Chapter 4 ROCKS “The Mixture of Minerals”
Rock – a naturally occurring solid mixture of crystals of one or more minerals. • Rock Cycle – the continual process by which new rock forms from old rock material. • Rocks are always changing. The Rock Cycle
Weathering – the process in which water, wind, ice, and heat break down rock. • Weathering is very important: • Breaks down rock into fragments called sediment. • The fragments are the materials that are used to make sedimentary rocks. Weathering, Erosion, and Deposition
Physical Weathering – Any process in which rocks are broken down by contact with the Earth’s atmosphere and water. • Chemical Weathering – Occurs when chemical reactions break down the bonds holding the rocks together. • Most common in areas that contain large amount of water. Types of weathering
Erosion – the process by which sediment is removed from its source. • Different types of erosion: • Wind • Ice • Water • Gravity Weathering, Erosion, and Deposition
Deposition – the process in which sediment moved by erosion is dropped and comes to rest. • Once deposited, sediments may be compressed and cemented to form a sedimentary rock. Weathering, Erosion, and Deposition
Heat and pressure may cause a rock to chemical change into a metamorphic rock. If the rock gets too hot it will melt which eventually cools to form igneous rocks. Heat and Pressure
Foliation – The set of layers visible in many metamorphic rocks as a result of flattening and stretching of mineral grains during metamorphism. Foliation
Bedding – layers of sedimentary rock. • This can also be referred to as strata. Bedding
The relationship of heat and pressure: Heat and Pressure • ^Pressure ^ Heat • ^ Heat ^ Pressure
Gravitational Potential Energy – is the potential energy associated with gravitational forces, as work is required to elevate objects against Earth’s gravity. Mechanical energy
Rock is exposed at the Earth’s surface by a combination of uplift and erosion. • Uplift – is the movement within the Earth that causes rocks inside the Earth to be moved to the Earth’s surface. • After uplift, the rock reaches the surface, and the cycle continues. How the Cycle Continues
You are going to need your notebook for this activity. In the output section record 10 rolls of the dice. (Write down what the dice said.) You may never move from a station but continue to roll the dice at that station and write down what the dice said. Once you have finished return to your seat. A Trip around the rock cycle
Three main classes of rock: • Igneous • Sedimentary • Metamorphic In order to identify rocks scientist break the rocks up into two categories: Composition and Texture Rock Classification
Composition – the chemical makeup of a rock; describes either the minerals or other materials in the rock. • Determined by the minerals contained in the rock. • Ex. A rock made of mostly the mineral quartz will have a composition very similar to that of quartz. Composition
Texture – is the quality of a rock that is based on the sizes, shapes, and positions of the rock’s grains. • There are three different grains of texture: • Fine-grained • Medium-grained • Coarse-grained Texture
The amount of time that a igneous rock is allowed to cool determines the texture of the rock. • If the rock cools quickly then it will be fine grained. • If the rock cools slowly then it would be coarse grained. • The texture of a rock can reveal the processes that formed it. Texture
Your assignment: Create a children’s story, comic strip, or some other creative story about Roger the Rock. Roger is a rock that has been a part of the rock cycle for millions of years. Your job is to tell Roger’s story. You must describe how Roger was “born” and at least three transitions that occurred during Roger’s life. (For example, changing from igneous to sedimentary, sedimentary to metamorphic, and metamorphic to igneous.) Your grade will be based on in-class work, the accuracy of your information, creativity, and neatness/effort. This should be a story appropriate for a children’s story (think back to 2nd grade here!), including pictures. To earn an “A”, you need to include many details-the names of specific rock types, descriptions about what causes the changes to occur, etc. This project will be due on the day of Chapter 4 Test. These projects will be presented by you and your partner. ROGER THE ROCK
Mantle Convection – the slow creeping motion of Earth’s rocky mantle caused by convection currents carrying heat from the interior of the Earth to the surface. • Convection Currents – the uneven heating of rock in the Earth’s asthenosphere that causes rock to rise and sink. Mechanisms that drive lithospheric plates
Ridge Push – Gravitational force that causes a plate to move away from the crest of an ocean ridge, and into a subduction zone. Mechanisms that drive lithospheric plates
Gravity Pull/Slab Pull – another force where the weight of a sub-ducting slab pulls the plate at the surface down. • Colder ocean plates are denser. Gravity Pull
Wegener’s Continental Drift Hypothesis • Continental drift – the hypothesis that states that the continents once formed a single landmass, broke up, and drifted to their present locations. • Alfred Wegener proposed the theory in the early 1900’s.
Wegener’s Continental Drift Hypothesis • Supporting Evidence • Plates Fit together like a puzzle. • Fossil Evidence across continents. • Rocks matched across seas. • Glacial striations on rocks matched on Africa and South America proving a once super continent. • Coal on Antarctica proves that it was once warm.
Wegener’s Continental Drift Hypothesis • Inconclusive Evidence • No credible evidence that explained why the continents moved. • Wegner thought that the continents just “plowed” through the rocks. • Many scientist concluded that the continents would have broken into several different pieces if this were to true.
The Drifting Continents • 245 million years ago • Pangaea (Means entire Earth) existed when some of the earliest dinosaurs were roaming the Earth. • Panthalassa (all sea) The ocean that once covered the Earth.
The Drifting Continents • 180 Million Years ago Pangaea gradually breaks up into two pieces. • Laurasia • Gondwana
The Drifting Continents • 65 million years ago. • Dinosaurs became extinct and Laurasia and Gondwana split into two smaller pieces.
Mid-Ocean Ridges and Sea-Floor Spreading • Sea-floor spreading – the process in which new oceanic lithosphere forms as magma rises toward the surface and solidifies. • A chain of submerged mountains runs through the center of the Atlantic Ocean. • Also known as Mid-ocean Ridges
Mid-ocean ridges and Sea-Floor Spreading • As tectonic plates move away from each other, the sea floor spreads apart and magma fills in the gap. • New crust forms, older crust gets pushed away from the mid-ocean ridge.
Evidence for Sea-Floor Spreading: Magnetic Reversals • Biggest evidence comes from magnetic reversals recorded in the ocean floor. • North and South poles have changed places many times. • Magnetic Reversal – the process in which magnetic poles change places.
How magnetic reversal works. • Tiny grains of magnetic minerals are found at the mid-ocean ridges. • Mineral grains contain iron and are like compasses. • They align with the magnetic field of the Earth. • When the rock cools, the record of theses tiny compasses remains in the rock.
Magnetic Reversals and Sea-Floor Spreading • Rock is slowly taken away from the spreading center of the ridge as sea-floor spreading occurs.
Seafloor Spreading • Activity on seafloor spreading.
The Theory of Plate Tectonics • Plate Tectonics – the theory that explains how large pieces of the Earth’s outermost layer called tectonic plates, move and change shape.
Tectonic Plate Boundaries • Boundary – a place where tectonic plates touch. • There are three different types of boundaries: • Convergent • Divergent • Transform
Convergent Boundaries • Convergent Boundary – the boundary formed by the collision of two lithospheric plates. • There are three different types of convergent boundaries: • Oceanic – Oceanic • Oceanic – Continental • Continental - Continental
Oceanic – Oceanic Plate Boundaries • http://geology.com/nsta/convergent-boundary-oceanic-oceanic.gif
Oceanic – Oceanic Convergent Boundary • Normally one of the oceanic plates will subduct below the other. • The older plate is usually the one that gets pushed down because it has a greater density. • Eventually magma is formed because of the increased pressure causing volcanoes to form over the top of the layer. • Eventually the volcanoes will peak out of the water and if they continue to grow the will form island chains. • Ex. Japan