- 3362 - EARTH’S - magnetic core is moving? Though the Earth’s magnetic field is very similar to that of a bar magnet, with a north and south pole, it is not as stable because it is generated by complex processes inside the Earth. These cause the magnetic poles to wander.
--------------------- 3362 - EARTH’S - magnetic core is moving?
- Magnetic fields are generated by electric charges in motion. In a bar magnet, the moving charges are electrons orbiting in atoms. In the Earth, they are electrons in circulating currents of molten iron.
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- Hot material in Earth’s outer liquid iron core expands, becoming less dense than its surroundings, and therefore rises. Cooling and becoming less dense, it should sink back down again. But, the Earth’s rotation prevents this.
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- Consequently, liquid circulates around the core, and friction between its different layers charges them up just like a plastic comb rubbing against a nylon sweater. It’s these moving charges that generate the Earth’s magnetic field.
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- The two requirements for planetary magnetism are therefore a liquid core and rotation. We know this because Venus, though roughly Earth’s size, has essentially no magnetic field. The planet has a liquid core but rotates slowly, only once every 243 Earth days.
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- Why do Earth’s magnetic poles move? Though the Earth’s magnetic field is very similar to that of a bar magnet, with a north and south pole, it is not as stable because it is generated by complex processes inside the Earth. These cause the magnetic poles to wander.
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- Historically, the North Pole has moved at about 15 kilometers per year. But since the 1990s it has sped up, and now is moving at about 55 kilometers per year towards Siberia. It is speculation, but this might foreshadow a ‘magnetic reversal’ in which the magnetic north and south poles change locations. This has happened 171 times in the past 71 million years, and, we are overdue for a flip.
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- Models of the Earth’s magnetic field based on satellite observations have shown that the present wandering is the result of a battle between ‘blobs’ of unusually intense magnetic fields deep inside the planet.
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- What would happen if the magnetic field disappeared? Scientists discovered magnetic reversals by measuring the magnetic field on either side of mid-Atlantic ridges from which molten rock is extruded like toothpaste from a tube. As it solidifies, its crystals align along the direction of the Earth’s magnetic field at the time, leaving a ‘tape recording’ of reversals.
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- Reversals are believed to take place over 1,000 to 10,000 years, during which time the field shrinks to zero before growing again with the opposite polarity. There were therefore times, maybe even centuries, when the Earth had essentially no magnetic field.
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- This is dangerous for life since the planet’s magnetic field extends far into space and creates a protective bubble around Earth, shielding the planet’s surface from the hurricane of particles of the Sun’s ‘solar wind’ and higher energy ‘cosmic ray’ particles from deep space.
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- Normally, these particles are safely funneled down at the poles, creating the “auroras“ (Northern Lights ). Without a protective field, such deadly radiation would increase the mutation rate of living cells, leading to cancers in animals. Nevertheless, life has weathered large numbers of such events before without being wiped out.
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- How stable is Earth’s magnetic field? The fact that the Earth’s magnetic field depends on electric currents carried by molten material circulating in the planet’s turbulent interior means it is inherently variable, as demonstrated by the present wandering of the magnetic north pole (the magnetic south pole is, surprisingly, not wandering as fast).
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- What is remarkable is that the magnetic field generated by such violent internal convulsions is relatively stable 99.9 per cent of the time. It is the stability of the Earth’s magnetic field, and the reliability of the protection it has provided, that has enabled life on Earth to persist for almost at least 3.8 billion years.
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- How do animals use the magnetic field to navigate? Many creatures demonstrate remarkable feats of navigation. The suspicion has therefore arisen that they have some kind of magnetic sense, enabling them to detect the magnetic field lines between the poles. Pinpointing the mechanism, however, has proved difficult. But progress has been made in 2021 by Japanese scientists investigating a process discovered many years ago.
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- In the 1970s scientists observed single-celled organisms streaming in a fixed direction in a muddy pond and showed they were responding to a magnetic field. Biologists later discovered that such single-celled organisms contain tiny bags of magnetic iron oxide or iron sulphide.
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- They have shown that a magnetic field causes chemical changes that can affect cellular behavior. They achieved this with the aid of a cellular chemical that fluoresces depending on the external magnetic field. When they waved a magnet near cells, the chemical dimmed by up to 3.5 per cent.
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- From the study of seismology which is the measurements of sound waves traveling through Earth we can tell that the core is molten. Plus, from our knowledge of the abundance of elements in the Universe and how they behave, we think it’s made mainly of iron under huge amounts of pressure.
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- All this indicates its temperature is about 6,000°C, similar to the temperature of the Sun’s surface. And Earth’s core is only 3,000 kilometers from its surface. So why doesn’t Earth’s core fry us all? Because the core is surrounded by a mostly solid mantle of rock.
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- The crust we live on floats on that mantle, giving us more protection. But the most important reason we don’t all melt is the difference between heat and temperature. Roughly speaking, heat is energy and temperature is density of energy, basically how much energy is crammed into a given size.
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- A spark from a sparkler can have a temperature of 1,500°C, but won’t really hurt you. On the other hand, a bath of boiling water at only 100°C would kill you. That’s because the bath contains much more heat energy.
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- To melt the whole Earth, you would need much more energy than the heat in its core. The Sun is huge and could easily do that, but, luckily it’s 150,000,000 kilometers away.
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- The Earth’s axis isn’t perfectly upright relative to its orbit, but instead is tilted at an angle of around 23.5°. This so-called obliquity has long been known to change slightly over thousands of years as a result of the gravitational influence of the Sun, the Moon and the other planets.
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- But evidence is also emerging for effects resulting from climate change. In 2013, researchers reported that satellite measurements had revealed that the Earth’s tilt is being affected by the shift in mass caused by the melting of ice covering Greenland.
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- The team found that around 15 years ago the Earth’s axis began to move east and then south. Earlier this year, researchers confirmed the effect, and added another cause: changes in the amount of water stored in the Earth’s continents. Lower rainfall over Europe and Asia in recent years seems to be adding to the axial drift.
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- So is man-made global warming to blame for these changes? It’s probably just part of the Earth’s natural climatic rhythms. Either way, the effect isn’t anything to lose sleep over: the recent shift amounts to less than one-millionth of the Earth’s total tilt angle.
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- You probably would not notice this tilt or axial drift. You would get more of this effect drinking too much alcohol.
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November 29, 2021 EARTH’S - magnetic core is moving? 3362
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