How we know the Earth has a liquid outer core
PAPER III — PHYSICS · QUESTION 34 OF 35
In plain terms: The free official book on how the Earth’s interior was worked out without anyone going there.
The question as set
How do we know the Earth has a liquid outer core? Argue from the S-wave shadow zone, and quantify what the observation constrains.
The question in Paper III · Its section on the reference page
The question in context
This is question 34 of the 35 set in Paper III — Physics of The Truly Hardest Exam in the World, the examination of The College of All Minds. In the College’s subject index it is filed under Seismology and the Earth’s interior. Like every question of the College, it carries three references of record, verified live at publication and described twice — technically, and in plain terms — so the ground can be judged before it is walked. The response required is an argument, not a survey, of at most three thousand words, as technical as the question demands and no more.
The references of record
The seismological evidence assembled: travel times, shadow zones, and the layered model they force.
In plain terms: The free official book on how the Earth’s interior was worked out without anyone going there.
Seismic wave behaviour — the shadow zone
The inference set out: S-waves absent beyond 103°, P-waves refracted — shear rigidity ruled out for the outer core.
In plain terms: The free animation and note that make the classic argument step by step.
The instrumental basis: global networks, phase picking, and the data from which interior structure is inverted.
In plain terms: The free official account of the seismic record that the argument depends on.
Background: Shadow zone · Internal structure of Earth