The Rock Cycle
The story of a rock is not a simple journey at all. Rocks are a bit like grass not in the way that they are green or animals eat them.
But in the way that we walk over or see them every day and don’t really realise that they are the foundations of our planet. The Rock cycle has been going on since Earth formed 4.6 billion years ago.
Does this mean the rocks we see today are the same rocks that formed our planet?
Exactly but it gets even more interesting because these rocks used to be different rocks with different minerals.
Rocks live in a cycle which takes millions of years to complete a full circle to where it began.
Here is a short introduction to the life of a rock it may sound boring but it involves Volcanoes, Magma and the movement underground that we cannot see. Before I get started on the rock cycle here are a few facts to get you started.
- Rocks can be the size of your thumbnail or the size of a mountain.
- A rock is a group of minerals that have grown together for a long time to form a solid mass.
- Rocks work in a cycle that transforms them into three different types before repeating itself in what is called the rock cycle.
- These are – Igneous, Sedimentary, Metamorphic
Before rocks go solid they are Magma
Magma is the super-hot liquid that comes from beneath the Earths surface.
It is stored in chambers before it comes out of volcanoes on land or underwater. When the magma cools and crystallizes it turns into Igneous rock.
Through time, weathering and erosion the Igneous rock break down into smaller pieces called sediment. When this sediment is pressed together at high pressures it forms Sedimentary rock.
The Sedimentary rock is then put under extreme heat and pressure which transforms it into Metamorphic rock. Under extreme heat, the Metamorphic rock melts and returns to Magma.
Then the cycle starts all over again.
Igneous means fire formed rock. It is formed from Magma which is melted rock. Igneous rocks make up around 90% of Earths upper crust, on top of this is a layer of Sedimentary and Metamorphic rocks.
There are two different types of Igneous rocks these are called- Intrusive and Extrusive. Intrusive Igneous rocks are formed when Magma cools and solidifies beneath the Earths surface. Extrusive Igneous rocks are formed when a Volcano erupts with Magma which is cooled by the air and solidified into a rock.
Sedimentary rock covers around 70% of the Earths surface. Sedimentary rock is a collection of lots of different types of rock which have been broken down into sediment and reformed under pressure and heat into new rock.
Sedimentary rocks sometimes contain fossils which are the key to our past. You can only find fossils in sedimentary rocks because they do not get hot enough to destroy them. Sedimentary rocks are formed in layers called strata the oldest layers are at the bottom and the newest at the top.
Metamorphic Rocks form a large part of the Earths crust. Metamorphic means to change in the form they are formed at extreme temperatures and pressure.
As the sedimentary rocks get deeper into the Earth they eventually meet Magma. This Magma morphs this rock into a completely different one called metamorphic.