Dutch scientists have reported that our planet's magnetic field is becoming gradually less stable.
"On average, there is a reversal around every 400,000 years, but this varies a lot." The geological record suggests that the last reversal was around 800,000 years ago.
Furthermore, there is already evidence to show that the field has been weakening over the last few centuries – some archaeological remains suggest that the field was far stronger in the time of the Roman Empire, some 2,000 years ago.
They say the
next reversal could happen in the next few centuries, or it could be a million years away. But they are sure that the process takes thousands of years to complete. I would respectfully suggest that their measurements of the prior reversals are not accurate enough to tell if it happened more suddenly (like, in a day).
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Meanwhile, a Cardiff team says that when we pass through the galactic plane every 35 to 40 million years, the chances of a
comet collision are increased tenfold. And, without saying what scale of soon they are talking about, state:
And in case you're interested in when the next comet infestation might occur, our present position in the galaxy suggests we are now very close to another such period.