However, some have challenged these rocks were not truly from the equator, but that the earth's magnetic poles shifted dramatically sometime in the past, making polar rocks appear as though they were equatorial rocks. Earth's continents have slowly drifted around the globe through the eons, and scientists use magnetic signatures in the rocks to tell where they came from. If the magnetic poles had also moved, it would be impossible to say for sure at what latitude a given rock had formed.
A new study refutes this theory of moving magnetic poles, and bolsters the idea of a "snowball earth."
The research, published recently in the journal Nature, finds that in fact earth's magnetic field has not wandered significantly in the last two billion years and suggests the earth was once an icy planet.