This paper
Deep-sea sediment records of the Laschamp geomagnetic field excursion (∼41,000 calendar years before present)
concludes that the narrow Laschamps excursion event, or class I
excursions in general, are more closely related to normal secular
variation and are not necessarily a prelude to magnetic field reversal.
So what are they and what causes them? The geomagnetic field suffered
for some time and so one would imagine that life did as well: "magnetic
field intensities less than 10% of normal that persisted for almost 2000
years". How relevant is this event to the megafaunal extinctions for
example?
Wikipedia Geomagnetic Excursions
Wikipedia Earth's Magnetic Field
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