Layers of Rocks

Did you know that there are different types of layers of rocks?

Well, there are actually three, and here we’ll take you through what these rocks are, how they are made, and much more. Enjoy!

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What is a rock?

Rocks are stones and they form naturally and are made up of heaps of different minerals.

  • The Earth’s crust is made up of rock.
  • Rocks have been used for millions of years by humans, from early weapons, tools and different types of construction materials.

What types of rocks are there?

Rocks are generally not even or made up of exact forms that can be described by scientific formulas. Scientists generally classify rocks by how they were made or formed. There are three major types of rocks, which are metamorphic, igneous, and sedimentary. Let’s get on with learning all about these rocks.

What are Metamorphic Rocks?

  • These rocks are created by extreme heat and pressure.
  • They are generally found inside the Earth’s crust where there is enough heat and pressure to form the rocks.
  • Metamorphic rocks are often made from other types of rock for example, shale, a sedimentary rock, which can be changed into a metamorphic rock such as slate or gneiss. Other examples of metamorphic rocks include marble, anthracite, soapstone, and schist.

What are Igneous Rocks?

  • Igneous rocks are formed by volcanoes.
  • When a volcano erupts, it spews out hot molten rock called magma or lava.
  • Eventually the magma cools down and hardens. This can happen either when it reaches the Earth’s surface or somewhere within the crust. This hardened magma or lava is called igneous rock.
  • Examples of igneous rocks include basalt and granite, gabbro, obsidian and pumice, marble, quartzite, schist, granulite and slate

What are Sedimentary Rocks?

  • These rocks are formed by years and years of sediment squeezing together and then they become hard.
  • In most cases, a stream or river carries lots of small pieces of rocks and minerals to a bigger body of water. These pieces settle at the bottom and over a really long time, even millions of years, and they then form into solid rock.
  • Some examples of sedimentary rocks are shale, limestone, and sandstone, mudstone, flint, greywacke and chalk

What is the order of the layers of rocks?

There is actually no specific answer to this as rocks change over time. What we do know is that the bottom layer of rocks in the oldest, and the layers of rock get younger as they pile on top of each other.

What is the Rock Cycle?

Rocks are always changing in what is called the rock cycle. It takes millions of years for rocks to change.

Take a look at this example of the rock cycle and how rocks can change from igneous to sedimentary and to metamorphic over time.

  • Melted rock or magma comes to the earth’s surface by the force of a volcano. It cools down and there you have the igneous rock.
  • Next, the weather, a river or other events will slowly break up this rock into small pieces of sediment.
  • When sediment builds up over time and hardens over years, now you have a sedimentary rock.
  • Slowly this sedimentary rock gets covered with other rocks and ends up deep in the Earth’s crust.
  • When the pressure and heat get high enough, the sedimentary rock will change into a metamorphic rock and the cycle starts all over again.

That’s really interesting stuff!

One thing to remember is that not all rocks follow this cycle. They can go in any order at all.


Layers of Rocks Facts for Kids

  • The word ‘igneous’ comes from the Latin word ‘ignis’ which means ‘of fire.’
  • Ores rocks have minerals with metals like gold and silver.
  • Sedimentary rocks form layers at the bottom of oceans and lakes.
  • Marble is a metamorphic rock formed when limestone is exposed to high heat and pressure within the Earth.
  • Layers of sedimentary rocks are called strata.

Who would have known that a rock would be so interesting? Next time you’re out in nature, try and look for the different types of rocks, even look for some of them in your home…you’ll be surprised what you find.