Concept:The Lehmann discontinuity is the seismic boundary found in the deepest region of the Earth, separating the outer core from the inner core.
Explanation:The Earth is composed of four major layers: the crust, the mantle, the outer core, and the inner core.
These layers are separated by transition zones known as discontinuities.
From the surface moving inward, the main discontinuities are: the Conrad discontinuity (between upper and lower crust), the Mohorovicic discontinuity (between crust and mantle), the Repiti discontinuity (between outer and inner mantle), the Gutenberg discontinuity (between mantle and core), and finally the Lehmann discontinuity (between outer core and inner core).
Because the inner core is the central part of the Earth, the Lehmann discontinuity lies at the innermost boundary.
It was discovered by the Danish seismologist Inge Lehmann in 1936.
This discontinuity is identified by sudden changes in the velocity of seismic waves, which indicate differences in material properties and physical structure.
Thus, among the given options, the Lehmann discontinuity marks the innermost part of the Earth.
Answer:Lehmann discontinuity