Complex sentence: The interior structure of the Earth is layered in spherical shells: an outer silicate solid crust, a highly viscous mantle, a liquid outer core that is much less viscous than the mantle, and a solid inner core.
Split into simpler sentences: The interior structure of the Earth is layered in spherical shells. Earth has an outer silicate solid crust, a highly viscous mantle, a liquid outer core that is much less viscous than the mantle, and a solid inner core.