Question

retains heat from the planets formation.

1. inner core: at the very center, theres the solid and dense inner core, primarily composed of metal.

its important to note that the earths structure is not static but is always changing. for example, the lithospheres tectonic plates are always moving which causes earthquakes, mountain building, and volcanoes.
what is the earths outermost solid layer?
inner core
lithosphere
upper mantle

Explanation:

The lithosphere is the rigid, outermost shell of the Earth. It consists of the crust and the uppermost part of the mantle. The inner core is at the center of the Earth, not the outermost layer. The upper mantle is below the lithosphere.

Answer:

lithosphere