The Rock Cycle (science Matters)

Studying Rocks Types of Rock 6 Earth Rocks 8 Rocks and Minerals 10 The Rock Cycle 12 Gemstones 14 Rock Uses 16 Fossils in Rocks 18 Surfing Our Earth 20 Science in Action 21 What Have You Learned? 22 Words to Know/Index 24 Studying Rocks Rocks are everywhere. They lie by the sides of roads and in backyards. They form Earth's crust. Rocks are found at the bottoms of rivers and lakes. They are also found on mountain peaks. Sand, dust, boulders, and mountains are all rocks. The study of Earth's structure is called geology. Geologists are scientists who study rocks, mountains, and cliffs to learn what Earth is made from. They also learn how Earth has changed over time. • Canyons are formed by rivers cutting through rock. Layers of rock can be seen in the canyon walls. Rock Facts Although rocks are not alive, th^y are changing alii the time. Rea| on tb^ learn itiéreInteresting facts about rocks. • The oldest known rock was found in Canada. It is nearly 4 billion years old. • Rocks are made of two or more minerals. • There are hundreds of rock types. Only 20 common types of rocks are found on Earth's surface. • Up to 100,000 tons (90,718 tonnes) of rock fall to Earth from space each year. • Sometimes lightning strikes sand on a beach.The heat melts the tiny rocks that make up the sand to form a glassy rock called fulgurite. Types of Rock Geologists group rocks into three main types. These groups are based on how rocks form. Igneous rocks are made when lava cools. Sedimentary rocks are formed when layers of sediment become stuck together. Heat and pressure cause sedimentary and igneous rocks to change. A new type of rock, called metamorphic rock, forms. • Sedimentary rock is fragile. It is easily broken down by wind and rain. i I I I ..ocks can be called by many names.The word used often tells the size of the rock. Here are some rock words. Can you think of any others? PEBBLE: a small rock, usually rounded, that can be held with twofinqers STONE: a medium-sized rock that can be held in two hands a large rock tha is taller than a person BOULDER: RIVER ROCK: round rocks found along the edges and at the bottom of fast-flowing rivers a giant piece of rock that is attached to Earth's crust and does not rnoVe MOUNTAIN: Earth Rocks The planet Earth is one big rock. Earth's core is made of molten, or melted, rock. The crust is made of rocks and minerals. Ice, water, soil, and sand cover much of the crust. Rocks on Earth can be changed in two ways. Weathering is the breaking down of rocks on Earth's surface by natural forces such as frost, rain, and heat. Erosion is the removal of rock and pieces of soil by natural forces such as running water, ice, waves, and wind. These processes are part of the rock cycle. • Earth's solid crust is rock. Beneath the surface is molten, or melted, rock called magma. e I I I I I I I I I I I I I The Moon is a big rock, too. Like Earth, it is made up of smaller rocks. Scientists have brought rocks from the Moon to Earth for study. Scientists have found that rocks from the Moon are made of the same materials as some rocks on Earth. The Moon's surface is mostly made of basalt. Basalt is the most common type of rock on Earth's surface. Most of the ocean floor is also basalt. Moon basalt is darker in color and more dense t