A major discovery unfolded over the past five years as it became possible for scientists to compare accurate maps of the geomagnetic field taken 20 years apart.
A major discovery unfolded over the past five years as it became possible for scientists to compare accurate maps of the geomagnetic field taken 20 years apart.
过去五年里，由于科学家终于能够比对相隔20年所观测到地球磁场的准确分布，因而有了重大发现。