The innermost layer of the Earth is the Inner Core. Let's explore this in more detail:

1. Layers of the Earth:
The Earth is composed of several layers. From the outermost to the innermost, these layers are the crust, mantle, outer core, and inner core. Each layer has its own unique characteristics and composition.

2. Crust and Mantle:
The crust is the outermost layer of the Earth, and it is relatively thin compared to the other layers. It is made up of solid rocks and soil and varies in thickness from around 5 to 70 kilometers. Beneath the crust lies the mantle, which is a thick layer of hot, semi-solid rock. The mantle extends to a depth of about 2,900 kilometers.

3. Outer Core:
Deeper beneath the mantle, we find the outer core. The outer core is a layer of liquid iron and nickel that surrounds the inner core. It is about 2,300 kilometers thick. The outer core plays an important role in generating Earth's magnetic field.

4. Inner Core:
The inner core is the innermost layer of the Earth and is located beneath the outer core. It is a solid sphere with a radius of about 1,220 kilometers. Despite the extreme temperatures reaching up to 5,500 degrees Celsius, the immense pressure keeps the inner core in a solid state.

5. Composition and Properties:
The inner core is primarily composed of iron and nickel, similar to the outer core. However, due to the intense pressure at the center of the Earth, the iron in the inner core is in a solid state. It is believed to be even denser than the outer core.

6. Role of the Inner Core:
The inner core plays a crucial role in Earth's structure and dynamics. It is responsible for generating and maintaining the Earth's magnetic field. The movement of molten iron in the outer core, coupled with the solid inner core, creates a dynamo effect that generates the magnetic field protecting our planet.

In conclusion, the innermost layer of the Earth is the Inner Core. It is a solid sphere primarily composed of iron and nickel, located beneath the liquid outer core. The inner core plays a vital role in generating Earth's magnetic field.