The sands that built this region were laid down in what was once a warm, shallow sea, with magnetic minerals trapped in place as sediments drifted to the quiet ocean floor and compacted to form new rock layers. Gallet and his colleagues first visited the site in the early s, collecting around samples from the nearly vertical face of rock. This work revealed a period during the Middle Cambrian that saw at least six to eight field reversals every million years.
The fast rate left him and his colleagues with a nagging suspicion that they needed to collect more samples.
In the summer of , they returned to do just that, cutting some small blocks of rock every four to eight inches. Analysis of the magnetic signatures confirmed their suspicion: Over the three million years captured in their samples, they detected a striking 78 field reversals. And 22 of the samples record only one reversal, he notes, hinting that perhaps the true rate is even higher. For now, the new study offers more questions than answers.
While many studies suggest this likely began or million years ago, perhaps the intense flipping in the Middle Cambrian came from a late period of inner core formation. The only other time period with comparably high reversals, known as the Ediacaran, occurred some to million years ago, a time that intriguingly lines up with a mass die-off of life, Meert notes.
Studies suggest that the flip-flopping magnetic field of the Ediacaran was extremely weak, which might have exposed early life on Earth to punishing surface conditions. Read more about the otherworldly critters of the Ediacaran.
But no mass extinction coincides with the newly proposed hyperactive flipping in the Middle Cambrian, when life was blooming in a myriad of forms.
Maybe evolution gave those creatures a helping hand, he suggests, resulting in the burst of burrowers and other animals who could seek shelter from harmful solar rays. One curious pattern is that there seems to be some cyclicality to the changes, with prolonged periods without flips happening roughly every million years. Between these delays, the field seems to flip at a rate as fast as five times every million years, and these periods are then punctuated with hyperactive spurts.
And even if a reversal is on the horizon, each one happens in slow motion from our perspective, with the poles shifting places over several thousand years. One big challenge with deciphering these patterns is that the record remains spotty. Rocks this ancient usually get squashed and transformed as the continents collide, obscuring many ancient records, explains Van der Boon, who studies much more sparse rock records that show a potential period of elevated flipping around million years ago.
While the researchers did the best they could in challenging conditions, this result still needs verification from other parts of the globe to confirm it was truly a planet-wide affair, says Florian Lhuillier , a geomagnetist at Ludwig Maximilian University of Munich. The minerals in these rocks can similarly record the magnetic field as lava cools to become stone. Larmor suggested in that a self-exciting dynamo could explain the magnetic field of the earth, as well as that of the sun and other stars, but it was Elsasser and Bullard in the s who showed how motion in the liquid core of the earth might produce a self-sustaining magnetic field.
By this time seismology and other studies had given a clearer picture of the earth, as having a solid inner core, a liquid outer core, both with a composition more of metal mainly iron than rock, and a rocky mantle, all below a thin crust that is all we can directly see. Energy from radioactivity travels outwards as heat, producing thermal convection in the core.
It seems that this convection is the cause of the earth's magnetic field, although our knowledge of the core and its dynamics is sketchy. The earth's dynamo is unstable, as is shown by magnetic reversals, when the polarity of the whole magnetic field changes over. These have been a continuing feature of the earths history, with the last about , years ago. In fact, some magnetic field changes seen at the earth's surface with a timescale of a year or two magnetic jerks may be produced by changes in the dynamo, although this is still being argued.
The importance of this is that we cannot exactly predict magnetic values. We can describe the current field, from observatory and satellite measurements, and how it has changed from the previous field, which is calculated internationally on a 5-year basis, but in perhaps 5 or 10 years there may be changes which we can't foresee. A recent study has suggested that the Devonian-Carboniferous mass extinction is linked to elevated UV-B levels, around the same as the weakest field measurements from the MPDL.
Liverpool palaeomagnetist and lead author of the paper, Dr. Hawkins, J. Michael Grappone, Courtney J. Sprain, Patipan Saengduean, Edward J. DOI: Cosmic rays are deflected less when the field is weak, and collide directly with ozone, stripping it away. Ozone absorbs UV-B and serves as the primary protection layer.
Will we still be here when the mag fields are low, poles flip, etc and how will it all affect our electronics? Which are, as of today, Life itself?
If fusion becomes a reality? What balls? What an ignorant comment Karen..
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