Why magnetic poles reverse

They then used climate modelling to find that several major changes coincided with the Laschamp event. The weakened magnetic field allowed more ionising radiation from solar flares and cosmic rays from space to reach Earth. This would have caused extreme weather conditions, including lightning, high temperatures and lots of sunlight — which may have been difficult for organisms to adapt to. Megafauna across Australia and Tasmania — prehistoric giant mammals that existed in the Late Pleistocene — and Neanderthals in Europe went extinct around the same time as the magnetic pole reversal, 42, years ago.

The north pole has been moving spasmodically over the past century, drifting around a kilometre per year, says Cooper. There is simply not enough energy aloft to have an influence on climate down where we live.

Earth is surrounded by a system of magnetic fields, called the magnetosphere. The magnetosphere shields our home planet from harmful solar and cosmic particle radiation, but it can change shape in response to incoming space weather from the Sun.

A constant outflow of solar material streams out from the Sun, depicted here in an artist's rendering. This solar wind is always passing by Earth. It also provides the basis for navigation with a compass. The second image shows changes in that field over the same period. Though the colors in the second image are just as bright as the first, note that the greatest changes were plus or minus nanotesla in a field that reaches 60, nanotesla.

Supercomputer models of Earth's magnetic field. On the left is a normal dipolar magnetic field, typical of the long years between polarity reversals. For reasons not clearly understood, the balance between the effect of the earth's rotation and the effect of temperature on the core dynamo becomes upset from time to time, causing the pattern of the core current to be disrupted.

Following such a disturbance, it is theoretically possible for the dynamo to reconstitute itself with an opposite direction of current flow.

The associated magnetic field, then, will have an opposite polarization. Therefore our knowledge of the core is quite incomplete. We simply don't know enough about the core to predict when pole reversals will occur in the future or how long it takes to complete such a reversal or what upsets the delicate balance of the factors that produce the core current.

But we do have convincing information obtained from magnetized mineral grains in rocks that tells us that geomagnetic polarity reversals have occurred a great many times in the history of the earth. Sign up for our email newsletter.

Already a subscriber? Sign in. Thanks for reading Scientific American. Create your free account or Sign in to continue. See Subscription Options. Discover World-Changing Science. Gary A. He replies: "The Earth's magnetic field is thought to be generated by fluid motions in the liquid, outer part of the Earth's core, which is mainly composed of iron.

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