Credit: minerals. The inner core spins at a different speed than the rest of the planet. Credit: Huff Post Science The freezing of liquid iron into crystalline form at the inner core boundary produces residual liquid that contains more light elements than the overlying liquid.
Scientists recognize patterns in these rocks and sediment, and they can evaluate the composition of rocks and other samples taken from different depths of the Earth during routine excavation and geologic studies in the lab. Currents within the mantle have broken the crust into blocks, called plates, which slowly move around, colliding to build mountains or rifting apart to form new seafloor.
It also means that the Earth's inner core, and the processes that drive it, are far more complex than previously thought!
These are used, along with 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, to determine what Earth's layers looks like. Because we cannot sample the deep Earth, we must deduce its composition either by looking at the clues hidden in igneous and metamorphic rocks, or by examining proxies for composition and structure such as the three-dimensional variation of the velocity of seismic waves produced by earthquakes and sampled by networks of seismometers on the surface.
Recent discoveries also suggest that the solid inner core itself is composed of layers, separated by a transition zone about to km thick. The speed of seismic waves is affected by the properties of the material the waves pass through; the stiffness of material affects the speed of these waves.
For Dr Lineweaver, the next step is to use the type of analysis used in the paper to investigate the composition of the planets around Alpha Centauri, the closest star system to our own. Between this and an inner sphere, he reasoned there was an air gap of the same distance.
Let's take a look at them and see what they have going on.