Earth's inner core

Earth’s innermost solid layer, composed primarily of iron and nickel and surrounded by the liquid outer core. Its extreme pressure keeps it solid despite temperatures comparable to the Sun’s surface.

Seismic waves: Elastic disturbances that carry energy through Earth and other materials. Their changing speeds and paths reveal the inner core’s size and physical state.
Earth's internal structure: The arrangement of Earth into layers with distinct compositions and physical properties. The inner core is the deepest layer in this model of Earth.
Earth's formation: The process by which Earth assembled from material orbiting the young Sun about 4.5 billion years ago. Differentiation during Earth’s early history concentrated iron at the center.
Inner-core anisotropy: The directional dependence of seismic-wave speeds within Earth’s inner core. Its pattern may record how iron crystals are aligned or how the inner core formed.
Earth's crust: Earth’s thin, solid outermost rocky layer. The crust is accessible and silicate-rich, unlike the deep, metallic inner core.
P waves: Compressional seismic waves that travel through solids and liquids. Their passage through the inner core provides direct evidence that it is solid.
Earth's core: Earth’s central region, made mostly of iron and nickel and divided into liquid and solid parts. The inner core is the solid part of the broader metallic core.
Planetary differentiation: The separation of a forming planet into layers according to the density and chemical behavior of its materials. Dense iron sank inward, creating the metallic core from which the inner core later formed.
Inner-core rotation: The rotation of Earth’s inner core relative to the mantle and crust. Seismic studies disagree about whether and how its relative rotation changes over time.
Mars's core: The central metallic region of Mars, which is largely liquid and contains substantial light elements. Mars lacks Earth’s clearly established solid inner core, offering a different planetary evolution.

Linked from 7 pages