Earth s Resources. Earth s Surface

Size: px

Start display at page:

Download "Earth s Resources. Earth s Surface"

Milo Brown
5 years ago
Views:

1 Earth s Resources Earth s Surface Earth s surface is made up of a layer of rock called the crust. The crust covers all of Earth. It is several miles thick. Most of the crust is under water. The upper part of Earth s crust has different features called landforms. A landform is a natural feature of Earth s surface. Plains are flat landforms on low ground. Plateaus are flat landforms on high ground. Mountains, valleys, and canyons are also landforms. Some landforms take a long time to form. It may take a million years to form a mountain. Other landforms are created quickly. A landslide can change the shape of the land fast.

2 Weathering Landforms are always changing. Rocks in Earth s crust are broken into smaller pieces in a process called weathering. There are two kinds of weathering. They are chemical weathering and physical weathering. Chemical weathering causes rocks to change to other materials and break down. For example, rainwater often has a weak acid in it. The acid mixes with rock. It forms a new chemical that can wash away. This causes the rock to break down. In physical weathering, rocks are broken into smaller pieces of the same kind of rock. Wind, water, and ice can cause physical weathering. Waves hitting the shore break down rocks by physical weathering. Erosion can carve canyons.

3 Erosion Gravity, wind, moving water, and moving ice can move pieces of weathered rock. The process of carrying away weathered bits of rock is called erosion. Rock materials that are picked up in one place are later dropped somewhere else. Moving water can carry materials across Earth s surface. Over time moving water can carve valleys or canyons. Earth s gravity is a force that pulls material downward. Glaciers are big sheets of ice. Gravity can move glaciers downhill. Glaciers wear away rock and soil as they move.

4 Minerals The salt you put on your food is a mineral. Minerals are natural nonliving solid crystals that make up rocks. There are thousands of different minerals. But most rocks are made up of only a few. These are called rock-forming minerals. Wherever one kind of mineral is found, it will have the same basic structure. For example, quartz is a mineral found in many places. A piece of quartz on a beach has the same structure as quartz on a mountain. Most rocks are made up of several minerals. But some rocks have only one or two minerals. Scientists can identify minerals by observing and testing their properties. These include color, luster, hardness, streak, cleavage, and crystal shape.

5 Color and Luster It is easy to see the color of a mineral. But the same mineral can be different colors. Pure quartz is clear. Other materials mixed with quartz can make it different colors. Scientists must look at other properties to identify a mineral. One property is luster. Luster is the way the surface of a mineral reflects light. A glassy luster is shiny. A metallic luster looks like polished metal. A greasy luster is dull. Galena is a mineral with a metallic luster. Hardness Hardness is how easily the surface of a mineral can be scratched. Talc is the softest mineral. The Mohs Scale ranks minerals by hardness. A mineral can scratch other minerals that have a lower hardness number. For example, calcite has a hardness of 3. It can scratch gypsum, which has a hardness of 2. Streak A mineral can leave a mark if it is scratched across a special kind of plate. Streak is the color of the powder that the mineral leaves behind. Some minerals have a streak that is the same color as the mineral. Other minerals have a streak that does not match the mineral s color.

6 Shape and Cleavage Each mineral has crystals that are a certain shape. The shape helps identify a mineral. For example, fluorite has cube-shaped crystals. Scientists may need a magnifier or microscope to see a crystal s shape. Most minerals will break in a certain pattern. Minerals that break along smooth, flat surfaces have cleavage. Mica breaks into thin layers that are flat and smooth. Other minerals break in different patterns. Other Properties Some minerals are attracted by magnets. The mineral magnetite in attracts objects that are made of iron. Some minerals can be cut or shaped. Some have a certain smell. Some react to acid.

7 Classifying Rocks Rocks are grouped by how they are formed. There are three main kinds of rocks. They are igneous, sedimentary, and metamorphic rocks. Igneous Rocks Some rocks form from other rocks that have melted and cooled. Rocks that form from melted rock are called igneous rocks. Some igneous rocks form from magma. Magma is melted rock below Earth s surface. Igneous rocks can also form above Earth s surface. When a volcano erupts, magma reaches the surface. Here the melted rock is called lava. When lava cools, it hardens into igneous rock. Basalt is a common igneous rock. Pumice forms from lava that has lots of trapped gas bubbles. Sedimentary Rocks Sedimentary rocks form when layers of sediments settle on top of one another and harden. Sediments are made up of soil and bits of rock. They may also contain shell or other parts of once-living things. Water, wind, ice, and gravity are forces that move sediments. Over time, sediments settle and form layers. These layers can be found on land or at the bottoms

8 of oceans, rivers, and lakes. New sediments press older layers together. Sandstone can form from quartz sand. Limestone forms from tiny bits of skeletons and shells. Metamorphic Rocks High temperatures deep inside Earth can change rocks. Rocks can also be changed by the weight of other rocks above them. Rocks that have changed as a result of heat and pressure are called metamorphic rocks. Heat and pressure can change a rock that contains graphite. Graphite is made of carbon. Heat and pressure can turn graphite into diamond. Metamorphic rocks can form from all kinds of rocks. Sedimentary or igneous rocks can become metamorphic rocks. One kind of metamorphic rock can become another kind.

9 The Rock Cycle Rocks are constantly being formed and destroyed. Old rock changes into new rock in an ongoing process called the rock cycle. Rocks can change from one kind to another. These changes can happen in any order. Not all rocks complete the entire rock cycle. Deep in Earth s crust, heat melts rock to form magma. Magma erupts onto Earth s surface. Lava forms igneous rock. Magma beneath Earth s surface hardens into igneous rock. Heat and pressure change igneous rock into metamorphic rock. Over time igneous and metamorphic rocks become layers of sediment. Layers of sediment harden into rock. Heat and pressure change sedimentary rock into metamorphic rock.

10 Natural Resources Natural resources are supplies found in nature. Plants and animals are natural resources. Water, air, minerals, and soil are nonliving natural resources. All living things depend on natural resources. Plants need air, sunlight, soil, and water to live. People need air, water, and plant and animal resources.

11 Renewable Resources Renewable resources are resources that can be replaced. Plants and animals are renewable resources. So are water and air. Water Water is one of the most important renewable resources. All living things need water. Earth s water is recycled all the time. But only a small amount of Earth s water is drinkable. It is important not to waste water. Solar and Wind Energy Solar energy and wind energy are renewable resources. They never get used up. Solar cells can change the sun s energy into electrical energy. Windmills can be used to make electricity. Some homes, schools, and businesses use solar energy to heat water or produce electricity.

12 Nonrenewable Resources Some resources cannot be replaced. Nonrenewable resources are resources that are in limited amounts. Some are used up faster than they can be replaced in nature. Recycling is saving materials or using them again instead of throwing them away. This is one way to save resources. Fossil Fuels and Ores Oil, coal, and natural gas are nonrenewable resources. They are fuels, which means they are burned to provide energy. They took millions of years to form. Ores are rocks that have valuable minerals. Iron is an example of a mineral found in ores. Iron is used to make steel.

13 Glossary erosion igneous metamorphic mineral nonrenewable resource renewable resource sedimentary weathering the process of carrying away weathered bits of rock rock that forms from melted rock rock that has changed as a result of heat and pressure a natural, nonliving solid crystal that makes up rocks a resource that exists in limited amounts or is used faster than it can be replaced in nature a resource that can be replaced rock that forms when layers of sediments settle on top of one another and harden a process by which rocks in Earth s crust are broken into smaller pieces

4 th Grade Science Unit C: Earth Sciences Chapter 6: Minerals and Rocks Lesson 1: What are minerals?

4 th Grade Science Unit C: Earth Sciences Chapter 6: Minerals and Rocks Lesson 1: What are minerals? mineral A mineral is a natural, nonliving, solid crystal that makes up rocks. All over the world, each