Until the middle of the 20th century the Earth's magnetism seemed to be a happy accident of nature. Too many factors had to fit just right--the fluid core of the Earth, its electrical condctivity and its motions, all had to satisfy the strict requirements of dynamo theory.
That was before other planets in the solar system were visited and examined. Now we know that among those planets, only Venus lacks any magnetism.
Posted by Jay Roberts at 06:00 PM | Permalink