Earth's Interior (Lecture 4)

A set of practice flashcards covering Earth's interior structure, magnetic field, evidence from seismology and drilling, and key geophysical concepts.

What process in the Earth's core generates the magnetic field (the geodynamo)?

Convection of liquid iron in the outer core that sustains the geodynamo.

What is the state of matter of the Earth's mantle and whether it can flow?

The mantle is solid, but it can flow very slowly due to convection.

What are the states of the outer core and inner core?

Outer core is liquid iron-nickel; inner core is solid iron-nickel.

Name the four main internal layers of Earth's interior from outside to inside.

Crust, mantle, outer core, inner core.

Approximate radial thickness ranges for Earth's crust, mantle, outer core, and inner core?

Crust ~0-40 km; Mantle ~40-2890 km; Outer core ~2890-5150 km; Inner core ~5150-6370 km.

What evidence shows there is a liquid layer in Earth's interior?

S-waves cannot travel through liquids, creating S-wave shadow zones; P-waves can travel through.

How are mantle convection and plate tectonics related?

Mantle convection currents drive movement of the lithosphere, leading to seafloor spreading at mid-ocean ridges and broader plate tectonics.

What are mantle xenoliths and why are they important?

Chunks of mantle rocks brought to the surface by rising magma; provide direct mantle samples (e.g., upper mantle peridotite, sometimes lower mantle eclogite).

Name two mantle rock types and what they indicate about the mantle.

Peridotite (upper mantle) and Eclogite (lower mantle; can contain diamond xenocrysts).

What is the crustal geothermal gradient?

Temperature increases by about 25-30°C per kilometer in the crust.

What is the crustal pressure gradient?

Pressure increases by about 25 MPa per kilometer in the crust.

How does density change with depth in Earth?

Density generally increases with depth due to higher pressures and denser materials.

Typical thicknesses of continental vs. oceanic crust?

Continental crust up to ~80 km thick; Oceanic crust about ~7 km thick.

What is the core’s general composition and states of the inner/outer core?

Core is mainly iron (~85-95%) and nickel (~5-6%), with minor impurities; outer core is liquid, inner core is solid.

How is Earth's total heat flow distributed among major layers?

Crust ~24%, Upper mantle ~22%, Lower mantle ~32%, Core ~22%.

What does the S-wave shadow zone tell us about Earth's interior?

It indicates a liquid layer (the outer core) since S-waves cannot travel through liquids.

What is planetary differentiation?

Early in Earth's history, dense heavy elements sank while lighter elements rose, forming the proto-crust and trapping heat inside.

What were Project Mohole and the Kola Superdeep Borehole?

Mohole aimed to drill through the crust to sample the mantle; Kola reached about 12.2 km depth, illustrating drilling limits.

How long does one mantle convection cycle take, and how far has the mantle moved since the pyramids were built?

About 50 million years per convection cell; roughly 16 feet (≈0.005 km) of movement along ~2200 km path since the pyramids.

What are the lithosphere, asthenosphere, and mesosphere in terms of rheology and location?

Lithosphere = crust + upper mantle with brittle rheology; Asthenosphere = central mantle with ductile rheology that can flow; Mesosphere = lower mantle, more rigid due to high pressures.

What role does outer-core convection play in Earth’s magnetism?

Flow of liquid iron in the outer core drives the geodynamo, causing the magnetic field to wander and reversals to occur.

What does the term proto-crust refer to in planetary differentiation?

The early crust that formed as the planet cooled and heat was trapped in the interior.

What is the main takeaway about drilling beyond the upper crust?

We currently do not have the technology to drill beyond Earth's upper crust.