The Core

It is the innermost layer, extending from the Gutenberg Discontinuity (Core-Mantle Boundary) at 2900 km to the center of the Earth a 6371 km. Its chemical and physical state dictate the magnetic field and internal heat budget.

Structure

Outer Core

A layer of molten iron alloy, responsible for generating earths magnetic field. The temperature ranges from 4000 K to 5500 K.

Inner Core

Solid sphere of crystalline iron. It is solid despite the high temperatures because of the immense pressure.

Boundary

The boundary between the inner and outer core is the Lehmann Discontinuity. At around 5150 km.

Chemical Composition

The main component is iron with about 5% to 10% nickel. This composition is consistent with the general abundance of these elements in the solar system (derived from CI Chondrites). These siderophile elements, meaning they preferentially partition into the metallic phase during planet formation. Other examples are Gold, Platinum and Palladium, which are mostly stripped from the silicate mantle and concentrated into the core.

Pure Fe-Ni alloys are significantly denser that the actual observed density of the outer core. This requires the presence of lighter elements mixed into the liquid iron. These light elements are Sulfur, Oxygen, Silicon, Carbon and Hydrogen, and make up around 10% of the core.

Heat

The core is incredibly hot, and the heat flow drives the convection in the mantle and the geodynamo in the outer core.

The heat sources are:

• Latent heat of fusion: As the liquid outer core slowly cools and freezes onto the solid core, it releases latent heat.
• Gravitational energy release: The exclusion of light elements from the inner core causes the residual liquid outer core to become less dense, driving convection.
• Radioactive Decay (Minor): radioactive elements are mostly excluded from the core, making the contribution minor.

Question and Answers

What is the primary chemical composition of the Earth's core?::Iron ($\text{Fe}$) and Nickel ($\text{Ni}$) alloy.

The Earth's core is the primary reservoir for what classification of elements?:::Siderophile elements.

What is the range of percentage of Light Elements estimated to be present in the Outer Core?::Approximately $5\mathrm{\%}$ to $10\mathrm{\%}$.

Name the four main candidate light elements thought to be alloyed with iron in the core.::Sulfur ($\text{S}$), Oxygen ($\text{O}$), Silicon ($\text{Si}$), Carbon ($\text{C}$) (or Hydrogen ($\text{H}$)).

The density deficit of the outer core, compared to pure iron-nickel alloy, is attributed to the presence of...?::Light elements.

Which part of the core is liquid and responsible for generating the magnetic field?::The Outer Core.

What is the primary process driving convection (and thus the magnetic field) in the Outer Core?
?
The release of latent heat and gravitational energy as the purer iron alloy of the Outer Core freezes onto the Inner Core, rejecting light elements into the surrounding liquid.