During an excursion or a reversal, the magnetic field is considerably weakened and allows many more cosmic rays to reach the surface of the planet.
These energetic particles from space can be damaging to life on Earth if too many reach the surface. And he suggests that Thouveny and his colleagues fail to properly take the period before the reversal into account.
Jonathan O'Callaghan is a freelance journalist covering commercial spaceflight, space exploration and astrophysics. Follow Jonathan O'Callaghan on Twitter. Already a subscriber? 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, years and it is nearly , 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 years hence. We have no complete record of the history of any reversal, so any claims we can make are mostly on the basis of mathematical models of the field behaviour and partly on limited evidence from rocks that retain an imprint of the ancient magnetic field present when they were formed.
For example, the mathematical simulations seem to suggest that a full reversal may take about one to several thousand years to complete. This is fast by geological standards but slow on a human time scale. As above, we have limited evidence from geological measurements about the patterns of change in the magnetic field during a reversal. We might expect to see, based on models of the field run on supercomputers, a far more complicated field pattern at the Earth's surface, with perhaps more than one North and South pole at any given time.
We might also see the poles 'wandering' with time from their current positions towards and across the equator. The overall strength of the field, anywhere on the Earth, may be no more than a tenth of its strength now. 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. At the Earth's surface, the atmosphere acts as an extra blanket to stop all but the most energetic of the solar and galactic radiation.
In the absence of a magnetic field, the atmosphere would still stop most of the radiation. Indeed the atmosphere shields us from high-energy radiation as effectively as a concrete layer some 13 feet thick. 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. The source of the magnetic field is the iron-rich liquid outer core of the Earth. Without it, intense cosmic and solar radiation will fry circuit boards and increase the risk of cancer in astronauts.
Our modern way of life could cease to exist. We know this because we're already seeing a glimpse of this in an area called the South Atlantic Anomaly. Turns out, the direction of a portion of the magnetic field deep beneath this area has already flipped! And scientists say that's one reason why the field has been steadily weakening since As a result, the Hubble Space Telescope and other satellites often shut down their sensitive electronics as they pass over the area. And astronauts on the International Space Station reported seeing a higher number of bright flashes of light in their vision, thought to be caused by high-energy cosmic rays that the weaker field can't hold back.
Since experts started measuring the Anomaly a few decades ago, it has grown in size and now covers a fifth This is so extreme that it could be a sign we're on the brink of a polar flip, or we may already be in the midst of one! Mitchell: They don't know. The last time the poles reversed was , years ago so it's not like we have a record for this. Mitchell: In the past 65 million years since the last mass extinction there have been reversals roughly every , years.
So what gives? 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.
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