The tests used to determine whether brain stem death has occurred are outlined below: 1  A torch is shone into both eyes to see if they react to the light. 2  The cornea (transparent outer layer of the eye), which is usually very sensitive, is stroked with a tissue or piece of cotton wool to see if the eye reacts.
The inner core extends another 900 miles inward towards the center of the Earth. It is believed that this inner core is a solid ball of mostly iron, and nickel. The mantle is made of much denser, thicker material, because of this the plates float on it like oil floats on water.
The Earth is made of three layers that are just like an onion â the crust, the mantle and the core. Some of these layers have even more layers in them and are always moving. The Earth is mostly made of rock and metal. As scientists can't really get right to the middle of the earth, it's not easy for them to know what's way down in the middle.