Get Dirty This activity covers the following Georgia Performance Standards: SKE2 Students will describe the physical attributes of rocks and soils. a. Use senses to observe and group rocks by physical attributes such as large/small, heavy/light, smooth/ rough, dark/light, etc. b. Use senses to observe soils by physical attributes such as smell, texture, color, particle/grain size. c. Recognize earth materials soil, rocks, water, air, etc. Background Information The formation of soil happens over a very long period of time. It can take 1000 years or more. Soil is formed from the weathering of rocks and minerals. The surface rocks break down into smaller pieces through a process of weathering and is then mixed with moss and organic matter. Over time this creates a thin layer of soil. Plants help the development of the soil. How? The plants attract animals, and when the animals die, their bodies decay. Decaying matter makes the soil thick and rich. This continues until the soil is fully formed. The soil then supports many different plants. Weathering: Weathering is the process of the breaking down rocks. There are two different types of weathering. Physical weathering and chemical weathering. In physical weathering it breaks down the rocks, but what it s made of stays the same. In chemical weathering it still breaks down the rocks, but it may change what it s made of. For instance, a hard material may change to a soft material after chemical weathering. Sediments What are sediments? As ocean waves crash against rocky cliffs, bits and pieces of rock break off. The larger pieces from pebbles and boulders; the smaller bits form sand. Some of the pieces of rock are carried out to sea and settle on the ocean bottom. Others are washed up onto land to form beaches. The sand, pebbles and boulders are examples of sediments. Sediments are materials that have settled from water or air. The materials that make up sediments include pieces of rock and the remains of animals and plants. How do sediments form? Most sediments are made of rock. The breakdown of rock into sediments is called weathering. As rocks are exposed to the weather, they are slowly broken down by the action of wind and water. Rocks can break apart into small bits and pieces or be changed into new materials. The breakup of rock into pieces is called mechanical weathering. Water causes most mechanical weathering. For example, mountain streams flowing over rock gradually wear the rock away. Water trapped in cracks in a rock can freeze and cause the cracks to become larger. When the cracks get big enough, the rock eventually splits up into smaller pieces. Water can also combine with rock to change the rock into new materials. Clays used for modeling and making pottery are formed by water combining with certain kinds of rock. The changing of rock into new material is called chemical weathering. Although most weathering is caused by the action of water, the wind also wears away rock. As the wind blows, it carries sediments. If the sediments are blown up against a rocky cliff, the scouring action of the sand hitting the rock causes mechanical weathering. In dry areas such as deserts, the wind creates large amounts of sediments. Sediments are also made of plant and animal remains. When a plant dies its roots, stems, and leaves rot on the ground. The rotting plant parts break up into bits and pieces. In swamps and marshes, rotting plant remains can pile up several feet thick over hundreds of years. Along the shore, seashells and other animal remains pileup in shallow waters. In some parts of the world, where the ocean water is warm, small animals called coral form hard skeletons form salts they take out of the water. When a coral animal dies, the hard skeleton is left. Other coral animals attach themselves to the old skeletons. Over hundreds of years these tiny skeletons pile up, making a structure called a reef. The reef can be hundreds of feet thick and miles long. How do sediments move? Sediments formed by weathering are often moved hundreds of miles away from where they were formed. The carrying away of sediments is called erosion. Most sediments are moved by running water in 1
streams and rivers. Over millions of years rivers and streams are able to erode entire mountains! As the water in a stream or river flows downstream, it carries different-sized sediments. The heavier sediments-boulders, sand, and gravel-are slowly pushed along the bottom of the riverbed. It can take hundreds of years for large boulders to make their way down from the mountaintop to the river s mouth several hundred miles away. Lighter sediments, including plant remains, silt, and clay, float in the moving water. The floating sediments are suspended in the water. The mixture of water and floating sediments is called a suspension. In deep places of the river where the water slows down, the suspended sediments slowly start to sink and eventually settle to the bottom. Sediments are also moved by the wind. In deserts, the wind pushed sand around continuously to reshape sand dunes. When volcanoes erupt, thousands of tons of ash and dust are sent into the air. These sediments can be carried halfway around the world by winds in the air! Eventually, as the winds lessen, the ash and dust settle on the surface of the earth. Activities What is Soil? Smart Board Activity Materials: soil samples, flex cam, rotten log terrarium Screen 1 Begin by asking the students to define soil. Soil is one of our most useful natural resources. From the soil we get food, clothes and materials for the houses we live in. Soil comes from broken up pieces of rock and dead leaves, tree limbs, and dead bugs. Soil is a combination of both living and nonliving materials. One part of soil is broken down rock. Another is organic matter made up of decaying plants and animals. Water and air are also a part of soil. These materials help support plant life by providing them with nutrients, water, and air. Screen 2 Explain that soils are formed over a long period of time from natural materials such as rocks, minerals, animals and plants. Weather helps make soil. When the weather gets hot, rocks can get bigger. When the weather turns cold, rocks can get smaller. If this happens often enough, the rock will crack and break up into small pieces that break into even smaller pieces. When they get really small they turn into soil. Rain and ice can also get into rocks and break them apart. Soil is filled with many living creatures, like earthworms, which are responsible for keeping the soil healthy by creating tunnels in the soil that help with aeration and drainage. They also eat decaying plant materials, which pass through and fertilize the soil. Screen 3 All soil contains sand, silt and clay particles, but in differing proportions. Soil also contains water, air and organic matter (manure, leaf mold, etc). Screen 3 This screen shows different soil types from all over the world. Help the students describe each type (color, texture, etc) Screen 4 Show the soil profile page and help the students describe the different layers. Screen 6 Why is soil important? Ask the students to tell you why soil is so important. (Soil provides ecosystem services critical for life: soil acts as a water filter and a growing medium; provides habitat for billions of organisms, contributing to biodiversity; and supplies most of the antibiotics used to fight diseases. Humans use soil as a holding facility for solid waste, filter for wastewater, and foundation for our cities and towns. Finally, soil is the basis of our nation s agroecosystems which provide us with feed, fiber, food and fuel.) Flex Cam Use the flex cam to show the students a tray of soil from the forest floor. Have them describe what they see. You can also use the Flex Cam to show the Rotten Log Terraruim. 2
Soil Layers Materials: sedimentator Show the students the sedimentator before you shake it up. Help them identify the different layers. Shake the sedimentator and allow the students to watch the sediments as they settle. Soil Types Materials: soil samples, hand lens, paper to cover tables Separate the group into smaller groups and allow the students to go to the tables to examine the soil samples. Allow time for the students to examine the samples at the various stations using the hand lens. Remind the students to feel the samples. Soil Sifting Materials: trowels, soil sieve, Allow the students to use the trowels to take samples of the soil Once each child has a soil sample ask them to look at the and use words to describe its appearance. Ask students if they think the soil would be different if all of the particles were alike or if some parts were missing. How would it be different? Starting with the largest mesh sieves, sift the soil. Place what does not go through the sieve in one pile - these are the largest particles. Ask students to examine the 2 piles. How are they alike and different? Can they think of reasons why different size particles would be good for different things? Take the soil that passed through the sieve and sift it through the next smaller mesh. Keep what did not go through the sieve separate, and continue sifting through smaller mesh screens. Students will see several piles of soil separated by the size of the particles. Questions to ask about the soil : What color is it? What is its texture? Are there a lot of rocks in the soil? Is the soil moist or dry? Does it have any insects in it? Ask students to use words that describe the different piles of soil they now have. Identify the concept of particle size: sand, silt and clay. Words might include: powdery, rough, smooth, dusty, etc. Soil Critters Materials: bug boxes, field guides Explain to the group that they will be looking for animals living in the soil. Before the students start exploring set boundaries. Make sure to show them the correct way to look under and object (turn it towards them), and that it is important to place everything back they way it was found. Allow 10-15 minutes for the students to collect. Try to place a few critters in a larger container to discuss at the end of this activity. After the students have had sufficient time to collect, gather them together and have them talk about what they found. Hold up one fresh leaf and one older looking leaf. Ask the students to tell you how the two leaves look different. Find some small pieces of leaves from the forest floor and have the students compare the pieces with the other two leaves. Finally pick up some humus from the forest floor and explain to the students that the animals they found in the soil break down leaves and other debris and add nutrients back to the forest. Ask the students for examples of how soils are used. Students may answer that soils provide a home for insects and animals. Point out examples such as anthills, animal burrows, or actual worms. Students may also answer that plants use soils. Dig up one small weed to show the root system and explain that soils provide nutrients for the plants. 3
What is soil? What makes soil? SAND CLAY AIR ORGANIC MATTER WATER ANIMALS SILT 4
Soils from around the World Soil layers WHY IS SOIL SO IMPORTANT? 5