Chapter 3 Section 4 How are sedimentary rocks formed? Objective: Describe two ways that sedimentary rocks are formed

Key Term sediment: rock particles carried and deposited by water, wind, or ice.

Sediments What happens when you mix soil and sand in a jar of water? The particles of soil turn to mud and, together with the sand, settle to the bottom of the jar in layers. The sand settle first because it is heavier than the mud. The mud settles on top of the the sand and sediments. Sediments are rock particles that are carried and deposited by wind, water, or ice.

RESTATE: What are sediments?

Natural Cement Many sedimentary rocks form in much the same way as concrete. Concrete is made up of sand, gravel, and cement. Have you ever seen trucks pouring concrete for a building? Inside the trucks, sand, gravel, cement, and water are mixed. A chemical reaction then occurs that causes the sand, gravel, and cement to bind together into concrete. As the water evaporates the concrete hardens.

Natural Cement How do sedimentary rocks form? Most sedimentary rocks are formed in water. These rocks form from sediments that settle to the bottom of lakes, rivers, or oceans. Over millions of years, the sediments pile up in layers. Some sedimentary rock forms from sediments deposited by wind or glaciers.

Natural Cement The layers of sediment may be hundreds of meters thick. As more sediment is added to the layers, the lower layers of sediment become tightly packed under the pressure and weight of the new layers. The older sediments become solid rock when water and air are squeezed out from between the sediment layers. The sediments may also become solid rock when dissolved minerals in the water cement the sediments together.

2. DESCRIBE: When does sediment become solid rock?

Sedimentary Rock From Living Things Some types of sedimentary rocks form from the remains of living things. For example, the shells or skeletons of sea animals contain the compound calcium carbonate. When the organisms die, their remains are left on the bottom of the ocean. Over millions of years, the shells and skeletons build up on the ocean floor. Some of the calcium carbonate dissolves and comes out of solution to cement the minerals together. This forms solid rock.

Sedimentary Rock From Living Things Coquina limestone is a sedimentary rock formed from shells. Chalk limestone also forms from shells. However, you cannot see the shells in it because they were formed from microscopic organisms.

3. IDENTIFY: How can shells of marine animals form sedimentary rock?

Classwork CHECKING CONCEPTS Why does sand settle to the bottom of a jar faster than mud does? What is sediment? What sedimentary rock is made up of pieces of shells? What are two types of sedimentary rock?

Classwork THINKING CRITICALLY 5. IDENTIFY: What materials combine together to bind sedimentary rock? 6. EXPLAIN: Why does sedimentary rock form in layers? 7. EXPLAIN: Why must water evaporate or be pressed out for sedimentary rock to form? 8. COMPARE/CONTRAST: How are the rocks chalk and coquina alike and how are they different? 9. EXPLAIN: How does weight affect the way in which sediments form layers?