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Suchnamebro t1_jdr0s6z wrote

How can they even find out what happened 550 million years ago?

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wazoheat t1_jdra4eq wrote

Specifically for Earth's magnetic field, when rock with magnetic materials is formed it retains magnetism from its environment, giving us information about the strength and direction of the geomagnetic field at the time the rock formed. So if you find certain rocks of a certain age you can use them to get information about Earth's magnetic field at the time.

For volcanic rock, this is because molten rock is too hot to be magnetic. As it solidifies and cools below a certain critical temperature (its Curie temperature), any magnetic minerals will retain the magnetic field of their environment, and so these rocks preserve information about the strength and direction of the geomagnetic field when they formed. This is the same principle by which bar magnets are created.

There are also several ways that sedimentary rocks can end up with a "fossil" magnetic field. The study of these phenomena is called paleomagnetism.

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mcnessa32 t1_jdruaz1 wrote

What impact would a near collapse of the magnetic field have on the planet? Does 550M years ago coincide with any known extinction periods?

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ronflair t1_jds7p7s wrote

On the contrary, coincidentally it corresponds with the Cambrian Explosion, when all multicellular organisms and phyla arose. Before that, for billions of years, everything was mainly unicellular, such as cyanobacteria; afterwards, dinosaurs, trees, mammals, humans etc.

https://en.m.wikipedia.org/wiki/Cambrian_explosion

Could a severely weakened magnetic field have lead to a massive increase in mutagenesis globally, essentially jumpstarting a new evolutionary arms race? Maybe. We do use radiation and other mutagens to do just that in the laboratory.

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PolymerPolitics t1_jdsa9ji wrote

All life would have been aquatic then. Water can effectively shield radiation.

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ronflair t1_jdscqhs wrote

Depends on the depth. According to this site, a water layer 7cm thick reduces ionizing radiation dosage by about half.

https://space.stackexchange.com/questions/1336/what-thickness-depth-of-water-would-be-required-to-provide-radiation-shielding-i

If correct, means that cyanobacterial mats inhabiting the top layers of oceans will still be receiving significantly more ionizing radiation than normal. We’re not talking about enough radiation to sterilize the planet, just enough to significantly increase the rate of mutagenesis.

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Octavus t1_jdsj58i wrote

You are forgetting that the atmosphere is responsible for the bulk of Earth's radiation shielding and is equal to about 10 meters of water.

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zanderkerbal t1_jdsdja8 wrote

Is that last bit an established theory, or your own speculation?

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ronflair t1_jdsiy99 wrote

As a molecular biologist, It just seemed like an obvious connection to me given the time frame. I have not googled the hypothesis but if geologists have noted years ago that the magnetic field was severely weakened during that geologic era, I would be surprised if no evolutionary biologist noted the connection. That said, I don’t see that mentioned as a hypothesis for the Cambrian explosion on wikipedia.

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FlattopMaker t1_jdt9cmi wrote

The magnetic field both causes and impacts the rate and most development as evidenced by magnetosomes in the fossil record and organisms today. Some species exhibit greater function in hypomagnetic conditions, and may have evolutionary impact when combined with known mutagenic effects of radiation exposure. We don't have known mechanism of action identified yet for the HMF (hypomagnetic field) theory and observations. Link to a review of speculations about causes and effects relating the magnetic field to the Cambrian explosion.

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TrumpetOfDeath t1_jdu888e wrote

I’ve heard this theory before, but there’s no real evidence to support it besides it being a coincidence.

As mentioned elsewhere, life was aquatic back then and water is a pretty good radiation shield. Even most planktonic algae are mixed throughout the surface layer, which can be hundreds of meters deep, they don’t float at the surface for long

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noirxgrace t1_jdu9ilh wrote

I remember reading about the same. Since lava's temperature is well above above the Curie temperature of magnetite(800^(o)C), and it cools down, the orientation of the magnetite particles are all aligned and proportional to the ambient magnetic field, which makes it ferromagnetic.

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