THE ROCK CYCLE 6.2 Weathering breaks down rocks in several ways. Water, wind, and ice cause weathering, as well as repeated changes in temperature (freezing and thawing) will break down rocks over a long period of time. Erosion carries tiny fragments of rocks (sediments) from one place to another. This can be done by blowing wind (sand dunes), flowing water (streams), or moving ice (glaciers). Deposition happens when sediments are dropped by wind, water, ice or gravity. Three types of rock are: - Sedimentary – formed by sediments getting pressed and cemented together. - Metamorphic – formed by extreme heat and pressure over time. - Igneous – formed when magma or lave cools. The rock cycle happens when each type of rock becomes the other 2 types by going through their formation process. Examples: An igneous or metamorphic rock that breaks down into tiny pieces can get pressed and cemented together into a sedimentary rock. A sedimentary or metamorphic rock can melt and cool into an igneous rock. An igneous or sedimentary rock can get heated and pressed into a metamorphic rock. Subsidence – when an area of land sinks to a lower level than the surrounding areas. Uplift – when an area of land is lifted to higher elevations than the surrounding areas. Rift zone – an area of land where tectonic plates are pulling apart and creating cracks. EARTH’S LAYERS 6.3 The Earth’s layers can be divided in 2 ways; by their chemical composition, and by their physical properties. Compositional layers are the crust, mantle and core. - The crust is the outermost and thinnest layer. It contains oxygen, silicon, and aluminum. - The mantle is a region of hot, slow-flowing rock. Convection takes place here. It contains the same minerals as the crust, plus magnesium. - The core is the center of Earth. It is very dense, and is composed mostly of iron and nickel. Physical layers are the lithosphere, asthenosphere, mesosphere, outer core, and inner core. - The lithosphere is made of the crust, and the rigid, upper part of the mantle. It is broken into large pieces called tectonic plates. - The asthenosphere is soft like pudding. The tectonic plates move on top of this layer. - The mesosphere is the strong middle part of the mantle. - The outer core is the liquid layer of the core. - The inner core is the solid layer of the core. PLATE TECTONICS 6.4 Plate tectonics, originally called continental drift, describes how large pieces of Earth’s outermost layer slowly move and change shape. There are about 12 major plates, with each one containing large pieces of the lithosphere beneath its crust. There are 3 types of boundaries around plate edges. - Convergent – two plates collide, creating mountains. - Divergent – two plates move away from each other. - Transform – two plates slide past each other. Tectonic plates move in 3 ways. - Mantle convection – hot magma rises, cools and sinks, dragging the tectonic plate above it. - Ridge push – new magma on the surface cools and moves down the slope away from the ridge, pushing the rest of the plate down and away. - Slab pull – as the tectonic plate moves farther from the ridge, the weight of the sinking plate drags the rest of the plate downward.