Craton

Some parts of the Earth are very old.

They stay very still and strong. These parts are called cratons. They do not change much over time.

Cratons have a very thick bottom. This bottom reaches deep into the Earth. It acts like a strong root. This root keeps the land stable.

Some cratons show hard rocks on top. These are called shields. Other parts have soft rocks on top. These are called platforms.

Cratons hold the oldest rocks on Earth. Some rocks are billions of years old. They are even older than diamonds!

These strong lands are the cores of continents. They help our world stay steady.

Do you like big, old rocks?

Some parts of the Earth stay very still for a long time. These parts are called cratons. A craton is a strong, stable part of the Earth's crust. They are often found in the middle of tectonic plates.

Cratons have two main parts. Some show hard rocks at the surface. These are called shields. Other parts are hidden under soft rocks. We call these parts platforms. Cratons also have deep roots. These roots reach hundreds of kilometers into the mantle. The mantle is the layer under the crust. These deep roots help keep the land stable.

Cratons hold the oldest rocks on our planet. Many formed billions of years ago. Most were made during the Archaean eon. This was a very long time ago. Some cratons have diamonds in their roots. These diamonds are often over 3 billion years old. Cratons like the Amazonian Craton in South America are very big. They stay steady even when continents move or join together.

A craton is a very old and stable part of the Earth's outer shell. This shell is called the lithosphere, which includes the crust and the top part of the mantle. While much of our planet is always moving, cratons stay steady for a long time. They are often found in the middle of tectonic plates.

These areas are different from the parts of the Earth that are active or unstable. Cratons act like the strong, solid cores of our continents. They have survived many times when continents joined together or broke apart.

Cratons are made of two main layers. The first part is the basement, which is made of very old, hard rocks. If these rocks are visible at the surface, we call that area a shield. The second part is the platform, which is a layer of younger rocks sitting on top.

Cratons also have deep roots that reach hundreds of kilometers down into the mantle. These roots help the craton stay afloat. They have a low density, which means they are light for their size. This lightness stops them from sinking deep into the hot mantle.

Scientists have been studying these structures for a long time. The word "craton" comes from a term used by a geologist named Hans Stille. He shortened a word first suggested by Leopold Kober in 1921. Kober used the word to describe stable platforms.

In 1978, a scientist named Thomas H. Jordan shared a new idea about how they form. He suggested that much of the mantle melted to create them. This process left behind a strong, solid residue that stays stable for billions of years.

Cratons hold the oldest rocks on our planet. Most formed during the Archaean eon, between 4 and 2.5 billion years ago. They also formed during the Proterozoic eon.

You can find many famous cratons around the world. There is the Amazonian Craton in South America and the Kaapvaal Craton in South Africa. Other examples include the North American Craton and the Superior Craton in Canada. Some of these areas even contain diamonds that are over 3 billion years old.

Understanding cratons helps us see how the Earth has changed. They are like the ancient foundation of a house that stays still while everything else moves.

Even as wind and water wear them down, they keep their shape. This slow wearing down is called the cratonic regime. It can create very flat surfaces called peneplains. By looking at these stable rocks, we can learn about the very beginning of our world.

A craton is an ancient and stable part of the Earth's continental lithosphere. The lithosphere consists of the crust and the uppermost part of the mantle. While many parts of the Earth's surface are constantly shifting, cratons remain remarkably steady. They often sit in the middle of tectonic plates. This stability allows them to survive many cycles of continents merging or breaking apart. Scientists use the term craton to distinguish these stable regions from more active, unstable areas.

Cratons are built from two distinct layers. The first is the cratonic basement. This layer consists of metamorphosed crystalline and metamorphic rocks. When this basement rock is visible at the surface, the area is called a shield. The second layer is the platform. A platform is a layer of younger, weakly deformed sedimentary rock that sits on top of the basement.

Together, these layers form a massive, coherent domain of the continental crust.

One of the most important features of a craton is its deep lithospheric root. These roots extend several hundred kilometers down into the Earth's mantle. Cratons have a much thicker lithosphere than the oceanic lithosphere found under the oceans. For example, cratonic lithosphere can be up to 4 billion years old. In contrast, oceanic lithosphere is often only 180 million years old. These deep roots are unusually cold and have a low density. This low density prevents the craton from sinking into the deep, hot mantle.

The history of the word "craton" began in 1921. An Austrian geologist named Leopold Kober first proposed a similar term for stable platforms. Later, a geologist named Hans Stille shortened the term to "craton." Modern understanding of how these structures form changed significantly in 1978. That year, Thomas H. Jordan published a paper in the journal Nature. He proposed that cratons formed through a process called cratonization. This process involves the melting of the upper mantle to create stable continental cores.

Cratonization likely began during the Archaean eon, between 4 and 2.5 billion years ago. Most cratons were formed during this time. Some also formed during the Proterozoic eon, which lasted until 538.8 million years ago. Evidence for this ancient age comes from diamonds found in craton roots. These diamonds are often over 2 billion or even 3 billion years old. Currently, Archaean rock makes up about 7% of the world's cratons. However, all continents on Earth contain some crust from the Archaean eon.

Scientists have several theories about how these deep roots actually form. Jordan suggested that high temperatures in the Archaean caused massive melting. About 30 to 40 percent of the source rock turned into magma. This left behind a solid residue called peridotite. This residue was enriched in lightweight magnesium, making it less dense than the surrounding mantle. Other theories include the repeated continental collision model. This model suggests that colliding continents "knead" the crust to create deep roots.

There is also a molten plume model and an impact origin model involving large asteroids.

There are many famous examples of cratons across the globe. In South America, there is the Amazonian Craton. In Africa, you can find the Kaapvaal Craton. Other major examples include the North American Craton, also known as Laurentia. In India, there is the Dharwar Craton. Canada is home to the Superior Craton. Australia has the Gawler Craton. These massive structures serve as the ancient cores of our modern continents.

Because cratons are so old, they undergo a long process of erosion. This is sometimes called the "cratonic regime." Over vast amounts of time, wind and water wear the surfaces down. This can create very flat surfaces known as peneplains. Some cratons, like the Yilgarn Craton in Australia, were already very flat long ago. Studying these stable rocks helps geologists understand the deep composition of our planet. By looking at rock fragments called xenoliths, they can see what the deep mantle looks like.