A few people have commented on our palaeogeographic maps asking if they are upside down or not, and

A few people have commented on our palaeogeographic maps asking if they are upside down or not, and how do we know that was the position of the continents; so we’re going to explain this below. The science behind creating these maps is called “palaeomagnetics”, and this science uses iron bearing minerals in sedimentary and igneous rocks to track the position of magnetic North in the geological past. We know that during the geological past the Earth has experienced what are known as “Geomagnetic Reversals” and this basically means the North Pole has become the South Pole and vice versa. Sometimes the magnetic field may not flip, it may just suffer an overall decrease in strength (known as an excursion). Geomagnetic reversals were first discovered when looking at the rocks associated with sea-floor spreading in the Atlantic Ocean. Geomagnetic reversals happen with differing frequency throughout geological history, but scientists have mapped 184 reversals in the past 83 million years. When there are no reversals in a 10million year period, it is known as a superchron. There are 2 known superchrons, one from the Cretaceous period lasting 40 million years and another that lasted over 50 million years, from the late Carboniferous (the Pennsylvanian for American Geologists) to the late Permian. So how is this information trapped in the rocks? When igneous rocks cool, the iron bearing mineral crystals in the magma align themselves with the Earth’s magnetic field, and when the rock cools completely these minerals permanently display the direction of the Earth’s magnetic field at the time the rock was formed. The rocks not only record the direction of the Earth’s magnetic field, they also record the inclination and this is where the palaeolatitude information comes from. -LL Links for more information;http://www.earth.ox.ac.uk/research/groups/magnetism/publicationshttp://www.geomag.bgs.ac.uk/education/reversals.htmlhttp://deeptow.whoi.edu/gpts.htmlhttp://www.thisoldearth.net/Geology_Online-1_Subchapters.cfm?Chapter=3&Row=4 -- source link
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