The major layers of the Earth, starting from its center, are the inner core, the outer core, the mantle, and the crust. These layers formed as the building blocks of Earth, known as planetesimals, collided and collapsed under their own gravity around 4.5 billion years ago. At that time, the heaviest elements (like iron and nickel) sank to the core, while the lighter elements (like silicon, oxygen, and carbon), rose to form the mantle and crust.
The crust itself is composed of many layers, which are the ones we can see at the surface. Most continents have a crystalline core, known as a ‘kraton’. Every continental kraton is then draped in many layers of sedimentary, igneous, and metamorphic rock. The most dramatic layers, like those in the mountain ranges above Santa Barbara, are often sedimentary rocks, which formed as long-gone mountain ranges eroded away and the resulting sediments were deposited somewhere else on the continent. A change in tectonic plate motion then caused those sedimentary layers to be brought up to where we can see them today.
When volcanoes erupt, the lava that comes out can spread across broad areas, forming a layer of igneous rock within the sedimentary layers. Thus, most of the layering on the Earth’s surface is due to erosion and deposition of mountain ranges, and lava flowing out on the surface.
Earths Formation and its Interior Structure
Earth formed about 4.6 billion years ago during the birth of our solar system. This data comes from meteorites and moon rocks. For several hundred million years after the formation of the solar system, the planets were continuously bombarded by meteoric debris thus the surface of the Earth probably remelted repeatedly by the impacts of large asteroids. This early bombardment continued until about 3.8 billion years ago.
During the next major phase of earth’s formation cooling and differentiation of the Earth’s layers occurred. Dense materials sank to the center, forming an iron-nickel rich core. Lighter buoyant silicate-rich magma rose to the surface. The remaining material between the core and the magma formed Earth’s thickest layer, called the mantle,which is composed mainly of iron, magnesium, calcium-rich silicate minerals