Earth Under The Microscope

Transcription

1 Earth Under The Microscope

2 Equipment list stereo microscopes Small box of rocks Large bucket containing sandstone, granite, quartz and pumice and smaller buckets Large box containing crystal display box, rocks and mineral book 2 sets of 3 syringes with soil samples (sand, loam, clay) and samples of same soil in petri dishes Small box containing demonstration materials, hardness scale items, and mystery minerals Objectives (for students) Learn about the 3 types of rock, how they are formed and some examples Learn about different properties of rocks (crystals, etc) and soils Learn what porosity (rocks) and permeability (soil) Use an identification key to identify rocks based on their properties Examine features of rocks under a microscope Use analytical skills to create hardness scale Safety notes Electrical extension cords and powerboards are used in this workshop Students should be careful not to trip on any exposed cords Students should not touch the powerboards Water-based activities to be kept separate from activities using electrical equipment Water spills to be reported to presenter who will clean up immediately Weak acid is used in the mystery minerals activity this is not to be handled by students Workshop activities In this workshop students there are 4 main activities. Activities are as follows: 1. Touchy feely table. Students use stereo microscopes to look at samples from the rocks box to see their features 2. Soil types. Students identify different types of soils, test soil samples for permeability, and infer erosive properties of soil types. 3. Rock types. Students test rocks in water to see if they are porous and create own hardness scale using samples of rocks and everyday materials. 4. Mystery minerals. Students carry out some tests on 4 unknown types of rock, record the results, then use an identification key to identify the rocks 2

3 Rundown and setup of workshop The introduction takes minutes depending on how much the kids already know (see script on page 5). Ask the teacher to form the students into 8 groups (3-4 per group). Two groups will be allocated to each activity. Allow the students to work for about 30 minutes. It will take around 5 minutes to go through the worksheet. Time Activities 0-10 Introduction. Explanation of activities. Hand out worksheets whilst the teacher organises groups Round Round Round Round Go through the worksheet and wind-up session An example of setup for this workshop is illustrated below. The best setup will change depending on the location of the power points in the room, how many tables you re given, and how big they are. Make sure you leave space for the class to come in that is clear from power cords, and also that you leave a space for the class to sit. Do your best to keep all power cords and power boards out of the way of the students. Some photos of set up are on the following page. Hardness Scale Porosity table Soil permeability (2-4 micros) Students seated in this area for presentation Mystery minerals (use as presenters table) Touchy feely table/s (8 microscopes) 3

4 Touchy feely table Photos required for soil permability Comment [MB1]: If you get a chance, can you take a photo on your mobile of this activity table set up and text to me. I will then insert into doc. Mystery minerals Porosity table (photo also required for hardness scale) Comment [MB2]: Ditto above re photo 4

5 Script QUT Extreme Science Introduction takes around 10 minutes. Dialogue is in italics. Hi, my name is.. and I am from the QUT Science & Engineering Faculty. Today we are going to investigate rocks and soils and the impacts of weathering and erosion. (First part To begin who knows the 3 different types of rocks? Igneous, sedimentary and metamorphic. Now for the tricky bit! Who knows how an igneous rock is formed? That s right, igneous rocks are formed from lava which has spewed out of volcanoes. What is lava? Lava is molten or really hot liquid rock. Lava is at least 800 degrees Celsius! When the lava cools it turns back to solid rock. The faster the lava cools the smaller the mineral crystals will be in the rock. Who has grown crystals before? You would know that the longer you leave the crystals the bigger they get. The longer time the lava takes to cool the more time there is for the crystals in the rock to grow, and so you end up with bigger crystals. Does anyone know an example of an igneous rock that comes from cooled lava? Hold up the obsidian and the basalt. These 2 rocks are both from lava. This one is called obsidian or volcanic glass, and this one which isn t so pretty is basalt. The obsidian has cooled faster than the basalt so you can t see any crystals, but the basalt has cooled a bit more slowly so it has little, tiny crystals. Obsidian is a semiprecious gem and it was used a lot by native American Indians to make axe and spear heads. The basalt is crushed up and used as road base. Does anyone know what this igneous rock is called? Throw the pumice out into the group. You might have a piece of this in your shower for removing dead skin. This is a light rock that floats on water because it is made of lots of air and only a little bit of rock. It is called pumice. Think of a volcano like a can of softdrink. If you shake the can and open the ring what happens? You hear a hiss. What is this hiss? This hiss is gas. When a volcano erupts the first stuff to come out is gas. This gas often contains heaps of sulphur so it smells really bad. The next stuff to come out of the volcano is the pumice, lots of gas with a tiny bit of rock. Lastly all of the gas is gone and straight molten rock comes out which cools to form rocks like obsidian and basalt. Does anyone know where else you can find molten rock and what it is called? Molten rock can also be found under the ground and is called magma. Magma takes a very long time to cool, so rocks formed from magma have large visible crystals. Does anyone know a rock that comes from cooled magma? Hold up the granite as a prompt as many kids recognise granite on sight. Granite is the most common igneous rock formed from magma. Granite is used to make benchtops and feature walls. McDonalds restaurants use granite for their counters and tabletops. Comment [MB3]: The first part of the presentation is taken from the old QUT Rocks presentation. I have added some info relevant to weathering and erosion at the end of this section. Next we come to sedimentary rock. Does anyone know how it is formed? Sedimentary rocks are recycled rocks as they are made out of bits of sediment which can be rocks or sand or coral or mud that have been squished together to make new rocks. Often sedimentary rocks are formed by layers of sediment which are squashed together like this one. Hold up the mudstone with fishbone fossil. See the layers on the side. A layer of brownish mud then a layer of yellow mud and another layer of brown mud and so on. Fossils are found in sedimentary rock. See the fish backbone fossil found in this rock? Hold up the sandstone. Does anyone know what this rock is called? Sandstone. What is it made of? Lots of bits of sand held together with a 5

6 mineral glue. Hold up the kaolin clay. This clay is another example of a sedimentary rock. What is clay made from? Clay is made from fine dirt or mud. Hold up the limestone. This limestone is another example of a sedimentary rock. Does anyone know what limestone is made from? Limestone is made from crushed up coral. Lastly we come to the metamorphic rocks. Who knows what the term metamorphic means? That s right, metamorphic means to change. Who knows how these rocks are made? Metamorphic rocks are made by heat and pressure being applied to rocks over a very long period of time. This heat and pressure changes the rocks, hence the term metamorphic. Let s look at a few examples. Hold up the limestone. Who can remember what this is? Yep it s limestone. Heat and pressure changes this limestone into this. Hold up the marble. Does anyone know what this is? Yep this is marble. You may have a cutting board at home made from marble. Let s look at another example. Hold up the kaolin clay. Remember what this is? Yep this is kaolin clay. Heat and pressure change this kaolin clay into this. Hold up the muscovite. This is called muscovite. It is an example of a group of rocks called mica which means many layers. Can you see why it has this name? This muscovite is crushed up and used as the sparkle in sparkle toothpaste! Today we will also be looking at weathering and erosion. Weathering is the process by which rocks, soils and minerals are broken down by physical, chemical and biological processes. Physical (or mechanical) weathering takes place when water, win and ice wear away rock fragments. Chemical weathering is when water reacts with the minerals in rocks. Biological weathering occurs when plant roots break up rocks or when animals burrow in the ground. Each of these different types of rocks we have just looked at have different weathering rates. Can you guess which types of rocks will weather faster? Harder rocks will take longer to weather than softer rocks. Usually sedimentary rocks tend to be softer than igneous rocks, which in turn tend to be softer than metamorphic rocks. Erosion is the transportation of this weathered material by water, wind ice and even gravity. When rocks weather, the small particles form the basis of soil. The parent rock will determine the type of soil. Organic matter from dead and living plants and animals give the soil provide the soil with nutrients to enable plants to grow. Today we will be investigating some properties of soils. Soils particles are classified as clay, silt or sand, with clay particles smallest in size and sand being the largest. Soils can be a combination of each of these particles. A loam soil is a combination of all three soil types. The Okay, now it is your turn. Today you have 4 activities. I will hand out the sheets and then go through the activities before you begin. Hand the sheets around. Can you see that your sheet is divided into 4 sections? Each activity is on a different table. The activities have instruction cards which you need to read carefully and follow exactly! A couple of important things to note are: The touchy feely table has heaps of rock samples for you to look at. Choose your favourite and then look for the number written on the rock. Then using the orange sheets, you will be able to answer the questions on your sheet about this rock. To use these microscopes at the touchy feely table place your specimen on the plastic dish so 6

7 you don t scratch the microscope. Look through the eyepieces which are adjustable and use the black knob on the side to focus. For the mystery mineral table you are asked to perform an acid test. You need to come and get me to do this with you (you need to keep the acid on your person at all times). Use the nails to scratch the rock, but make sure you return them to the dish when you re finished testing. Please return the magnets too. On the porosity table you will be investigating if the rocks are porous. What does this mean? It means whether or not they have holes and allow water to pass through them. Put the 4 types of rocks into the buckets of water what will you look for? To see if they sink or float, and to see if bubbles rise from the rocks. At this table, you will also be investigating the hardness of rock and create your own version of Moh s Hardness Scale to rank the hardness of rocks using a variety of everyday materials. You will need to test the hardness of items on the table by scratching against other items on the table. If an item can scratch another item from the table, which means it is harder. After testing each item against the others, you should be able to put them in order from softest to hardest. Lastly, you will be testing different types of soils for permeability the capability of water to flow through soil. You will be testing sand, clay and loam soils by pouring water into the syringes containing each soil type, then checking how much water is left on top of the soil and how much has passed through the soil in a 5 minute period. You will also get to look through the microscopes at each of the soil samples to see the difference between soil particle sizes. Now form into groups of 3-4 (depending on class size). Two groups will be allocated to each table. I will let you know when to move onto the next activity. You will have minutes to work through all the activities, then we will come back togther as a class to run though the worksheet. Comment [MB4]: We have talc listed on the activity card. It is actually kaolin so is harder than chalk. I will change by hand on the laminated worksheet if I get a chance today. Comment [MB5]: Luisa has run this new workshop a couple of times and feels the students have problems with this activity, especially making the connection to erosion rates. I d appreciate your feedback on this as well as any suggestions for alternative activities. Wrap up: Run through the porosity and soil permeability tables, Hardness Scale and associated questions. Run through identification key and the names of the 4 mystery minerals Ensure that you ask teacher to have all the children wash their hands on the way back to class. Background information - Erosion properties of rocks and soils At the soil permeability and rock hardness/porosity tables, students are encouraged to investigate some factors impacting on rates of weathering and erosion of rocks and soil. It should be noted that weathering is the first of two processes that break down the surface of the land (rocks, soils and their minerals) through mechanical (rain, wind, ice, temperature) and chemical means. Erosion, the transportation of weathered materials, is caused by the flow of water, air and ice. Gravity also contributes through surface creep, slumping and landslides, so slope plays an important role - the steeper and longer the slope the greater the rate of erosion). Vegetation cover, or lack thereof, can impact on rate of erosion - roads are especially likely to cause increased rates of erosion because, in addition to removing 7

8 ground cover, they can significantly change drainage patterns, especially if an embankment has been made to support the road. Soil erosion Physical characteristics of soil have a bearing on erodibility. Soil properties influencing erodibility include texture, structure and cohesion. Texture refers to the size or combination of sizes of the individual soil particles. Three broad size classifications, ranging from small to large, are clay, silt, and sand. Soil with a large amount of silt-sized particles is most susceptible to erosion from both wind and water. Soil with clay or sand-sized particles is less prone to erosion. Structure refers to the degree to which soil particles are clumped together, forming larger clumps and pore spaces. Structure influences both the ability of the soil to absorb water (permeability) and its physical resistance to erosion. Higher permeability (found in sandy soils) means that less water will stay on the soil surface, reducing surface erosion. However, intrasoil erosion can occur. Low permeability means that more water will stay on the soil surface. Soils with low permeability tend to not be very susceptible to surface erosion due to their high clay content. It should also be noted that human use of the land for agricultural or other purposes can loosen the topsoil, leaving it vulnerable to erosion. The last property to consider is cohesion. Cohesion refers to the binding force between soil particles and influences the structure. When moist, the individual soil particles in a cohesive soil cling together to form a doughy consistency. Clay soils are very cohesive, while sand soils are not. In the soil permeability activity, students investigate elements of Students will pour water through 3 different soils set up in syringes clay (smallest particle size), silt, and sand (largest particle size). They will rank the substances on how permeable they are compared to the others, and discuss on their worksheet what effects they think the permeability differences could have on erosion. Ref: Van Buren County, Land Information Access Association, Factors Influencing Erosion, accessed 4 July 2012 Rock/mineral erosion The weathering of rocks depends strongly on their hardness. Minerals such as quartz (a 7 on the Moh s hardness scale) will only erode if chemical weathering is involved. The Moh s hardness scale is based on 10 standard minerals. It does not have units and is not a linear scale, but a relative scale: 1. Talc 2. Gypsum (Plaster of Paris) 3. Calcite 4. Fluorite 5. Apatite 6. Feldspar 7. Quartz 8. Topaz 8

9 9. Corundum (sapphire, ruby) 10. Diamond All minerals are covered by this scale, as talc is the softest mineral, and diamond the hardest. The hardness of each mineral relative to the others is evaluated with a simple scratch test. For comparison, this is a table of Moh s hardness for common materials: Material HM Material HM Material HM Fingernail 2.5 Copper Penny 3 Chalk 3 Tooth Dentin 3 ~ 4 Tooth Enamel 5 Amalgam 4 ~ 5 Gold 2.5 ~ 3 Knife Blade 5.5 Glass 5.5 Pumice 6 Steel File 6.5 Floor Tile 6.5 Tungsten Carbide 9 Silicon Carbide 9 ~ 10 Boron Carbide 9 ~ 10 Reference: Minerals on the Moh s scale are nearly always rounded to the nearest 0.5, so 2 minerals which have the same Moh s hardness may in fact be slightly different. Within rock groups, there is variation on the hardness scale. However, due to their composition, sedimentary rocks tend to be softer than igneous rocks, which in turn tend to be softer than metamorphic rocks. There are exceptions, such as certain types of sandstone (sedimentary) being harder than anthracite coal (metamorphic). These tendencies mean that we can say that in general sedimentary rocks erode more easily than igneous or metamorphic rocks, and that in general metamorphic rocks are hardest to erode. For this activity, students are asked to develop their own hardness scale with scratch tests. There are several different mineral samples and samples of other common items for them to rank from least hard to hardest. They will be asked to consider what effect hardness might have on the erosion of rocks. 9