Which layer is considered Earth's outermost layer?

The crust is considered Earth's outermost layer because it is the thin, solid shell that forms the surface of the planet. The crust is composed of a variety of rocks and minerals and is divided into continental and oceanic regions. Continental crust is thicker and forms the landmasses, while oceanic crust is thinner and lies beneath the oceans.

The core, while crucial to Earth’s structure, lies deep beneath the crust and is made up primarily of iron and nickel. The mantle is situated below the crust and is composed of semi-solid rock that flows slowly over geological timescales. The asthenosphere is a layer within the upper mantle that behaves in a ductile manner, allowing the tectonic plates of the crust to move over it. Thus, the crust is distinctly identified as the outermost layer.