverse Faults When a reverse fault moves, it causes the hanging wall to move up relative to the footwall. This normally occurs when tectonic forces cause compression that pushes rocks together. Strike-Slip Faults A strike-slip fault occurs when opposing forces cause rock to break and move horizontally.

8 Sometimes plate movement causes the crust to fold and compress arching upward which are called anticlines (high amplitude), or dipping downward which are called synclines (lower amplitude). This folding has produced large mountain ranges such as the Himalayas in Asian and the Alps in Europe. Other mountains can form through two normal faults running parallel to each other, called a fault-block mountain. Mountains out in the western United States like in the Great Basin resemble this fault-block mountain system. These movements can cause earthquakes, volcanoes, and several other forces of nature seen around the world today. Earthquakes Every day, from the movement of rock beneath the Earth s surface, thousands of earthquakes occur. Although most earthquakes are too small to notice, many can be catastrophic. The force of plate movement increases the potential energy to faults in the rock. Once the potential energy and the stress is too high, an earthquake begins to release a tremendous amount of that stored energy. Deformation, or rock changes in shape, occur in either plastic deformation or elastic deformation. In plastic deformation, energy is lost as is the case in an inelastic collision. In elastic deformation, energy is conserved and much of the energy travels as seismic waves. Seismic waves, or body waves, travel through the Erath s interior in three ways: P Waves Pressure waves or primary waves that travel through solids, liquids, and gases. They move rock back and force (longitudinal) which squeezes and stretches the rock. These p waves are the fastest seismic waves and are the first to be detected. S Waves Shear waves or secondary waves that travel through the rock side to side (transverse). They stretch the rock sideways and therefore cannot travel through parts of the Earth that are completely liquid. They are slower than p waves and arrive later.

9 Surface Waves These waves move along the Earth s surfaced and produce motion in the upper few kilometers of the Earth s crust. Some move up and down and others move back-and-forth. They are slower and much more destructive. Love waves are surface waves that move the ground from side to side damaging foundations of buildings. Rayleigh waves are surface waves that move the ground vertically and horizontally that can affect bodies of water. The epicenter of an earthquake is the point on the Earth s surface directly above the earthquakes starting point. A focus is the point inside the Earth where the earthquake begins. Seismologists are able to find an earthquakes epicenter by using the S-P time method. They collect several seismographs of the same earthquake from different locations first of the P-wave and then the S-wave. They use both curves to determine the earthquake s epicenter. A seismograph can also be used to determine an earthquake s strength, or its magnitude. Mercalli Scale This scale simply described an earthquake s effects. I-III represented people noticing vibrations. IV-VI represented slight damage. VII-IX represented moderate to heavy damage that moves buildings. X-XII represented great destruction, cracks on the ground, and waves on the surface.

10 Richter Scale This scale measures the ground motion from an earthquake divided by the distance. This scale does not work well for large or distance earthquakes. Each time the ground motion increased by a value of 10, the Richter scale increased by one unit. Therefore a 2.0 can only be detected by the seismograph, 4.0 is felt by most people in the area, and a 6.0 can cause widespread damage. Movement Magnitude Scale This system estimates the total energy released by an earthquake. This can be used for all sizes, near and far. This scale includes in its calculation how much movement occurred along the faith, the strength of the rocks that broke when the fault slipped, and the strength of the seismic waves produced. Volcanoes A volcano is a weak spot in the crust where molten material, or magma, comes to the surface. Magma is a molten mixture of rock-forming substances, gases, and water from the mantle. When magma reaches the surface, it is called lava. Volcanoes may form where two oceanic plates collide or where an oceanic plate collides with a continental plate. At a divergent boundary (two oceanic plates colliding), mantle material rises to fill the space opened by the separating tectonic plates. As the pressure decreases, the mantle begins to melt. Because magma is less dense than the surrounding rock, it rises toward the surface, where it forms new crust on the ocean floor. At a convergent boundary (oceanic and continental plate colliding), as the oceanic crust moves downward it becomes hotter and releases water. The water lowers the melting point of rock in the mantle and helps to form

11 magma. When the magma is less dense the surrounding rock, it rises toward the surface. Therefore it is subduction that produces the magma and therefore a volcano. Not all magma develops along tectonic plate boundaries. There are hot spots or places where volcanoes are active that are very far from plate boundaries. Some scientists propose that hot spots are directly above columns of rising magma called magma plumes. Others propose that hot spots are the result of cracks in the Earth s crust. The Hawaiian Islands is an example of a hot spot. Magma is a complex mixture of elements and compounds but its major ingredient is silica (SiO 2 ), one of the most abundant materials in the Earth s crust. The more silica magma contains, the higher its viscosity (or the more resistance to its flow). When high silica content is produced it is too sticky to flow far and it cools to form granite. The low-content silica magma flows readily and forma basalt. There are of course quiet eruptions and explosive eruptions depending upon the amount of silica inside the magma, trapped gases inside the magma, and the pressure inside the pipe. A pyroclastic flow occurs when an explosive eruption hurls out a mixture of hot gases, ash, cinders, and bombs. If the lava cools quickly it forms a smooth, glossy rock named obsidian. If gas bubbles are trapped inside the fast-cooling lava, it forms pumice. Some volcanoes can be active, dormant, or extinct. But when volcanic eruptions create landforms made of lava and ash it can form: Shield Volcanoes Quiet eruptions that gradually build up a gently sloping mountain. Cinder Cone Volcanoes Ash, cinders, and bombs erupt explosively to form a cone-shaped hill. Composite Volcanoes Quiet eruptions alternate with explosive eruptions to form layers of lava and ash. Lava Plateau Made up of many layers of thin, running lava that erupt from along cracks in the ground. Craters A funnel-shaped pit near the top of the central vent of a volcano. Caldera A large, semicircle depression that forms when the magma chamber below a volcano partially empties and causes the ground above to sink.

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