The rock cycle is never-ending and is constantly changing the landscape through a series of different processes. Scientists use knowledge about the formation, weathering, and erosion of rocks to study the planet's history. Additionally, fossils that are found in rocks have allowed us to learn more about how life evolved on Earth. Students will enjoy creating visual aids to help them understand the rock cycle and types of weathering!
The rock cycle is a series of processes by which rocks are recycled over millions of years. Rocks are normally separated into three main types: sedimentary, igneous, and metamorphic. Weathering and erosion are processes that break rocks into smaller pieces. These rock particles are transported by rivers and seas and deposited in new locations. Sedimentation occurs when layers of sediment build up. Over time, compaction and cementation squishes the layers and sticks them together, which creates sedimentary rock. As these layers move underground, heat and pressure changes the rock, creating metamorphic rock. If this rock gets heated further and melts, it becomes magma, above ground, it becomes igneous rock. The rocks that are made are then weathered and eroded to start the process again.
|TYPE OF ROCK||DESCRIPTION||EXAMPLES|
|Sedimentary||Sedimentary rocks are formed over millions of years, when smaller pieces of other rocks are transported elsewhere by rivers. Over time, this rock builds up in layers, a process known as sedimentation. As more and more layers build up, the lower layers are compressed together, which is known as compaction. Water gets squeezed out from between the particles. The particles form a sort of cement that glues the particles together. This is known as cementation. Fossils are mostly found in sedimentary rock.||limestone, sandstone, chalk, shale|
|Igneous||Igneous rocks are formed due to the heat inside of the Earth. This heat can be hot enough to melt rocks. These molten rocks, known as magma, cool down and solidify, creating igneous rocks. The size of the crystals that appear in the rocks depend on the time it took the rocks to cool. If the rocks cool quickly, small crystals will form. If the rock cools slowly, large crystals will form. Igneous rocks can be further separated into intrusive and extrusive rocks. Intrusive rocks form underground, and extrusive rocks form above ground after volcanic eruptions.||obsidian, basalt, granite, gabbro|
|Metamorphic||Metamorphic rocks are changed due to pressure and heat over long periods of time. This heat and pressure that exists deep inside the Earth changes the chemical composition. It is important to note that these rocks don’t melt; rocks that melt form igneous rocks.||slate, marble, phyllite, quartzite|
Weathering is the breaking down of larger rocks into smaller pieces. There are different ways in which this can happen. These methods can be put into three categories: biological, chemical, and physical. Biological weathering occurs due to plants, animals, and other living things. Trees often have huge root systems and over time, these roots can break and split up rocks. When chemicals weather rocks, this is known as chemical weathering. Acid rain is formed when pollutants in the air are dissolved in water, causing the pH of the water to reduce. Acid rain can react with some rocks, such as limestone. Physical weathering is caused by physical changes, like temperature changes, freeze-thaw, waves, rain, and wind.
Erosion is the process by which rocks and rock particles are moved. There are four agents of erosion: water, ice, wind, and gravity. Water can move rock fragments through rivers, streams, and oceans. Ice can move these particles using glaciers. Glaciers are huge masses of ice that very slowly move over the land. Glaciers are sometimes called “ice rivers.” Wind can carry sand and dust over large distances. Sand from the Sahara Desert can be carried across the Atlantic Ocean, sometimes as far away as Florida. Gravity causes rock particles to fall away from where they are weathered. An example of this can be rock piles found at the bottom of a cliff. When these rock particles stop moving or are dropped, it is called deposition.