<P> 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 . Scientific understanding of the internal structure of the Earth is based on observations of topography and bathymetry , observations of rock in outcrop , samples brought to the surface from greater depths by volcanoes or volcanic activity , analysis of the seismic waves that pass through the Earth , measurements of the gravitational and magnetic fields of the Earth , and experiments with crystalline solids at pressures and temperatures characteristic of the Earth 's deep interior . </P>
name the four major layers of the earth in order
an outer silicate solid crust a highly viscous mantle a liquid outer core a solid inner core