In the structure of the Earth, the outermost solid layer is called which of the following?

Introduction:
Understanding the layered structure of the Earth helps explain many geological processes. This question again focuses on naming the outermost solid layer of the Earth. Although similar to earlier questions on the crust, it reinforces the same core concept that is often tested.

Given Data / Assumptions:

• The question refers to the structure of the Earth.
• The outermost solid layer is being named.
• Options include sphere, crust, mantle, core, and asthenosphere.
• We assume a simple division into crust, mantle, and core along with related terms.

Concept / Approach:
The Earth is broadly divided into crust, mantle, and core. The crust is the thin outer shell where continents and ocean floors are located. Beneath it lies the mantle, and deeper inside is the core. The asthenosphere is a zone within the upper mantle where rocks are partially molten and can flow slowly. Sphere is a general geometric term and not the name of a specific layer. Therefore, the correct name for the outermost solid layer is crust.

Step-by-Step Solution:
Step 1: Recall the standard labels for Earth layers: crust, mantle, and core.Step 2: Identify that the layer directly under the atmosphere is the crust.Step 3: Recognise that mantle is a deeper layer and core is the innermost part.Step 4: Note that asthenosphere is part of the upper mantle and not the outermost rock layer.Step 5: Choose crust as the correct answer.

Verification / Alternative check:
Diagrams in geography and geology books show the crust as a very thin outer ring, the mantle as a thick middle layer, and the core as the central region. Some diagrams also label the asthenosphere just below the lithospheric plates within the upper mantle. These visual aids confirm that crust is the outermost solid layer.

Why Other Options Are Wrong:
Sphere is not a recognised geological layer; it simply describes the general shape of the Earth. Mantle is a thick layer beneath the crust and cannot be the outermost. Core is the deepest part of the Earth, divided into outer and inner core, and lies far below the surface. Asthenosphere is a semi molten region within the upper mantle and is not exposed at the surface.

Common Pitfalls:
Some learners may confuse lithosphere and asthenosphere. The lithosphere includes the crust and the uppermost part of the mantle and forms the tectonic plates. Asthenosphere lies beneath the lithosphere. However, in many school level questions the simplest correct label for the outer solid layer is crust. Keeping this in mind prevents unnecessary confusion.

Final Answer:
Correct option: Crust