Mantle.
OZONE Layer
STRATOSPHERE
The middle layer of the Earth is called the mantle. It is a region of solid rock that extends from the base of the crust to the outer core. The mantle is composed of silicate minerals and is divided into the upper mantle and the lower mantle.
the layer of rock that comprises 67% of earths mass
half of earths layer
The crust is the thinnest layer of the Earth.
The earth thinnest layer is the crust.
Actually, the Troposphere Layer can be considered as Earth's first protective layer, because its well-the atmosphere's first layer. You can think of it that way to remember which is Earths first layer.
The layer below the earth's outer layer is mesosphere. It is the 3rd layer.
Crust
the earths outer layer
the ozone (O3) layer