Submitted by somethingX t3_122dugg in askscience
mcnessa32 t1_jdruaz1 wrote
Reply to comment by wazoheat in Around 550 million years ago the earth's magnetic field almost collapsed, but then strengthened a few million years later. Scientists say this may have been due to the formation of the inner core. But why exactly would that cause the magnetic field to get stronger? by somethingX
What impact would a near collapse of the magnetic field have on the planet? Does 550M years ago coincide with any known extinction periods?
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.
PolymerPolitics t1_jdsa9ji wrote
All life would have been aquatic then. Water can effectively shield radiation.
ronflair t1_jdscqhs wrote
Depends on the depth. According to this site, a water layer 7cm thick reduces ionizing radiation dosage by about half.
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.
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.
ronflair t1_jdskzk1 wrote
You still would get a net increase in surface ionizing radiation, which would increase as a positive feedback loop the longer the magnetosphere was “off”.
According to NASA, a prolonged loss of the magnetosphere could erode the protective layers of the atmosphere. More cosmic rays would reach the surface as well.
https://science.nasa.gov/science-news/news-articles/earths-magnetosphere
zanderkerbal t1_jdsdja8 wrote
Is that last bit an established theory, or your own speculation?
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.
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.
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
mcnessa32 t1_jds8139 wrote
Thank you!
[deleted] t1_jdrvwv0 wrote
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