Like an onion, the Earth has several layers. The outermost layer, the Earth’s crust, has an average depth of about 40 km. As compared with the diameter of the Earth, which is around 12,700 km, the Earth’s crust is very small. It is primarily made up of solid rocks. Below the crust is the mantle, reaching to a depth of about 2900 km. Due to the heat inside the Earth, the mantle consists of solid and molten rocks. Below the mantle is the core, made up of iron and nickel. The deeper one travels inside the Earth, the hotter it is. The temperature in the core is between 4000 and 5000 degree Celcius.
It has been known for more than 2000 years that the Earth is round, but we were able to actually see this much later only when we flew into space. The knowledge why we do not fall off from the Earth is much more recent. A journey as described by author Jules Verne in his book Journey to the Center of the Earth was, after all, impossible. Only one thing was known: the Earth is made up of soil, rocks, and water. Today, we know that the Earth is also surrounded by an air cover called the atmosphere.