Structure of the Earth, Internal Processes and Weathering – Review Flashcards

Flashcards cover key facts about Earth’s interior structure, including layer composition, temperature, pressure, density gradients, major discontinuities, and distinguishing characteristics of Sial, Sima, mantle, and core.

What are the three major layers of the Earth based on composition?

Crust, Mantle, and Core.

At approximately what rate does temperature increase with depth near the Earth’s surface?

About 1 °C for every 32 metres of descent.

What is the estimated temperature range at a depth of about 48 km?

Roughly 1,200 °C to 2,000 °C.

Which two chemical elements dominate the composition of Sial?

Silicon (Si) and Aluminium (Al).

Which two chemical elements dominate the composition of Sima?

Silicon (Si) and Magnesium (Mg).

Why is Sial considered discontinuous while Sima is continuous?

Sial is lighter and forms continental crust that floats on the heavier, continuous Sima layer under both continents and oceans.

What is the average density of the entire Earth?

About 5.5 g cm⁻³.

What is the Mohorovicic Discontinuity (Moho)?

The boundary between the Earth’s crust and the mantle.

What is the Gutenberg Discontinuity?

The boundary between the mantle and the outer core at about 2,900 km depth.

State the approximate thickness of the Earth’s crust beneath continents.

Roughly 35–48 km, thickest under major mountain ranges.

What two subdivisions make up the mantle?

The Upper Mantle (Asthenosphere) and the Lower Mantle (Mesosphere).

Describe the physical state of the upper part of the asthenosphere.

Partially molten (plastic) allowing slow convection currents.

What elements chiefly compose the Earth’s core?

Nickel and Iron (Ni + Fe, often termed Nife).

Why is the inner core solid despite very high temperatures?

Extremely high pressure (≈3.5 million atmospheres) forces it into a solid state.

Estimate the temperature at the boundary between the molten outer core and solid inner core (~5,100 km depth).

Approximately 4,300 °C.

What is meant by ‘isostatic balance’ in reference to crustal thickness?

The natural balancing of lighter continental crust (thicker under mountains) and denser oceanic crust to maintain gravitational equilibrium.

Define lithosphere.

The rigid outer shell of the Earth consisting of the crust and the uppermost solid mantle.

What rock type is characteristic of the Sial layer?

Granite (granitic composition).

What rock type is characteristic of the Sima layer?

Basalt (basaltic composition).

Give the approximate density values for Sial and Sima.

Sial ≈ 2.7 g cm⁻³; Sima ≈ 2.95 g cm⁻³.

At what approximate depth does pressure reach 1 million atmospheres?

Around 2,500 km below the surface.

What radioactive elements are a significant source of heat in the upper 100 km of the mantle?

Uranium and Thorium.

How thick is the inner core’s radius estimated to be?

About 1,400 km.

What term describes the entire core region in some texts?

Barysphere.