Short answers, pulled from the story.
The internal structure of Earth is a series of layers. Mechanically it consists of a rigid lithosphere, a semi-fluid asthenosphere, a rigid mesosphere, a liquid outer core, and a solid inner core. Chemically it is a silicate crust, a ferromagnesian mantle, and an iron-nickel core.
Scientists infer the internal structure of Earth indirectly using the travel time of refracted and reflected seismic waves from earthquakes. They also study topography, rock outcrops, samples from volcanoes, gravitational and magnetic field measurements, and laboratory experiments on crystals at deep-interior pressures and temperatures.
Earth's mantle extends to a depth of 2,890 kilometres, making it the planet's thickest layer. That depth is 45 percent of the 6,371 kilometre radius, and the mantle accounts for 83.7 percent of Earth's volume.
Earth's inner core was discovered in 1936 by Inge Lehmann. It is a solid ball with a radius of about 1,220 kilometres, composed primarily of iron with some nickel, and its solidity is shown by its ability to transmit shear waves.
Earth's crust ranges from 5 to 70 kilometres in depth and is the outermost layer. The oceanic crust beneath ocean basins is 5 to 10 kilometres thick, while the thicker, less dense continental crust is rich in felsic minerals such as feldspar and quartz.
Dynamo theory suggests that convection in Earth's liquid outer core, combined with the Coriolis effect, generates the planet's magnetic field. The average magnetic field in the outer core is estimated at 2.5 millitesla, fifty times stronger than the field at the surface, and it protects life from interplanetary radiation.