Rocks
vocabulary: mineral, igneous rock, sedimentary rock, metamorphic rock
Rocks are not all alike. There are about 600 kinds of rocks. Although rocks look and feel different from each other, all rocks are made of the same type of material. All rocks are made of minerals. A mineral is a substance found in nature that is not a plant or an animal. Minerals are the building blocks of rocks.
All of Earth’s rocks are formed in one of three ways. Some rocks, like granite, are formed when melted rock below the surface of Earth cools and hardens. Other rocks, like basalt and obsidian, are formed when melted rock flows out onto Earth’s surface, where it cools and hardens. Other rocks are formed when bits of soil, mud, and rock in the bottoms of rivers, lakes, and oceans pile up over time. As the layers build up they get cemented together, forming solid rock. Sometimes rocks get squeezed and heated below Earth’s surface. When this happens new rocks are formed.
Earth is an enormous ball with an outer “crust” of rock. The surface of Earth has many different shapes, such as mountains. The different shapes on Earth’s surface are landforms. A landform is a feature on the surface of Earth. The land along the edge of a body of water is a beach. Beaches are flat, narrow stretches of land. A beach is made up of sand, gravel, or pebbles. Another landform is a plain. A plain is a large area of land with few or no hills. Plains have thick layers of soil. A third landform is a valley. A valley is an area of land lying between hills or mountains. Rivers or streams often flow through valleys. A plateau is also a landform. A plateau is a flat area of land that rises above the land that surrounds it.
Soil
vocabulary: soil, humus, topsoil, subsoil
Rocks and soil are natural resources. A natural resource is a material on Earth that is necessary or useful to people. Rocks are important building materials. Crushed limestone is used in making cement. Sand is used to make glass. Weathered rocks are part of the soil. Soil is the part of the ground that plants grow in. Without soil, there would be no plants on the land. People and animals need plants for food.
Soil is a mixture of tiny rock particles, minerals, and decayed plant and animal material. Growing plant roots, worms, and insects make spaces for air and water. There are usually two layers of soil. The top layer, called topsoil, is made up of very small particles that are dark in color. Topsoil has lots of minerals and decayed plant and animal material. Topsoil holds water well, which is also necessary for plant growth. A layer of soil called subsoil lies below the topsoil. Subsoil is made of bigger particles. It does not have decayed plant or animal material. Below the subsoil is solid rock.
There are many different kinds of soil. Different soils have different types of rock and minerals in them. Some soils have more water or plant and animal material than others. The type of soil in a particular place affects what kinds of plants can grow there.
Some natural resources are renewable resources. A renewable resource is a resource that can be replaced or be used over and over again. Soil is an example of a renewable resource. The erosion of soil happens quickly when soil is unprotected. Soil is unprotected when forests are cut down or farmland is left bare. Although soil is renewable, it takes many years for soil to form. It is important to conserve soil. To conserve something means to protect it and use it wisely. Good farming practices, like contour farming and planting cover crops, help conserve the soil.
Fossils
vocabulary: fossil, fuel, cast, mold, imprint
A fossil is the imprint or remains of something that lived long ago. People have found fossils that are more than three billion years old!
After plants or animals die, their soft parts decay or are eaten. Hard parts last longer. These parts might become fossils. Bones, shells, and teeth have all been found as fossils.
Some fossils form in amber. Amber is hardened tree sap. But most fossils form in sedimentary rock. Silt, sand, and mud build up slowly and cement together to form rock. The rock may form around the remains of living things, which become fossils.
Fossils form in other ways, too. Shallow prints or marks in solid rock are called imprints. Shells often leave fossils called molds. A mold is an empty space in rock where something once was. When minerals seep into the empty space, they form a copy of the mold’s shape. This copy is called a cast.
Fossils are useful because they can teach us what life was like long ago. We know about dinosaurs only because of the fossils they left behind. Fossils also teach us how Earth’s landforms and oceans have changed. Fish fossils have been found under dry land. This tells us that this land was once under water.
What are fossil fuels? A fuel is something that is burned for energy. Fossil fuels are fuels that formed from plants and animals that lived long ago. Coal, natural gas, and gasoline and other oils are all fossil fuels.
How did coal form? Millions of years ago, swamps covered much of Earth. Layers of dead, decaying swamp plants formed a soft material called peat. Over time, layers of rock formed over the peat. Slowly, the peat changed into coal.
Resources
vocabulary: natural resource, renewable resource, nonrenewable resource, pollution
Diamonds are natural resources. Diamonds are hard to find. They are hidden below Earth’s surface. They must be mined, or dug up, before they can be used. Diamonds take many years to form. Diamonds are an example of a nonrenewable resource. A nonrenewable resource is a resource that cannot be reused or replaced in a useful amount of time.
Many of the fuels we use for energy are also nonrenewable resources. Coal, oil, and natural gas are fuels. About 200 years ago, most people burned wood for fuel. One hundred years ago, coal provided almost all the energy used in the United States. Today, oil and natural gas are the fuels used for most of our energy needs. Coal, oil, and natural gas are nonrenewable resources.
Most coal was formed millions of years ago when swamps covered large parts of Earth. Plants growing in the swamps died and sank to the bottom. Layers of decayed plants formed a soft material called peat. The peat sank deeper and deeper. Eventually the peat was buried. Thick layers of rock eventually covered the peat.
Oil and natural gas are fuels that have many uses. They are both used for heating buildings and homes. Natural gas is also used for cooking food on gas stoves. Oil is made into gasoline, which powers cars and other vehicles. Oil is a thick, brown or black substance found in rocks below Earth’s surface. Natural gas is often found in the same places. Both oil and natural gas formed from the rotting remains of tiny sea creatures that lived millions of years ago.
Water is a renewable resource. Water can be used over and over again, but it is never used up. Air, like water, is a renewable resource. Air is a mixture of gases.
G3 Earth Science Vocabulary Review – Jeopardy