Science Notes Sheet (Earth's Layers) PDF

**Science Notes Sheet** **Earth\'s Layers -- structure and composition.** Mantle Going deeper just underneath the crust we next encounter the mantle. The mantle extends to a depth of 85% of the total weight and mass of the Earth. The mantle is composed of silicate rocks that contain a lot of appr...

**Science Notes Sheet** **Earth\'s Layers -- structure and composition.** Mantle Going deeper just underneath the crust we next encounter the mantle. The mantle extends to a depth of 85% of the total weight and mass of the Earth. The mantle is composed of silicate rocks that contain a lot of approximately 2 900 km from the surface and is made of a thick, solid, rocky substance that represents about iron and magnesium. These solid rocks are so hot that they can flow slowly from one place to another. The average temperature of the mantle is about 2 000°C. This is also where most of the internal heat of the Earth is generated and circulated by large convection currents. OUTER CORE Travelling deeper within the Earth, we next would encounter the Earth\'s outer core, which extends to a depth of around 5 100 km beneath the surface. It is believed that this outer core is made up of super-heated liquid molten lava. This lava is believed to be mostly made from the elements iron and nickel at a temperature of about 4 500°C. INNER CORE Finally, we reach the Earth\'s inner core. The centre of the Earth in the middle of the inner core is about 6 400 km from the surface. It is believed that this inner core is a solid ball composed of mostly iron at a temperature of about 6 000°C. The inner core is thought to rotate at a different speed relative to the rest of the Earth and this is thought to contribute to the Earth\'s magnetic field. LITHOSPHERE The lithosphere is a name that scientists use to describe the solid outer shell of a planet. The Earth\'s lithosphere is made up of the crust and the upper part of the mantle and is about 100 km thick. The lithosphere is broken into large sections called tectonic plates, which are constantly moving. The speed of movement is similar to fingernail growth which is between 1 cm and 10 cm per year. ASTHENOSPHERE The asthenosphere is the lower part of the mantle. The asthenosphere temperature is 300-500°C. The asthenosphere is ductile and can be pushed and deformed like silly putty in response to the warmth of the Earth. These rocks actually flow, moving in response to the stresses placed upon them by the motions of the deep interior of the Earth. The flowing asthenosphere carries the lithosphere of the Earth, including the continents, on its back.\ Tectonic Plates and Theories -- including the evidence for plate tectonics. **\ Tectonic Plate Movement -- how plates move and what drives this movement.** The theory that Earth\'s outer layer is made up of large, moving plates. Evidence for the theory of plate tectonics is continental drift, appearance of younger crustal layers in the ocean, earthquakes along plate boundaries called fault lines, the presence of similar fossils and rocks on separate continents, and the matching shapes of continents that once fit together as a larger continent. The pattern of earthquakes and volcanoes along plate boundaries. Seafloor Spreading, the process by which new oceanic crust forms at mid-ocean ridges. Convection Currents: The movement of molten rock in the lower mantle, asthenosphere, which drives plate movement. **\ Three Tectonic Boundary Types and Their Interactions -- convergent, divergent, and transform boundaries, and what happens at each type.** Convergent Boundaries: Where two plates collide. - Continental-Continental: Mountain ranges (e.g., Himalayas). - Oceanic-Continental: Subduction zones and volcanic arcs (e.g., Andes Mountains). - Oceanic-Oceanic: Volcanic Island arcs and deep-sea trenches (e.g., Mariana Trench). Divergent Boundaries: Where two plates move apart. - Mid-Ocean Ridges: New oceanic crust forms. - Continental Rifts: Can lead to the formation of new ocean basins (e.g., East African Rift Valley). Transform Boundaries: Where two plates slide past each other. - Earthquakes: Frequent earthquakes occur along these boundaries (e.g., San Andreas Fault). **\ Minerals -- their properties and significance.** Properties: Colour, lustre, hardness, streak, cleavage, size of crystal. Significance: Minerals are the building blocks of rocks, and their significance in rocks is that they give rocks their structure, composition, and name **\ Three Rock Types and Their Formation -- igneous, sedimentary, and metamorphic rocks.** Igneous Rocks: Igneous rocks are formed when liquid or molten rock cools and solidifies. The inside of the Earth is hot enough to melt rocks. Molten (liquid) rock forms when rocks melt. The molten rock is called magma. When the magma cools and solidifies, a type of rock called igneous rock forms. Igneous rocks contain randomly arranged interlocking crystals. The size of the crystals depends on how quickly the molten magma solidified. The more slowly the magma cools, the bigger the crystals are. If the magma cools quickly, small crystals form in the rock. This can happen if the magma erupts from a volcano. Obsidian and basalt are examples of this type of rock. They are called extrusive igneous rocks because they form from eruptions of magma. Basalt is an example of an extrusive igneous rock with small crystals. Basalt is often found around volcanoes as a result of an eruption. Intrusive: Cool slowly underground (e.g., granite). Extrusive: Cool quickly on the surface (e.g., basalt). Sedimentary Rocks: A river carries, or transports, pieces of broken rock as it flows along. When the river reaches a lake or the sea, its load of transported rocks settles to the bottom. We say that the rocks are deposited. The deposited rocks build-up in layers, called sediments. This process is called sedimentation. The weight of the sediments on top squashes the sediments at the bottom. This is called compaction. The water is squeezed out from between the pieces of rock and crystals of different salts form. The crystals form a sort of glue that sticks or cements the pieces of rock together. This process is called cementation. The oldest layers are at the bottom and the youngest layers are at the top. Sedimentary rocks may contain fossils of animals and plants trapped in the sediments as the rock was formed. - Clastic: Composed of rock fragments (e.g., sandstone). - Chemical: Formed from minerals precipitating from solution (e.g., limestone). - Organic: Formed from the remains of organisms (e.g., coal). Metamorphic Rocks: Formed from the alteration of existing rocks by heat or pressure. Earth movements can cause rocks to be deeply buried or squeezed. As a result, the rocks are heated and put under great pressure. They do not melt, but the minerals they contain are changed chemically, forming metamorphic rocks. Sometimes, metamorphic rocks are formed when rocks that are close to some molten magma get heated up. Metamorphic rocks are formed from layers of sedimentary rocks that are put under pressure and heated up by magma. Metamorphic rocks form close to magma chambers, but not close enough to melt. Remember that metamorphic rocks are not made from melting rock. Rocks that do melt form igneous rocks instead. When a metamorphic rock is formed under pressure, its crystals become arranged in layers. Slate, which is formed from shale, is like this. Slate is useful for making roof tiles because its layers can be split into separate flat sheets. Marble is another example of a metamorphic rock. It is formed from limestone. Metamorphic rocks can be formed from any other type of rock - sedimentary or igneous. - Foliated: Have a layered appearance (e.g., slate, schist, gneiss). - Non-Foliated: Do not have a layered appearance (e.g., marble, quartzite). **\ The Rock Cycle -- processes and transitions between rock types.** The Earth\'s rocks do not stay the same forever. They are continually changing because of processes such as weathering and large earth movements. Weathering is the breakdown of rocks on the Earth\'s surface by the action of rainwater, extremes of temperature and biological activity. There are three main types of weathering: physical, chemical and biological. Physical weathering is caused by the effects of changing temperature on rocks, causing the rock to break apart. The process is sometimes assisted by water. Physical weathering happens especially in places where there is little soil and few plants growing, such as in mountain regions and hot deserts. It occurs through repeated melting and freezing of water (mountains and tundra) or through expansion and contraction of the surface layer of rocks that are baked by the sun (hot deserts). There are three main types of physical weathering. Temperature change If a rock is heated and cooled many times, cracks form and pieces of rock fall away. When the rock is heated it expands and when it cools it contracts. Freeze-thaw Water expands when it freezes into ice. If water gets into a crack in a rock and then freezes, it expands. As it freezes, it pushes the crack apart. Eventually the ice will melt and leave the crack larger than before. The process of freezing and thawing can continue until the crack becomes so big that a piece of the rock falls off. Exfoliation Wind, rain, and waves can all cause weathering. The wind can blow tiny grains of sand against a rock. This process can wear the rock away. Rain and waves can also wear away rock over long periods of time through erosion. Chemical weathering is caused by rainwater reacting with the mineral grains in rocks to form new minerals (clays) and soluble salts. These reactions occur particularly when the water is slightly acidic. These chemical processes need water, and occur more rapidly at higher temperature, so warm damp climates are best. Chemical weathering (especially hydrolysis and oxidation) is the first stage in the production of soils. BIOLOGICAL WEATHERING Living organisms contribute to the weathering process in many ways: Trees put down roots through joints or cracks in the rock in order to find moisture. As the tree grows, the roots gradually prize the rock apart. Many animals, such as the Piddock shells in the photo below, bore into rocks for protection either by scraping away the grains or secreting acid to dissolve the rock. Even the tiniest bacteria, algae and lichens produce chemicals that help break down the rock on which they live, so they can get the nutrients they need. Living organisms contribute to the weathering process in many ways: Trees put down roots through joints or cracks in the rock in order to find moisture. As the tree grows, the roots gradually prize the rock apart. Many animals, such as the Piddock shells in the photo below, bore into rocks for protection either by scraping away the grains or secreting acid to dissolve the rock. Even the tiniest bacteria, algae and lichens produce chemicals that help break down the rock on which they live, so they can get the nutrients they need. The rocks are gradually recycled over millions of years. This is called the rock cycle.  For example, sedimentary rocks can be changed into metamorphic rocks which can be weathered and the pieces transported away. These pieces could be deposited in lakes or seas and eventually form new sedimentary rock. Many routes through the rock cycle are possible.