In order to properly understand how and why earthquakes occur, we must understand the formation of the Earth and its internal composition.
The Earth was formed about 4.5 billion years ago from a cloud of dust and gas that revolved around the Sun. Gradually, the Earth has increasingly warmed up until it turned into a sphere of incandescent rocks and melted metal. With the lapse of time, the Earth has cooled down – a phenomenon that continues to this day. As a result of the cooling process, denser materials (such as those containing iron and sulphur) were immersed inside the Earth, while lighter materials (such as those containing silicates and water) have migrated towards the surface, where they cooled forming a solid crust.
Table of contents:
The internal structure of the Earth
The plates of the Earth
The theory of continental drift and the theory of plate tectonics
The expansion of the ocean floor and recycling of oceanic crust
