Continental crust

The continental crust is the layer of rock that makes up the land we live on and the shallow parts of the ocean near land, called continental shelves. It is made from three main types of rocks: igneous, metamorphic, and sedimentary. This layer is often called sial because it has more aluminium silicates. This makes it less dense than the oceanic crust below, which is called sima and has more magnesium silicates.

Most of the continental crust is dry land that is above sea level. However, a large part of one continental crust called Zealandia lies under the Pacific Ocean. Only a small part of Zealandia, mostly made up of New Zealand, reaches above the water.

Thickness and density

The continental crust has many layers. It is lighter than the material deep inside Earth called the mantle. It is also lighter than the oceanic crust, which is under the oceans. Continental crust is much thicker, ranging from 25 to 70 km, compared to oceanic crust, which is only about 7 to 10 km thick. It covers roughly 41% of Earth's surface and makes up about 70% of the total crust.

Importance

The continental crust is mostly above sea level. This allowed life on land to develop from life in the oceans. It also creates large areas of shallow water, called epeiric seas and continental shelves, where more complex animals could live long ago during the Cambrian explosion.

Origin

All continental crust comes from melted material deep inside the Earth, called basalt. This melted material changes and mixes with older crust to form new land. Scientists think new land mostly forms in areas where one part of the Earth's crust moves under another.

There wasn’t much continental crust before 3.5 billion years ago. About 20% of today’s land formed by 3.0 billion years ago. Most of the land we see today formed between 3.0 and 2.5 billion years ago. The rest formed in the last 2.5 billion years.

Forces at work

The continents we see today change shape and size over millions of years. They can break apart, crash into each other, and come back together again in a pattern called the supercontinent cycle.

Continental crust is the thick, floating layer that makes up the land and the shallow areas near coastlines. It is less dense than the ocean floor, so when the two meet, the ocean floor usually slides back down into the Earth. This is why the oldest rocks we find are on continents, not under the oceans. When continents crash into each other, the land can push up to form tall mountain ranges like the Himalayas or the Alps.

The height of mountains depends on how thick the crust is underneath. Thick crust pushes up to form mountains, while thin crust, often found where continents are pulling apart, allows the ocean to fill in. The deep, hot conditions under the crust change many rocks into metamorphic rocks, and new rocks can form when magma pushes up from below.