What you will learn in Earth Structure and Interior

1. 1. The deepest hole

   The deepest hole ever drilled reached 12.262 km and did not get a third of the way through the local crust. Everything below it is inference.

2. 2. Two ways to slice a planet

   The Earth has two layer schemes that do not line up, because one is about what the rock is made of and the other about how it behaves. The mantle is solid.

3. 3. Two kinds of wave

   P waves push and pull; S waves shake sideways. Only one of them can cross a liquid, and that single fact is about to find the core.

4. 4. The shadow

   Beyond 103 degrees from any earthquake, no seismometer anywhere records an S wave. The conclusion comes before the explanation.

5. 5. Reading the profile

   Three discontinuities, three names, three different kinds of jump — and the smallest of them is the one that took the most careful reading.

6. 6. Why there is a magnetic field

   Four conditions, all necessary, none sufficient. And the field is not a bar magnet, which is measurable rather than a matter of opinion.