I just watched a documentary on the history of the Earth's magnetic field that was very interesting. It said that the Earth historically has averaged a pole flip roughly every 200,000. However, Earth has not flipped its poles in over 700,000 as evidenced by ferromagnetic iron samples taken from varying altitudes of volcanoes all over the world. Essentially the process is like this, when magma cools to a certain temperature, the iron in it, which is ferromagnetic (aka. the iron is divided into finely divided sections which each carry a magnetic dipole moment in random directions), is acted upon by the Earth's magnetic field at the moment of cooling and therefore the iron's finely divided sections all take on the same North / South 'compass' direction as the Earth currently had at the time. So you see, by radiometric dating and establishment of the age of the magma from where the iron came from, you can simply check the direction of their dipole moments and whence after taking many samples, track the points in time when the poles flipped! It should be noted that the radiometric dating methods used have large error factors when predicting the date of the magma's cooling, yet still the rough interval between pole flips i quoted as 200,000 years gives you a good sense of a reasonable time scale in which pole flips occur on average. Clearly, if we are in the midst of the beginnings of a current pole flip (we are ~500,000 years overdue anyhow), its power to reverse the seas and melt the icecaps will most assuredly outshadow any of the human environmental vices that impact our Earth's current global warming. In short, our ills upon nature are still juvenile compared to nature's ill upon itself. What do you think?