Grade 7 Exam Guide PDF

Weathering and erosion Weathering • The physical and chemical processes that break rocks down Physical weathering • Weathering can happen because of: • • • • • Temperature change Water and ice Crystallization of salts Wind Living plants Temperature • Solids expand when they are heated and con...

Weathering and erosion Weathering • The physical and chemical processes that break rocks down Physical weathering • Weathering can happen because of: • • • • • Temperature change Water and ice Crystallization of salts Wind Living plants Temperature • Solids expand when they are heated and contract when they are cooled. • The same happens with rocks except this can crack rocks Ice and water • Can split rocks by freezing water • As the ice expands it widens cracks in rocks Salts • As salts crystalise in rocks they weather them Glaciers • They are like frozen rivers of ice that move along valleys very slowly • As they move, the ice scrapes pieces off the surrounding rocks, forming valleys that are U shaped Water • Water running or washing over rock can also wear them away Wind • Fine particles of rock carried blast the rock surface Plants • Plants growing through rocks can split them Chemical weathering • Involves water and chemicals in the water and air reacting with the rock and changing it • E.g. dolerite reacting with Oxygen. The iron in it forms Rust and as it does it doesn’t hold the dolerite together acid • Acid rain which contains dissolved acids can dissolve the rock Erosion • Small particles of rock broken off by weathering can be carried away by water, wind and ice • The removal of rock particles is called erosion Plate tectonics Year 7 Science Continental Drift In 1915, Alfred Wegener claimed that the Earth’s continents were once connected to each other and that over time the continents had separated and drifted apart. Continental Drift He called the single supercontinent Pangaea. Which over time split into two land masses, Laurasia (the northern continent) and Gondwana (the southern continent) Evidence of Continental Drift Wegener based his conclusions on two main observations. - The continents seemed to fit together like a jigsaw puzzle That fossils of the same species were found on continents that were a long way apart. What we know now. The Earth is made up of different layers. Each with different properties Earth’s Layers Tectonic plates The crust is made up of a number of moveable lithospheric plates sitting and moving along the molten asthenosphere below What scientific evidence do we have that these cracks in the crust exist? Seafloor spreading Studies of the ocean floor discovered the presence of large underwater mountain ridges running around the Earth. These ridges were found to have huge series of rifts (cracks) in their centres. It has been described as the Great Global Rift System, Great Global Rift System Seafloor spreading Seafloor spreading Harry Hess, an American geologist proposed that new rocky crust was being formed at the ocean ridges and spreading outwards. He also proposed that the crust was sinking down into the Earth in ocean trenches through the process of subduction. When combined, seafloor spreading and subduction are involved in the creation and destruction of the crust. Seafloor spreading The symmetry of the rock on either side of the sea floor suggests it must have a crack Magnetic striping Through seafloor spreading, new rock is deposited in strips. When this new rock is formed, particles in the rock called magnetite align with the magnetic poles of the Earth, just like a compass needle. Every few million years, the Earth’s magnetic fields reverse (North becomes South etc) When this happens, the direction that the magnetite particles align also reverse. This causes a pattern of magnetic striping as new rock is formed. Magnetic striping How plates move Theory 1: Convection Currents Convection currents in the mantle ● ● As magma in the mantle is heated, it becomes less dense and rises. Once it reaches the crust the magma then travels along the underside of the solid crust until it cools down, becoming more dense. This causes the magma to sink back down. This movement of magma is thought by some scientists to play a role in the movement of the continents. How plates move Theory 2: Ridge push and slab pull Types of crust Oceanic crust ● ● ● ● ● 5 – 10 km thick More dense Tiny Crystals Very hard rock Contains heavier elements e.g. iron, magnesium Continental crust ● 25 – 100 km thick ● Less dense ● Larger crystals ● More easily eroded ● Contains lighter elements e.g. aluminum, silicon Type of plate movement Minerals Earth and Space Science Defining a Mineral • A mineral is a naturally occurring inorganic solid, with a definite chemical composition, and an ordered atomic arrangement. Breaking down the definition • Minerals are naturally occurring…………………..They are not made by humans • Minerals are inorganic…..They have never been alive and are not made up from plants or animals • Minerals are solids………….They are not liquids (like water), or gases (like the air around you) • Minerals have a definite chemical composition They have a formula • Minerals have an ordered atomic arrangement…..The chemical elements that make up each mineral are arranged in a particular way - this is why minerals 'grow' as crystals There are substances that have most of the criteria for minerals and are called mineralloids → Example: Opal – does not have an orderly arrangement of atoms How many minerals are there? • 3500 known minerals in the Earth’s crust • Only 20 minerals combine to form 95% of all rocks on Earth. The Physical Properties of Minerals • All minerals have physical properties that can be used to define, describe, and identify them as unique minerals 1. Colour – Some minerals are always the same colour. Malachite and azurite are both copper minerals. Malachite and azurite can be found together, but malachite is always green, azurite blue 1. Colour – But many minerals can be a variety of colours. Fluorite for instance can be lots of different colours. The different colours are caused by the slight imperfections or impurities a mineral may contain. To identify many minerals you must look at more than just their colour. 2. Lustre Luster refers to the way the mineral reflects light Eg. Glassy – reflects light like a piece of glass Metallic – reflects light like a piece of metal Dull – does not reflect light well And others… 3. Streak – The streak of a mineral is the color of the powder produced when it is dragged across a surface. The color could be different from the minerals color, and is always distinctive Many minerals do not have a streak 4. Hardness • Hardness is the resistance of a mineral to scratching. • It is a property by which minerals may be described relative to a standard scale of 10 minerals. This is known as the Mohs scale of hardness. Mohs scale of hardness • In 1812, Friedrich Mohs – famous geologist and mineralogist created a scale of mineral hardness grading from the softest (1) to the hardest (10). The scale was created using the simple technique of one mineral's ability to visibly scratch another Moh’s Hardness Scale 5. Crystal shape Minerals can be identified by the shape of their crystals. The shapes of crystals are determined by a number of factors such as the size and length of their surfaces (known as 'faces') and edges, as well as the angles between these. These shapes are named after their geometry - for example crystals based on cubes belong to the cubic crystal group. 6. Mineral Cleavage – Cleavage is the way a mineral breaks/splits along definite crystallographic structural planes. Cleavage can be in one plane or multiple planes. Minerals can have no cleavage (eg quartz) 7. Fracture Fracture is the property of a mineral breaking in a more or less random pattern. Minerals with no cleavage generally break with irregular fracture called a concoidal fracture Metamorphic Rocks How a little bit of heat & pressure transform rocks! What is a metamorphic rock? • The term "metamorphic" means "to change form." • Any rock (igneous, sedimentary, or metamorphic) can become a metamorphic rock. If rocks are buried deep in the Earth at high temperatures and pressures, they form new minerals and textures all without melting. If melting occurs, magma is formed, starting the rock cycle all over again. Metamorphic Rock Types • There are two types of metamorphic rocks. • Each is classified according to its composition and texture. • Foliated • Nonfoliated. Summary Summary VOLCANOES AND IGNEOUS ROCKS VOLCANOES  http://www.youtube.com/watch?v=Be7o6BYVOzA  Definition of Volcano ▪ Mountain that forms when molten rock (magma) is forced to the Earth’s surface STRUCTURE OF A VOLCANO FORMATION OF VOLCANOES The Formation of Magma • Mantle rock melts when the temperature increases or the pressure decreases. FORMATION OF VOLCANOES  Temperatures in the mantle are hot enough to melt rock into magma.  Less dense than the solid rock around it, magma rises and some of it collects in magma chambers.  As the magma rises, pressure decreases allowing trapped gasses to expand and propel the magma through the openings in the Earth’s surface causing an eruption.  Erupted magma is called lava. WHAT ARE IGNEOUS ROCKS?  Ignis = fire in Latin  So…  Igneous rocks are rocks that have formed when molten material from within the Earth cools and becomes solid.  Molten material is called Magma when it is below the ground and Lava when it is above the ground.  Magma reaches the Earth’s surface when volcanoes erupt.  When magma is solidifying, particles in the liquid may clump together to form structures called crystals.  Crystals are solids that have special shapes. IGNEOUS ROCKS CHARACTERISTICS OF IGNEOUS ROCKS  Hard: Because the minerals they contain are hard  Strong: Because the mineral crystals that make them are strong  Made of interlocking cr ystals that have grown into each other and lock together.  Igneous rocks are classified according to how they were formed and the texture and colour of the rock. Minerals ◆ Are the building blocks of rocks ◆ Have a (very complex) chemical formula ◆ Examples are – Quartz – Mica – Feldspar Mineral Characteristics ◆ Crystal structure ◆ Lustre – how light reflects ◆ Pigment and streak – what colour it ‘draws’ on a tile ◆ Hardness Types of rocks: Sedimentary ◆ Formed from weathered sediment ◆ Transported and deposited and compacted ◆ Course or fine grained according to speed of transporting medium ◆ Sharp or rounded particles depending on how much they are ‘rubbed’ during transit. ◆ Eg, Sandstone, conglomerate, shale Types of rocks: Metamorphic ◆ Formed when any type of rock is stressed and ‘cooked’ under heat and pressure. ◆ Causes rocks to ‘laminate’ into layers ◆ Caused rocks to harden. ◆ Shale becomes slate. The rock cycle ◆ Describes how rocks do not disappear but are gradually recycled over millions of years. Fossils ◆ Provide a record of past life ◆ Casts, molds, hardened body parts, footprints ◆ Formation: death, cover, petrified, uplifted, eroded ◆ Older fossils are lower, younger fossils are in higher rock layers ◆ Dinosaurs – how did they become extinct? Life Cycle of a Star Overview Stage 1 Protostars Protostars • Huge clouds of gas (hydrogen) in which stars are made. • Many thousands of times bigger than our solar system • As the clouds collapse stars are born in them Stage 2 Main sequence star Main Sequence Star • E.g. Our Sun • Sequence lasts for about 10 000 million years • Our Sun is about half way through it’s main sequence Stage 3 Red Giant Red Giant • As the sun runs out of hydrogen the outer layers of the sun will become cooler • They will also expand massively. • The Earth (along with Mercury, Venus and Mars) will be swallowed up. Stage 4 White Dwarf White Dwarf • Gravity will cause the red giant to collapse • The sun is now much cooler and it collapses into a small white star • It still has the same mass as the original sun! Stage 5 Black Dwarf Black Dwarf • The sun cools more and more • Eventually it will become a black mass emitting no light • It will then spend the rest of eternity drifting silently through space Stars bigger than our sun! At least four times bigger Stage 4 (for a big star) Red Supergiant Stage 5 (for a big star) Supernova Supernova! • The largest and most powerful explosions in the universe. • The red supergiants literally blow themselves apart! Supernova • All the atoms we are made from came originally from these giant supernova explosions. Stage 6 (for a big star) Black hole Black hole • After the supernova a huge mass is left behind. • There is so much mass its gravity prevents even light from leaving it • Black holes can suck in nearby stars and solar systems.