| A | B |
|---|
| underwater mountain range | mid-ocean ridge |
| rift | crack |
| young ocean material is found here | closest to the ridge |
| old ocean crust is located here | nearest the trenches |
| trench | large crevice where old ocean material is consumed |
| paleomagnetism | the study of the magnetic properties of ancient rocks |
| echo-sounding devices | mapped the ocean floor |
| Harry H. Hess | scientist who proposed theory of sea-floor spreading |
| Glomar Challenger | research vessel that driills into the ocean floor and determines the age of the ocean floor |
| 180 million years | oldest oceanic rock material |
| iron | minerals in basalt that align themselves according to the magnetic field orientation at the time they form |
| magnetometer | instrument that records magnrtic data |
| lithosphere | solid outer layers of the earth consisting of 20 plates |
| asthenosphere | plastic-like upper mantle |
| magnetic poles | reversals of these are shown in the rock along the midocean ridges |
