What is Earth's crust?

The ground is the bark of its upper layer, 5 km (3 mi) to 10 km (6 miles) for oceanic bark and 30 km (20 miles) to 50 km (30 miles) for continental bark. This is less than 1% of the whole depth of the country. The bark is differentiated on the ocean part, composed of denser rocks such as basalt, diabase and gabbro, and continental cortex, composed of lighter rocks such as granite. The Earth began as a molten ball of rock, but within 100–150 million years the surface cooled and hardened. The heavier elements such as iron and nickel usually sank to the earth's core and lighter elements on top. Today, the oldest known rocks are Zircon from the Canadian shield dated 4.4 billion years ago. The current crust has many ages, from more than 3 billion years to less than one hundred million years for ocean crusts.

The continental and oceanic bark are composed of tectonic plates that float on the upper part of the molten layer below, the cloak. DepartmentRY and cloaks are a border called Mohorovic discontinuity, defined as a change in plasticity of rocks and seismic speed. Much of what we know about the internal structure of the Earth has learned by measuring the speed of seismic waves passing through it.

The ocean bark, which is thicker than the continental bark, is constantly damped - attracted under other tectonic plates - and pushes into the cloak where it melts. A large valley of the valley where the plates move apart, while the mountains form where it collides. In these rift valleys, the magma under the surface is released to replace the bark lost due to subduction. The whole ocean crust is recycled every few hundred million years.

Life on Earth is primarily responsible for contemporary chemical make -up of the Earth's crust. Since oxygen is a by -product of photosynthesis and photosynthetic organisms have developed more than 2 billion years ago, a large amount of oxygen has been released in the history of the Earth and more than 99% of the bark consists of different oxides. Some of the exitMky are chlorine, sulfur and fluorine. Silicon oxide (SiO _{2 ) is the most abundant oxide, which accounts for about 60% of the bark, followed by aluminum oxide (al 2 3 ), which accounts for 15%, calcium oxide, lime oxide, iron oxide oxide and several others.}