GS-1: Geo-magnetism ,Geo-morphology

Why in news?

• Recent discoveries show that the Excursion and Wandering of magnetic poles is speeding up — about 50 km a year. The magnetic North, which drifts, lies some 500 km south of the geographic North, in the Ellesmere Island, northern Canada.

So are we experiencing a magnetic reversal?

• Measurements have been made of the Earth's magnetic field more or less continuously since about 1840.
• Some measurements even go back to the 1500s, for example at Greenwich in London. If we look at the trend in the strength of the magnetic field over this time (for example the so-called 'dipole moment' shown in the graph below) we can see a downward trend.
• Indeed projecting this forward in time would suggest zero dipole moment in about 1500-1600 years time. This is one reason why some people believe the field may be in the early stages of a reversal.
• We also know from studies of the magnetisation of minerals in ancient clay pots that the Earth's magnetic field was approximately twice as strong in Roman times as it is now.
• Even 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.
  Also, bearing in mind what we said about 'excursions' above, and knowing what we do about the properties of mathematical models of the magnetic field, it is far from clear we can easily extrapolate to 1500 years hence.

Is there any danger to life?

• Almost certainly not. The Earth's magnetic field is contained within a region of space, known as the magnetosphere, by the action of the solar wind.
• The magnetosphere deflects many, but not all, of the high-energy particles that flow from the Sun in the solar wind and from other sources in the galaxy.
• Sometimes the Sun is particularly active, for example when there are many sunspots, and it may send clouds of high-energy particles in the direction of the Earth. During such solar 'flares' and 'coronal mass ejections', astronauts in Earth orbit may need extra shelter to avoid higher doses of radiation.
• Therefore we know that the Earth's magnetic field offers only some, rather than complete, resistance to particle radiation from space. Indeed high-energy particles can actually be accelerated within the magnetosphere.
• The magnetosphere deflects many, but not all, of the high-energy particles that flow from the Sun in the solar wind and from other sources in the galaxy.
• Sometimes the Sun is particularly active, for example when there are many sunspots, and it may send clouds of high-energy particles in the direction of the Earth. During such solar 'flares' and 'coronal mass ejections', astronauts in Earth orbit may need extra shelter to avoid higher doses of radiation.
• Therefore we know that the Earth's magnetic field offers only some, rather than complete, resistance to particle radiation from space. Indeed high-energy particles can actually be accelerated within the magnetosphere.
• Human beings and their ancestors have been on the Earth for a number of million years, during which there have been many reversals, and there is no obvious correlation between human development and reversals.
• Similarly, reversal patterns do not match patterns in species extinction during geological history.
• Some animals, such as pigeons and whales, may use the Earth's magnetic field for direction finding. Assuming that a reversal takes a number of thousand years, that is, over many generations of each species, each animal may well adapt to the changing magnetic environment, or develop different methods of navigation.
• Further, no one quite really knows how a change in earth’s magnetic field might affect these satellites.

What is Wandering, Excursion and Reversal of earth’s magnetic field?(See image)

• The Earth's magnetic field is similar to that of a bar magnet tilted 11 degrees from the spin axis of the Earth. The Earth's magnetic field is attributed to a dynamo effect of circulating electric current, but it is not constant in direction.
• By magnetic reversal, or 'flip', we mean the process by which the North pole is transformed into a South pole and the South pole becomes a North pole. In the last 10 million years, there have been, on average, 4 or 5 reversals per million years. At other times in Earth's history, for example during the Cretaceous era, there have been much longer periods when no reversals occurred.
• Interestingly, the magnetic field may sometimes only undergo an 'excursion', rather than a reversal. Here, it suffers a large decrease in its overall strength, that is, the force that moves the compass needle. During an excursion the field does not reverse, but later regenerates itself with the same polarity, that is, North remains North and South remains South.
• Polar wandering, the migration of the magnetic poles over Earth’s surface through geologic time

Source: The Hindu BL

Q. Consider the following questions regarding earth’s magnetic field.

1. It’s is created by what we call the “ Dynamo Effect”.
2. It flips very regularly in millions of years of time period.
3. In the past, reversal of magnetic field has led to mass extinction.

Which of the above statements above is/are incorrect?

a) 1 only

b) 1 and 2 only

c) 2 and 3 only

d) All of the above

Ans. c)

Q. Earth’s magnetic field has flipped (reversed) very often in the geological past and now some scientists are of the view that the earth is soon going to flip its magnetic directions. What are the evidences in favour and in against of this view? Enumerate. What could be the adverse implication of such reversal on life forms inhabiting the planet?