In the internal structure of the Earth, the innermost core has an approximate radius of about how many kilometres?

Introduction / Context:

This question concerns basic physical geography, specifically the internal structure of the Earth. The Earth is divided into major layers: crust, mantle and core. Knowing approximate dimensions of these layers helps in understanding geology, seismology and plate tectonics. The question asks for the approximate radius of the Earth innermost core.

Given Data / Assumptions:

• The average radius of the Earth is about 6371 km.
• The Earth core consists of an inner and outer core but is often discussed as a single core region in simple models.
• In school level geography, the radius of the entire core region from the centre up to the core mantle boundary is approximated as about 3500 km.
• The options include values like 500, 6500, 9500, 3500 and 1500 km.

Concept / Approach:

Seismic studies indicate that the core extends from the centre of the Earth outward to a depth of about 2900 km below the surface. Since the total radius of the Earth is about 6371 km, the core radius is approximately 6371 minus 2900, which is close to 3470 km. For simplified learning, this value is rounded to about 3500 km in many textbooks. Therefore, among the provided options, 3500 km is the best approximation for the radius of the core.

Step-by-Step Solution:

Verification / Alternative check:

Most introductory geography and earth science books state that the core extends about 3500 km from the centre. Detailed geophysics resources refine this value to around 3480 km. Since the question clearly seeks an approximate figure, the rounded value of 3500 km is consistent with standard teaching. Other options are either far too small or exceed the total radius of Earth, confirming 3500 km as the correct choice.

Why Other Options Are Wrong:

The value 500 km is much too small and would represent only a small inner region rather than the entire core. The value 6500 km is larger than the overall radius of Earth, which is impossible for a core radius. The value 9500 km is also unrealistic because it exceeds the Earth total diameter. The option 1500 km is closer to estimates for the solid inner core radius, but the question refers broadly to the innermost core region in basic models, where 3500 km is used. Hence these other values are incorrect in this context.

Common Pitfalls:

Students may confuse the Earth radius with core radius, leading to wrong choices like 6500 km. Some may also recall the inner core radius instead of the radius of the whole core region, and choose a smaller value. It is important to recognise that exam questions at this level usually refer to the entire core layer from centre to core mantle boundary, not just the inner core, and provide rounded numbers.

Final Answer:

The approximate radius of the Earth innermost core region is about 3500 km.