Which of the following statements concerning the Earth’s internal structure, magnetic field, or heat transfer within the Earth is FALSE?

Question

BlackTom AI · Accepted Answer

Earth's magnetic field is generated by the geodynamo: convective motion of electrically conducting fluid in the liquid outer core combined with Earth's rotation (Coriolis forces) and electrical conductivity produce and sustain the field. However, saying that an entirely liquid core would make the field "much greater" is incorrect.

Relevant knowledge points:
- Geodynamo requires fluid motion, but also a source of buoyancy (thermal and compositional) and boundary conditions that sustain organized convection and field amplification.
- The inner core is solid and its gradual crystallization releases latent heat and ejects lighter elements into the outer core; these processes drive compositional convection, a key energy source for the geodynamo.
- Heat transfer: within Earth, conduction and slow solid-state convection dominate the mantle; fluids can transport heat through fractures and porous layers in the crust; at the surface, radiation is the primary mechanism for losing heat to space.
- Magnetic reversals recorded in seafloor basalt document seafloor spreading but do not cause plate motions (which are driven by mantle convection, slab pull, ridge push).

Step-by-step reasoning:
1. The outer core being liquid is necessary but not sufficient for a strong geodynamo.
2. The solid inner core contributes critically by releasing latent heat and light elements as it freezes; this compositional buoyancy enhances convection vigor in the outer core.
3. If the entire core were liquid (no inner core growth), those buoyancy sources would be diminished; thermal convection alone could be weaker or organized differently, possibly reducing field strength and stability.
4. Empirical and theoretical work indicates that the inner core's presence helps sustain a strong, long-lived magnetic field; losing it would not automatically increase the field.

Why other options are correct:
- Heat in the crust moves mainly by conduction or by fluid advection along fractures/porous layers — true (hydrothermal flow is important).
- Magnetic reversals recorded in seafloor rock confirmed seafloor spreading but do not drive plate motions — true.
- The solid mantle transfers heat by conduction and slow (solid-state) convection — true.
- Radiation is how Earth loses heat to space at the surface, but radiation is negligible for internal heat transfer due to opacity and density — true.

Therefore the FALSE statement is: "The Earth’s magnetic field is caused by convection of its outer core, so if its entire core were liquid, its magnetic field would be much greater." This matches the provided answer.

Which of the following statements concerning the Earth’s internal structure, magnetic field, or heat transfer within the Earth is FALSE?单项选择题

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