Magnetic reversals
Observations:
- Magnetic field of Earth reverses on semi-regular basis Short History: 1.0R, 1.8N, 1.9R, 2.5N, 2.9R?,3.1N,3.4R Myrs.
- How do we know dates? Radiocarbon dating; fossils
- “Hot” rocks record the direction of the magnetic field as they cool: Curie Temperature