Q: I watched a programme about how tectonic plate movements mean the continents are moving by an average of 3cm a year.
There was a picture of Pangaea starting to 'break up' and a caption of 250 million years ago. If the circumference at the equator is approx 6,380km, then does this mean the land masses have moved around the world over a hundred times?
It is rather confusing for a novice as all the images I have seen (animated and still) don't indicate any movement beyond one area, it looks like the continents have just moved around on the same side of the earth.
From Ms Jeannie Cooper (October 2010)
Reply by Dr Ted Nield (Editor, Geoscientist)
I cannot fault your arithmetic, and you reach a conclusion that is not, in fact, far from the truth - though the scale of the answer is perhaps a little exaggerated.
Pangaea began to break up about 250 million years ago. However it was only the latest in a long series of supercontinents to form on Earth as the drifting continents came together repeatedly in a cycle that lasts about 500 million years from end to end. So at the moment we are half way through the present cycle. In another 250 million years a new supercontinent will form. Supercontinents hold together for roughly 100 million years – hence part of the inherent exaggeration in your equation. Also, spreading rates vary enormously from about 1cm per year at the slowest (Gakkel Ridge, Arctic Ocean) to as much as 15cm per year (East Pacific Rise).
Before Pangaea, at about 1000 million years ago, another supercontinent occupied equatorial regions and has been called Rodinia. It is the continent on which early complex life first evolved (hence its name, from the Russian for “motherland”). There has been a succession of such cycles since plate tectonics first began, shortly after the formation of the earth 4567 million years ago - though of course the farther back one goes, the dimmer the light that the rock record sheds.