In the internal structure of planet Earth, the core below the mantle is composed mainly of which chemical element?

Introduction / Context:
Earth interior is divided into layers, including the crust, mantle and core. The core itself is further divided into an outer liquid part and an inner solid part. This question asks which element is the main component of the core, a key fact in physical geography and Earth science.

Given Data / Assumptions:

• The focus is on the composition of Earth core, which lies beneath the mantle.
• Options list aluminium, chromium, iron, silicon and copper.
• We assume the standard model of Earth interior based on seismic and density evidence.
• We want the dominant element, not minor components or alloying elements.

Concept / Approach:
Studies of seismic waves, Earth gravity and average density show that the core must be made of a dense metal. The best match for these observations is iron with some nickel and lighter elements. Iron is abundant in the universe and forms the central part of many planets. Therefore, iron is recognised as the primary component of both the liquid outer core and solid inner core.

Step-by-Step Solution:
Step 1: Recall the density of Earth and compare it with the densities of crustal rocks. The average density is higher than that of the crust, indicating a heavy interior.Step 2: Seismic wave behaviour suggests a large, dense core. The type of waves that travel through solids and liquids show that the outer core is liquid and the inner core is solid.Step 3: Iron has a high density and is common in meteorites, which are used as analogs for Earth internal composition.Step 4: Aluminium and silicon are major components of the crust and upper mantle, not of the core. Chromium and copper are present only in smaller amounts.Step 5: Therefore, the core beneath the mantle is mainly made up of iron.

Verification / Alternative check:
Geophysics textbooks describe Earth as having an iron nickel core surrounded by a silicate mantle. Laboratory experiments on metals at high pressure and temperature support this model. The behaviour of seismic P waves and S waves as they cross the core mantle boundary also fits the idea of a metallic core dominated by iron. No alternative composition based on aluminium, silicon or copper matches the observed data as well.

Why Other Options Are Wrong:
Aluminium and silicon are key elements in crustal rocks such as granite and basalt but are not dominant in the core. Chromium and copper occur in ores within the crust and mantle but in much smaller amounts than iron. None of these elements can provide the required density and magnetic properties of the core. Only iron, with some nickel, fits as the main core material.

Common Pitfalls:
Some learners see silicon frequently in the context of silica and silicate rocks and think that all parts of Earth must be silicon rich. Others may choose aluminium because of the term sial for continental crust. These confusions arise from mixing up layers. Remember that light elements, including silicon and aluminium, dominate the crust, while heavy metals like iron sink toward the centre during planetary formation and form the core.

Final Answer:
Earth core below the mantle is composed mainly of iron.