One of the key discoveries that led to the widespread acceptance of sea-floor spreading (and
ultimately plate tectonics) was the pattern of “magnetic anomalies” in the oceanic crust.
Shown below is a map of Earth, taken from a publication by Muller et al. (1997) – cited below
— in which the pattern of magnetic anomalies is indicated (referred to as “digital isochrons”
by the authors).
Please examine this map and then answer the questions listed below. It might prove helpful to
review the relevant parts of Chapters 2 & 10 in Lutgens, Tarbuck, and Tasa that deal with
sea-floor spreading (especially §2.9 & 2.10).
For anyone who might be interested, the citation to the original publication appears at the
bottom. You do not have to read that paper to complete the assignment.
(a) What are “magnetic anomalies” and how do they originate?
(b) What is meant by the term isochron?
(c) Based on the distribution of magnetic anomalies, where is the oldest oceanic crust found?
The youngest? What are their ages?
(d) Why is the anomaly pattern in the Atlantic so symmetric, whereas in the Pacific region
(particularly the northern Pacific), it is highly asymmetric?
(e) Why are color bands in the Pacific wider than those in the Atla
