[victor106]

TIL From the article “To determine the age of the tools, the researchers took advantage of the planet’s changing magnetic field.

From time to time, Earth’s magnetic field flips, turning north to south. Magnetic minerals in the soil and ocean are pushed into alignment with the field; when they are trapped in rocks, they still point in the telltale direction.

Geophysicists have precisely determined the timing of these magnetic flips, which have taken place at the same time all around the world. It’s a useful way to date the material found in layers of rock.”

[njarboe]

These flips happen quickly on a geologic timescale but are not quick on a human timescale. It takes around 1-10 thousand years for the field to flip. The last one happened around 780k years ago. More often the magnetic field gets quite weak for awhile, like the field is going to flip, but then the magnetic field returns to the same strength and direction. These are called excursions and the last one of these was likely the Laschamp excursion about 40k years ago.

[ericd]

Huh, interesting. Do you know if anyone has looked at whether the rate of genetic mutations increases during those 10k year periods of weakened magnetic field? Seems like that would cause the magnetosphere to become less effective at deflecting cosmic radiation.

[njarboe]

Many people have looked into if these reversals can cause extinction events and they don't appear to. Determining a change in average mutation rates seems like something that would not be possible from the rock record. The last reversal was so long ago that DNA does not survive well enough to do a good study even if one had the right kind of samples to work with.

[ericd]

Yeah, makes sense. I was thinking that you could look for an uptick in biodiversity or something from the fossil record, but I'm sure it would be tricky to separate the reasons for that.

[Pica_soO]

Super interesting, thanks for posting about the Laschamp Event

[hyperpallium]

Funfact: key evidence for the theory of tectonic plates was the changing magnetic field direction in rocks with distance from their magma source.

Always seemed like one fantastical theory being supported by another fantastical theory. (Don't worry, I'm not a tectonic skeptic.)