Slideshow Transcript

1. Slide 1: Science Interactive LTD Copyright 2005 Science Interactive LTD Multimedia CD-ROM for PC is a collection of 38 units totalling over 1150 PowerPoint slides matched to current single and double Science GCSE syllabuses. Each unit covers a wide range of different delivery and learning styles, offering an exciting way to involve your pupils during lessons or revision sessions. All styles of teaching and learning are supported through use of high quality images, graphics, challenging exercises and questions. Units can be used in the classroom via an interactive whiteboard, data projector or used during individual study via a PC or school network. Full users’ licence is available under our ‘comprehensive package’ or lessons can be purchased separately. Science Interactive LTD. PO BOX 50764 LONDON NW6 9AT email: sales@science-interactive.co.uk web: www:science-interactive.co.uk GCSE SCIENCE Unit 1: The Digestive System Unit 20: Crude Oil and its Products Unit 2: The Circulatory System Unit 21: Rock Cycle OCR Unit 3: Healthy Body and Immunity Unit 22: Elements, Molecules and Compounds EDEXCEL AQA Unit 4: The Respiratory System Unit 23: Ionic and Covalent Compounds Unit 5: Nervous System and the Senses Unit 24: The Halogens, their Uses and Compounds Unit 6: Human Homeostasis Unit 25: The Noble Gases, their Properties and Uses Unit 7: Hormones and the Endocrine System Unit 26: Rates of Reaction Unit 8: Drugs and Bad Body Maintenance Unit 27: Energy Unit 9: Photosynthesis in Green Plants Unit 28: Generating Electricity and its Domestic Use Unit 10: Water Transport in Plants Unit 29: Electricity Unit 11: Flow of Energy and Elements through the Environment Unit 30: Light and the Electromagnetic Spectrum Unit 12: Mitosis and Meiosis Unit 31: Radioactivity Unit 13: Inheritance and Selection Unit 32: Newton's Forces and the Effects of Forces Unit 14: Evolution and Human Impact Unit 33: Earth and Space Unit 15: Genetic Engineering Unit 34: The Earth and Plate Tectonics Unit 16: The Periodic Table and its Elements Unit 35: The Alkaline Earth Metals Unit 17: The Alkali Metals Unit 36: Sound and Hearing Unit 18: Metals and their Properties Unit 37: Natural Forces Unit 19: The Transitional Metals Unit 38: Cells, Tissue, Organs and Organs systems
2. Slide 2: Science Interactive LTD Copyright 2005 Earth 149,600,000km Distance from the sun: Igneous Sedimentary Metamorphic Planet radius: 6,378km Planet volume: 970,400,000,000 km3 Planet mass: 5972,500,000,000,000,000,000,000 kg Planet moons: One Planet orbit: 365 days Surface temperature: +18oC Unit 21  Rock Cycle 
3. Slide 3: Unit 21: Rock Cycle Science Interactive LTD Copyright 2005 Understand: Keywords: The nature of the Earth’s crust. 1. Rocks, Cycle, Formation, Erosion, Breakdown, That rocks contain different types of minerals 2. Sedimentary, Igneous, Metamorphic, which are formed by elements joining together. Sediments, Fossils, Properties, Minerals, That there are three rock types: sedimentary, 3. Elements, Calcite, CaCO3, Weathering, igneous and metamorphic. Physical, Chemical & Biological. That these are grouped because of how they are 4. formed. That fossils are only found in sedimentary rocks. 5. The main uses of the mineral calcite (CaCO3) in 6. cement, concrete and glass manufacture. That the rock cycle is a continuous process of 7. rock formation and breakdown. That there are different types of weathering; 8. Physical, Biological and Chemical. That erosion can lead to further breakdown of 9. sedimentary, metamorphic and igneous rocks. Click mouse to begin Science Interactive LTD PO BOX 50764 LONDON NW6 9AT web: www.science-interactive.co.uk email: sales@science-interactive.co.uk
4. Slide 4: Science Interactive LTD Copyright 2005 The Earth’s crust The Earth’s crust ranges from 5 to 65 kilometres thick. About 30% of the Earth’s crust lies above the great oceans and seas. It is extremely important for human survival, with its top layer of n________ rich soil, its minerals and metal ores. A mineral is any solid substance that is rich in elements like iron, silicon and oxygen. Rocks are complex mixtures of minerals containing many different e___________, chemically joined together. The main elements in the Earth’s crust are oxygen, silicon, aluminium and iron. Name three metal ores found in Earth’s crust ? Earth’s crust: Word bank: nutrient elements Earth The Earth’s surface Diagram Element Symbol Percentage Element Symbol Percentage Notes Oxygen O 47% Calcium Ca 3.5% Silicon Si 28% Sodium Na 3% Aluminium AL 8% Potassium K 2.5% Iron Fe 5% Magnesium Mg 2%
5. Slide 5: Science Interactive LTD Copyright 2005 Earth’s elements, minerals and rocks The Earth’s crust is a collection of elements like o_________, silicon, aluminium and iron. Elements are bound together forming different minerals. These minerals are the building blocks of sedimentary, i__________ and metamorphic rocks. Minerals found in all types of rocks are continuously recycled over hundreds of millions of years as surface rocks are worn away to be replaced by new rocks forced up by tectonic plate movements. Show how sedimentary rocks are formed from the remains of eroded surface rocks ? Minerals and rocks: Word bank: oxygen igneous Elements Minerals Types of rock Igneous Diagram Sedimentary Metamorphic Metamorphic Elements only contain one type of atom and are pure substances. Minerals like calcite (CaCO3) and quartz Notes (SiO2) form when water is forced out, leaving behind these compounds. All rock types contain a high percentage of metallic salts. Marble is made mostly from the mineral calcite (CaCO3)
6. Slide 6: Science Interactive LTD Copyright 2005 The rock cycle The rock cycle is a continue process of rock formation and breakdown. The three types of rocks s____________, igneous and metamorphic are recycled in this way over many millions of years. The movement of the Earth’s plates, which is driven by the convection currents inside its mantle causes uplift and burying of all three types of rocks. At the p_______ boundaries, geographical features like mountains or trenches are formed. The rock cycle: Word bank: sedimentary plate continental crust Inside the Earth Er ift os pl io U n Pr es su re Up lif t Sedimentary Igneous He at a lift nd Up pre ssu The movement of the plates re Up is driven by the convection re lift su currents deep inside the es co pr ol in Earth's mantle. At plate d an g boundaries mountains or at Magma Metamorphic He trenches form due to the Heat huge pressures involved.
7. Slide 7: Science Interactive LTD Copyright 2005 Formation of the Earth’s rocks All three rocks types that make up the five continental plates are continually formed and broken down by chemical, p_________ and biological weathering. Their origins and how they are formed are very different giving them their own unique properties. Follow the diagrams and explanations below and learn the starting materials and how each type of rock is formed (sedimentary, igneous & metamorphic) Rock formation: Word bank: physical Rock Sedimentary Igneous Metamorphic Starting materials Notes Any rock type that is eroded by Igneous rock is formed when Metamorphic rock forms when chemical, physical and biological buried rock is heated forming either igneous or sedimentary rock weathering can lead to the formation magma. Molten magma rock is buried. High temperatures and of sediments. These sediments begin rises to the Earth’s surface pressure cause the crystals to to form layers which are then through cracks and then cools realign giving the new rock very subjected to compacting over time. forming igneous rock. different properties Sedimentary Igneous Metamorphic Formed rock
8. Slide 8: Science Interactive LTD Copyright 2005 Sedimentary rock formation one The Earth’s surface rocks are continuously eroded away by physical and chemical weathering. These weathered r_______ and other small rock fragments begin to settle as sediments on the bottom of lakes, seas and oceans. With time these layers accumulate. Pressure on the lower layers cause these particles to compact and bond together. Water is also forced out leaving behind minerals like quartz. Sedimentary rocks can be formed from either s______, clay, silt and mud. Which are the older sediments, ones found on the bottom or on the surface ? Formation of sedimentary rocks: Word bank: rocks sand Sedimentary rocks Sediments accumulating in a river delta Diagram Weathering and erosion of rocks exposed at the Earth’s surface forming small particles. Weathered rock fragments begin to settle as sediments. With time, these Notes Sediments form, collect layers accumulate. Pressure on the lower layers cause these particles to and are buried. Pressure bond together. Water is also forced out leaving behind minerals like quartz. then compacts sediments Sedimentary rocks can be formed from either sand, clay, silt and mud. into sedimentary rocks.
9. Slide 9: Science Interactive LTD Copyright 2005 Sedimentary rock formation two Sedimentary rocks can be made from clay, plant material, silt, sand and mud. Sedimentary rocks are relatively s______ when compared to metamorphic and igneous rocks. England’s land mass is largely made from relatively y________ sedimentary rock, between 20 and 400 million years old. In the table below are some examples of the starting materials and the resulting sedimentary rock types that we can find right across Europe and England. Why and how are fossil formed in layers of sedimentary rocks ? Formation of sedimentary rocks: Word bank: soft young Sedimentary rocks Coal Sandstone Limestone Diagram Weathering and erosion of rocks exposed at the Earth’s surface forming small particles. Sediments form, collect Notes Coal is formed from layers of fossilised fern and tree material. and are buried. Pressure Sandstone is formed by compacting sediments and rock particles then compacts sediments similar to sand. Chalk is formed from layers of shells and animal into sedimentary rocks. bones rich in calcium carbonate (CaCO3)
10. Slide 10: Science Interactive LTD Copyright 2005 Sedimentary rock and fossils Many animals and plants are fossilised in layers of m____ and silt during the formation of s___________ rocks. Minerals in the layers of sedimentary rocks slowly replace the bone and soft t_______ of animals leaving behind fossils which give us an insight into what extinct species looked like. Fossil evidence has helped support the many theories about evolution and how different species have evolved and changed over many millions of years. Fossils are only found in sedimentary rocks...why ? Examples of fossils found in sedimentary rocks: Word bank: mud sedimentary tissue Fossils Diagram Animals and plant remains are covered with sediments. Their bones are then replaced by minerals forming fossils.
11. Slide 11: Science Interactive LTD Copyright 2005 Metamorphic rock formation one Metamorphic rocks can be formed from both sedimentary and i________ rocks. Movement of the Earth’s crust can bury rock and rock layers deep underground. Deep underground heat, p_________ and time changes how the rock minerals are arranged. Marble used in sculptures, kitchens and bathrooms is one of the most important examples of metamorphic rock. Marble is formed from sedimentary chalk which is made from layers of calcium carbonate found in the remains of boned animals and molluscs. Metamorphic rock: Word bank: igneous pressure Metamorphic rocks Changing rocks with heat, pressure and time Diagram Shale Limestone Conglomerate Organic remains heat, pressure & time Sedimentary or igneous rocks that are buried and subjected to very high Slate Marble Gneiss Oil Oil shale temperatures and pressures. Notes Metamorphic rocks are formed deep inside the Earth’s crust. Over time the mineral structure is changed Heating by the magma contained in the mantle, causes the rock forming metamorphic rock crystal structure to be rearranged therefore changing the rock’s minerals and structures. properties. Chalk, the remains of shells forms marble.
12. Slide 12: Science Interactive LTD Copyright 2005 Metamorphic rock formation two During the formation of metamorphic rocks, the mineral structures of the rocks are changed without the rocks actually becoming m________. Metamorphic rocks show bands of crystals. Gneiss rock, for example is an good example of metamorphic rock. This rock may have been igneous granite, but heat and pressure changed it. Slate used in the building industry for roofing is formed when sedimentary mudstone is heated under pressure. The microscopic c_________ in slate line up. This is why slate can be split to form roof tiles ! Formation of metamorphic rocks: Word bank: molten crystals Metamorphic rocks Types of metamorphic rocks Diagram Notes Metamorphic rocks are sometimes highly colourful like the various Sedimentary or igneous rocks that are buried and marbles we find used for making statues, kitchen tiles and bathroom subjected to very high surfaces. Pictured above is a very small sample of metamorphic temperatures and rocks...observe their colour and structure. pressures.
13. Slide 13: Science Interactive LTD Copyright 2005 Igneous rock formation one Igneous rocks forms from molten rock called magma. These type of rocks are formed when molten magma from v__________ rise to the Earth’s surface and cools. They are mineral rich with these minerals being arranged in crystals. How quickly the lava flows cools, determines the size of the crystal found in the rock. Basalt, an example of a very common form of i__________ rock covers most of Scotland and is aged around 4 billion years. Scotland was formed from huge lava flows from super volcanoes. Explain why you cannot find fossils (plant or animal) in igneous rock layers ? Igneous rock: Word bank: volcanoes igneous Igneous rocks Cooling products of lava flows...basalt flows Diagram Meting of rocks that are buried deep, close to the Earth’s hot mantle. Notes Millions of years ago, volcanic activity spewed out huge basalt Magma rises and forms lava which then cools and flows which then cooled and formed many of the continental land crystallises over time masses we see today. Basalt is extremely hard and resistant to forming igneous rock. physical and chemical weathering.
14. Slide 14: Science Interactive LTD Copyright 2005 Igneous rock formation two Molten rock from deep underground rises to the surface through cracks in the Earth’s crust. A volcano spews out many millions of tonnes of molten l_____ or even volcanic ash. Lava then cools and forms igneous rock. Around the plate boundaries, where volcanic activity is still very high, new islands rise to the surface from the constant e________ and cooling of lava. These islands form atolls. Also, volcanic glass is responsible for some of the most stunning beaches in Japan and other volcanic islands. Formation of igneous rocks: Word bank: lava eruption Igneous rocks Types of igneous rocks Diagram Notes Igneous rock comes in many forms. Pictured above are molten lava Magma rises and forms lava which then cools and flows from volcanic activity (basalt.) Also shown are huge areas of crystallises over time land covered by volcanic ash. Just as some land is lost, new land is forming igneous rock. created from deep underneath the ocean.
15. Slide 15: Science Interactive LTD Copyright 2005 Calcite the mineral CaCO 3 Calcite is a very important mineral and is a general name for Calcium Carbonate with the formula CaCO3. Calcite comes in several forms including chalk, limestone and m__________. Chalk, limestone and marble are important, because they are all used in the building industry. Chalk is used to manufacture c________ and quick lime. Limestone and marble are both used for building materials. The cliffs at Dover contain chalk...How were these cliffs formed ? Calcite: its forms and uses: Word bank: marble cement Calcium carbonate Calcite the mineral in its various forms Diagram 2+ 2- Ca O 2+ C O O 2- Ca O Notes Calcite (CaCO3) comes in many forms. Chalk and limestone found C O O in England is rich in calcium carbonate. Marble is the most expensive form. It is ideal for use in kitchen and bathrooms. It is also an ideal material for statues, like those pictured above.
16. Slide 16: Science Interactive LTD Copyright 2005 Using Calcite CaCO quicklime 3 Calcite or Calcium Carbonate with the formula CaCO3 comes in several forms including chalk, limestone and m__________. Limestone is used in huge quantities in the building industry as a raw material for concrete production. Concrete is quicker, cheaper, stronger and easier to use for building, when compared to using s_______ or brick. It can also form any shape because it is poured and then allowed to set. What is steel reinforced concrete and why use steel rather than iron ? Limestone for concrete: Word bank: marble stone Calcium carbonate Manufacture of Calcium oxide (quicklime) Diagram 2+ Carbon dioxide 2- Ca O 2+ Calcium carbonate Calcium oxide Calcium carbonate 2- C O O Ca O Heat C O O Notes When limestone is heated strongly (CaCO3), the compound breaks up or decomposes. Carbon dioxide breaks away leaving calcium with just one oxygen. This is called calcium oxide or quick lime. This is soluble and a very strong alkaline. It reacts with water to form slaked lime or calcium hydroxide [Ca(OH)2]. Slaked lime is used for several uses including soil neutralisation and cement manufacture.
17. Slide 17: Science Interactive LTD Copyright 2005 Using Calcite CaCO Concrete 3 When Calcium Oxide is made from heating Calcium Carbonate (CaCO3), it can be used to make cement and c________. Limestone (CaCO3) is heated in a kiln forming quicklime (CaO) and then mixed with clay and sand. This process forms a grey powder called cement. When water is added and the cement is poured, a slow reaction makes the cement go hard. During this reaction, the quick lime reabsorbs carbon dioxide from the atmosphere. Cement and concrete are often h_______ than natural stone. Where would you place a cement factory...explain why ? Making concrete: Word bank: concrete harder Concrete Manufacture of cement or concrete Diagram Calcium Carbonate Clay and Sand Rotary kiln (Calcium Oxide) Heat Cement Grinder Notes Vast amounts of concrete and cement are used to build flats, houses, office building and roads. Without concrete, we would still be using red brick or natural stone.
18. Slide 18: Science Interactive LTD Copyright 2005 Using Calcite CaCO Glass 3 Glass is a useful material because it is transparent, hard and non absorbent. Glass is made from heating very pure Silicon Dioxide (sand) and Calcium Carbonate (Limestone.) The two chemicals react when heated and give off carbon dioxide. When the reacting mixture cools, it forms glass sheets which can then be used in construction. Glass is used to allow l______ into a building whilst keeping the elements out. Glass can also be coloured by adding trace amounts of metal ions. What is the synthetic replacement for glass...what are the advantages and disadvantages of using this material ? Making glass: Word bank: light Glass Manufacture of glass from sand and calcium carbonate Stained glass Diagram Calcium Carbonate Pure Sand Rotary kiln (Molten glass) Heat Molten glass (calcium silicate)
19. Slide 19: Science Interactive LTD Copyright 2005 Using Calcite CaCO Pig iron extraction 3 Calcium carbonate is also used during the s_________ of iron oxide. Impurities in the iron ore are trapped by the calcium oxide, float to the surface and are then removed. This waste product is called slag. If the impurities were left in the iron, it would reduce its overall quality. Blast furnace process: Word bank: smelting Diagram Diagram Process Diagram Formation of carbon monoxide Iron ore Diagram 2C + O2 2CO (1700oC) Notes: The carbon in coke reacts with oxygen to form carbon monoxide a powerful reducing agent. Coal Reduction of iron oxide 3CO + Fe2O3 2Fe + 3CO2 (900oC) Heat Notes: The carbon monoxide gas displaces iron from its oxide producing carbon dioxide and molten iron which is collected. Smelting Impurity Formation (Slag) CaCO3 + SiO2 CASiO3 (1200oC) Notes: Limestone reacts with silicon Cooling impurities to form slag which floats to the surface and is removed.
20. Slide 20: Science Interactive LTD Copyright 2005 Weathering rocks An essential part of the rock cycle is weathering. All rock forms can be worn away by physical, chemical and biological weathering. Over thousands of years, the slow process of weathering, reduces rocks to small fragments and sediments. These particles provide new material for forming s___________ rocks. If buried and heated, these layers can be changed or metamorphosed over time forming metamorphic rocks. Further burial and heating can lead to the formation of i_________ rock. Weathering processes: Word bank: sedimentary igneous The rock cycle Physical Chemical Biological Physical weathering: The impact of physical weathering on rocks, produced by gravity, rivers, wind and ice flows. Chemical weathering: The impact of chemicals in the atmosphere dissolved in the rain which Uplift, Erosion, Sediments, Burial, falls and reacts with minerals in the rock. Biological weathering: The Heating, Pressure, Time & Uplift impact of plant or animal life on rocks.
21. Slide 21: Science Interactive LTD Copyright 2005 Physical weathering Physical weathering is the result of changes in t____________. These changes can break rocks. Different rates of expansion and c__________ causes stresses to build up eventually cracking the rock. Onion skinning or exfoliation: In deserts, the day time temperature is very hot causing e__________ of the rock. At night, the rock contracts as it cools. This repeated warming and cooling causes exfoliation or the rock to flake off. Freeze and thaw: In small cracks, trapped water freezes. When ice is formed it expands forcing the crack apart. Repeated over many times, even large rocks can be broken apart. Physical weathering: Word bank: temperature contraction expansion The rock cycle Freeze and thaw Exfoliation Freeze and thaw: Where Onion skin or exfoliation: Heating temperatures drop below zero, by the solar rays during the day cracked rock can fill with water. and cooling at night leads to the This then freezes forming ice rapid expansion and contraction of Uplift, Erosion, Sediments, Burial, which then expands. The force the rock. The stress induced leads Heating, Pressure, Time & Uplift produced deepens the crack and to rocks breaking apart or flaking separates the rock. as pictured above.
22. Slide 22: Science Interactive LTD Copyright 2005 Chemical weathering Chemical weathering is the result of rocks interaction with acids, oxygen or water. They cause rock weathering by reacting with or dissolving many of the rock minerals. Rain water is weakly a_______ with a pH of about 5.5. Rain water contains carbonic acid, from dissolved carbon dioxide and sulphuric acid from s_________ dioxide released during the combustion of fossil fuels like petrol. Why are buildings found in large cities and near busy roads subjected to high levels of chemical weathering ? Chemical weathering: Word bank: acidic sulphur The rock cycle Carbonic acid Sulphuric acid Oxygen Carbonic acid: The weak carbonic acid attacks rocks like chalk, marble and limestone which all contain calcite (CaCO3) Sulphuric acid: Most fuels contain sulphur which when combusted forms sulphur dioxide. This then forms sulphuric acid, stronger and more damaging than carbonic acid. Oxygen: Oxygen can combine with iron Uplift, Erosion, Sediments, Burial, metal present in rocks forming rusty brown streaks of iron oxide. This Heating, Pressure, Time & Uplift can weaken the rock over time.
23. Slide 23: Science Interactive LTD Copyright 2005 Biological weathering Biological weathering is the result of the effects of plant and animal activities on all rock types. Plant and tree roots can invade bedrock and cause widespread cracking, although tree roots can help stabilise steep sided slopes and the topsoil, therefore reducing e_________ by running water or rain. Animals burrowing, for example rabbits, can also cause damage to the bedrock. Smaller animals including many insects have a widespread effect on the soil and deeper rock layers. Biological erosion: Word bank: erosion The rock cycle Plant and tree roots Animal burrowing Insect burrowing Plant roots: Plant and tree roots can cause rock weathering by invading the bedrock causing widespread cracking and destabilisation. Burrows: Animals that burrow can weaken whole areas of the bedrock by their tunnels. Insects: Even small insects Uplift, Erosion, Sediments, Burial, and animals can have a huge influence on the bedrock. Ants and Heating, Pressure, Time & Uplift termites move huge amounts of material to create their nests.
24. Slide 24: Science Interactive LTD Copyright 2005 Erosion The movement of rocks by gravity, w_____, rivers, seas and even ice flows can further breakdown rock fragments. This is called erosion. These small rock fragments are produced as a result of chemical, physical or biological weathering. During their transportation they are further eroded by: Gravity Wind Rivers Seas Ice flows Erosion and the rock cycle: Word bank: wind The rock cycle Wind Rivers Sea Strong winds carry small grains. This can wear away soft sedimentary rock. This is often seen in deserts. Rivers carry rock fragments. The size of the rock fragments depends on the rate of water flow. This erosion leads to the formation of valleys. Waves Uplift, Erosion, Sediments, Burial, can carry huge amounts of rock fragments that pound our coastline. Heating, Pressure, Time & Uplift Rock cliffs are eroded mostly below the water line.
25. Slide 25: Science Interactive LTD Copyright 2005 Extension questions and homework 1: Define the following terms: Sedimentary, Igneous, Metamorphic, Minerals, Weathering & Erosion. 2: Look at the diagram of the three types of Rock types. Complete the table. Sedimentary Igneous Metamorphic Rock Examples How are they formed What are there properties Sedimentary Igneous Metamorphic 3: Using the rock cycle, describe the steps required to turn: a) Igneous rock into sedimentary rock b) Igneous rock into metamorphic rock. c) Sediments into sedimentary rock. 4: A sample of limestone can be distinguished from a sample of sandstone by adding dilute acid. No reaction takes place with the sandstone. Describe what you would see with limestone and acid: Give a word equation for the reaction. 5: Draw a diagram to show the process of fossilisation of dead plant and animals in layers of silt and mud before the formation of sedimentary rock. Why are they not found in igneous or metamorphic rocks.
26. Slide 26: Science Interactive LTD Copyright 2005 6: Complete the table: Type of weathering Physical Chemical Biological Caused by ? _____________________ ____________________ ______________________ ___________________? ___________________? _____________________? Diagram 7: Describe how: a) Frost damage can weather rocks. b) Rapid changes in daily temperatures can weather rocks. c) Rain water becomes acidic from combusting fossil fuels. d) Valleys are formed by rivers over millions of years. e) Moving water can erode rocks over time. 8: Complete the following: As weathered pieces of rock are transported by gravity, _________ or water they can wear away more rock. This process is called ___________. Sedimentary rock is formed when ____________ in a river are deposited in lakes or ________. Igneous rock forms when _________ lava cools. Metamorphic rock is formed when either ______________ or ______________ is subjected to heat and ___________ over time. Internet: Go to google.co.uk and find about the last eruption of Mount St. Helens in the USA. Also find out about fossil formation in sedimentary rocks.