The core of the Earth is not known as the lithosphere (option 1), which refers to the rigid outermost layer of the Earth`s surface. The core is also not known as the mesosphere (option 2), which is the layer of Earth`s atmosphere above the stratosphere. The core is not known as the centrosphere (option 4) either, as there is no such term used in geology.

The core of the Earth is known as the barysphere (option 3). The barysphere refers specifically to the innermost part of the core, which is made up of iron and nickel. This region is the hottest and densest part of the Earth. The core is divided into two sections: the outer core and the inner core. The outer core is fluid and surrounds the solid inner core. The inner core is solid due to extreme pressure, even though it is very hot.