![]() Perhaps more than one North and South pole at any given time. Run on supercomputers, a far more complicated field pattern at the Earth's surface, with We might expect to see, based on models of the field What happens during a reversal? What do we see at the Earth's surface?Īs above, we have limited evidence from geological measurements about the patterns of change Standards but slow on a human time scale.īack to the top. May take about one to several thousand years to complete. For example, the mathematical simulations seem to suggest that a full reversal Mostly on the basis of mathematical models of the field behaviour and partly on limitedĮvidence from rocks that retain an imprint of the ancient magnetic field present when they We have no complete record of the history of any reversal, so any claims we can make are Of mathematical models of the magnetic field, it is far from clear we can easily extrapolateīack to the top. In mind what we said about 'excursions' above, and knowing what we do about the properties Pots that the Earth's magnetic field was approximately twice as strong in Roman times asĮven so, the current strength of the magnetic field is not particularly low in terms of the range of values it has had over the last 50,000 years and it is nearly 800,000 years since the last reversal. We also know from studies of the magnetisation of minerals in ancient clay This is one reason why some people believe the field may be in the early stages Indeed projecting this forward in time would suggest zero dipole moment in about 1500-1600 The so-called 'dipole moment' shown in the graph below) we can see a downward trend. If we look at the trend in the strength of the magnetic field over this time (for example Some measurements even go back to the 1500s, for example at Greenwich in London. Measurements have been made of the Earth's magnetic field more or less continuously sinceĪbout 1840. Is the Earth's magnetic field reversing now? How do we know? ![]() Hence we can only speak about the average reversal interval.īack to the top. Reversals are not predictable and are certainly not periodic in nature. At other times in Earth's history,įor example during the Cretaceous era, there have been much longer periods when no On average, 4 or 5 reversals per million years. In the last 10 million years, there have been, We can see this in the magnetic patterns found in volcanic rocks, especially That is, North remains North and South remains South.Īs a matter of geological record, the Earth's magnetic field has undergone numerous reversals DuringĪn excursion the field does not reverse, but later regenerates itself with the same polarity, Here, it suffers a largeĭecrease in its overall strength, that is, the force that moves the compass needle. May sometimes only undergo an 'excursion', rather than a reversal. Into a South pole and the South pole becomes a North pole. Northern hemisphere and one in the Southern hemisphere.īy magnetic reversal, or 'flip', we mean the process by which the North pole is transformed Say that there are currently two poles observed on the surface of the Earth, one in the However there is much small-scale variation in theĮarth's field, which is quite different from that of a bar magnet. It is often described as being similar in nature to theįield of a bar (e.g. At these places, a compass needle will point That it has one North pole and one South pole. The magnetic field is largely that of a dipole, by which we mean Generated in the very hot molten core of the planet and has probably existed throughout most The Earth has a magnetic field, as can be seen by using a magnetic compass. What do we mean by a magnetic reversal or a magnetic 'flip' of the Earth? Links to other descriptions of the Earth's magnetic field.I'm interested in a more technical description. ![]() What happens during a reversal? What do we see at the Earth's surface?.Is the Earth's magnetic field reversing now? How do we know?.What do we mean by a magnetic reversal or a magnetic 'flip' of the Earth?.
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