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Earth is has it's own protective magnetic shield, called the magnetosphere. The magnetosphere blocks much of the harmful solar and cosmic particle radiation. This magnetic field is immense, but actually quite weak, only about 1 Faraday in strength. But did you know that our magnetic field reverses itself every so often? The north pole becomes the south pole and vice versa. Earth's magnetic pole reversals have happened throughout Earth's history. The last one occurred 780,000 years ago.
The drawing shows the dynamo mechanism that creates Earth's magnetic field: convection currents of fluid metal in Earth's outer core, which are driven by heat flow from the inner core, organized into rolls by the Coriolis force, create circulating electric currents, which generate the magnetic field. Credit: Andrew Z. Colvin, CC BY-SA 4.0, via Wikimedia Commons.
The invisible lines of the magnetic field travel in a closed, continuous loop, flowing into Earth at the north magnetic pole and out at the south magnetic pole. The solar wind compresses the field’s shape on Earth’s Sun-facing side, and stretches it into a long tail on the night-facing side. See the 2 diagrams at right showing the effects of the solar wind on the shape of earth's magnetic field.
The magnetosphere shields us from our atmosphere being stripped away by solar wind, particle radiation from coronal mass ejections (eruptions of large clouds of energetic, magnetized plasma from the Sun’s corona into space), and from cosmic rays that come from deep space.
Without a functioning magnetosphere, earth would rapidly become like Venus, a boiling hot planet, lacking water and an atmosphere. The current theory is that Venus' magnetosphere stopped and it's atmosphere and water were blown away by the solar wind.
Earth’s magnetosphere experiences periodic pole reversals. During a pole reversal, Earth’s magnetic north and south poles swap locations. Sir James Clark Ross first discovered the North Magnetic Pole in northern Canada in 1831.
Since 1831, the pole has been moving across the Canadian Arctic toward Russia. NCEI scientists with the Cooperative Institute for Research in Environmental Sciences (CIRES) at the University of Colorado Boulder calculated the movement of both the North and South Magnetic Poles from 1590 to 2025.
Paleomagnetic records show us that Earth’s magnetic poles have reversed 183 times in the last 83 million years, and at least several hundred times in the past 160 million years. The time intervals between reversals varies, but average about 300,000 years, with the last reversal taking place about 780,000 years ago. The reversal can take about 1,000 years to complete. The last reversal occurred between 772,000 and 774,000 years ago. Since then, the field has almost reversed 15 times, called an excursion, dropping in strength significantly but not quite reaching the threshold needed before rising again.
The reversal it leaves fossilised magnetisation in rocks on Earth. In other words, it leaves a permanent unique magnetic record in the fossils, which can be dated. By taking cores samples of sediments from the sea floor, like a long straw that can extend down up to 300 metres with the help of a drill, we can look back in time and see when these reversals occurred.
Here's how it works:
When the tectonic plates form along the oceanic ridges, the magnetic field that exists is “frozen” into the rock as they cool below about 700°C. The slowly moving plates act as a kind of tape recorder leaving information about the strength and direction of past magnetic fields. By sampling these rocks and using radiometric dating techniques, it has been possible to reconstruct the history of Earth's magnetic field for roughly the last 160 million years.
If one “plays the tape backwards,” the record shows Earth’s magnetic field strengthening, weakening, and often changing polarity.
Scientists don’t know what causes pole reversal or why it occurs at an inconsistent frequency, but they speculate that it may be due to convection processes within the Earth’s mantle.
As Earth's magnetic shield pauses and reverse, it is thought likely that it could causes malfunctions in:
‘The geomagnetic field has been decaying for the last 3,000 years,’ said Dr Nicolas Thouveny from the European Centre for Research and Teaching of Environmental Geosciences (CEREGE) in Aix-en-Provence, France. ‘If it continues to fall down at this rate, in less than one millennium we will be in a critical (period).’ Dr Thouveny is one of the principal investigators on the five-year EDIFICE project, which has been running since 2014. Dr Thouveny and his team looked at two particular forms of elements that allowed them to probe the history of our planet’s magnetic field in greater detail.
When this happens, these cosmic rays collide with more and more atoms in our atmosphere, such as nitrogen and oxygen. This produces variants of elements called cosmogenic isotopes, such as carbon-14 and beryllium-10, which fall to the surface. And by studying the quantities of these in cores, we can see when polarity reversals took place.
Polarity reversals give warning signs: the magnetic field weakens by about 90% to a threshold level. This
process can take thousands of years, and during this time, the lack of a protective magnetic shield around our planet allows more cosmic rays reach earth's
surface - and the organisms, like us, living there. to hit us. As the field ebbs and recovers its strength; it allows cosmic rays to penetrate. The last excursion occurred 40,000 years ago,
and evidence suggests we are heading in that direction again.
‘The geomagnetic field has been losing 30 percent of its intensity in the last 3,000 years,’ said Dr Thouveny. ‘From this value, we predict it will drop to near zero in a few centuries or a millennia.’
However, the USGS poo-poo's the idea, saying:
Are we about to have a magnetic reversal? Almost certainly not. Since the invention of the magnetometer in the 1830s, the average intensity of the magnetic field at the Earth's surface has decreased by about ten percent. We know from paleomagnetic records that the intensity of the magnetic field decreases by as much as ninety percent at the Earth's surface during a reversal. But those same paleomagnetic records also show that the field intensity can vary significantly without resulting in a reversal. So a reduced intensity in the magnetic field does not necessarily mean that a reversal is about to occur. Moreover, the decrease in intensity is not a dramatic departure from normal. For all we know, the field may actually get stronger at some point in the not-so-distant future. Predicting the occurrence of a reversal based on the current state of the magnetic field is extremely difficult. Reversals are not instantaneous--they take place over a period of hundreds to thousands of years. We wouldn’t know that a reversal is happening until it was half over.
Yes, the same government that now admits lying to the American public about the existence of UFO's for the past 70 years, tells you not to worry.
This is the big unknown. Most scientists say they do not think a reversal of magnetic poles would have a large impact upon life on earth. But no one was there to see when it happened in the past, and the technologies, satellites, power grids, cell phones and computers did not exist during the last reversal, so it's really anyone's guess at this point.
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