Science Forums 2

[CraigD]

Originally Posted by Thunderbird

These dynamics allows for the formation of a mobile core, that envelops the planet in a protective electromagnetic shield, and not to mention the mobility of plate tectonics. Intuitively It strikes me that without these underling dynamics the planet could not sustain the dynamics of a life support system.

One might think that Earth’s magnetic field provides an important shield for its life, primarily against solar wind protons. Solar wind protons have about the same energy (1 keV), and have about the same effect of biological organisms - ionization, which can break chemical bonds in tissue, causing injury and death, or in genetic material, causing cancer and mutation – as soft x-rays.

One would, I’m pretty sure, be entirely wrong.

There’s a lot of evidence and reason to suggest that the absence of a magnetic field, while it might change the nature of life on Earth, causing different species to thrive, would not prevent it from having formed. A couple key ones come to mind

• The Earth’s ionosphere is also an effective charged particle shield, so even if it had no magnetic field, its wouldn’t get dramatically more radiation than it does.*
• Geomagnetic reversals. Geological evidence strongly suggest that the Earth’s magnetic field swaps polarity every million years of so (and sometimes much more frequently), with centuries or longer periods in which the field strength is nearly zero. Yet it appears these events did not cause mass extinctions, or otherwise much disrupt the ecosystem.
• Radiation extremophiles. Even if the preceding effects and evidence were absent, many organism, some surprising large and complex, have been discovered that thrive under sustained high doses of ionizing radiation. As the saying goes (well, OK, the saying appears to be from a 1993 Michael Crichton screenplay, but it’s a good one, IMHO, anyway ) “life, uh … finds a way.”

Models and probe data indicate that Mars no longer has a significant magnetic field, and a much thinner atmosphere than Earth (in large part, it’s believed, due to being stripped away by exposure to the solar wind), but it’s know to have an ionosphere, so its surface is effectively shielded from the particles that a magnetic field would also shield it from.

So it’s not so much that Martian life – if it exists – suffers from the lack of enough magnetic field, but from the lack of enough atmosphere. Models and probe data suggest that Mars once had a significant magnetic field and a thicker atmosphere, but lost both about 4 billion years ago. Whether Mars has ever had life, or still has some extremophile survivors, science has yet to compellingly reveal.
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* Calculating from data (Apollo 11 Solar Wind Composition Experiment and THE SOLAR X-RAY FLARE OF 7 JULY 1966,) on the observed solar wind and x-ray fluxes, we get then that the Earth’s magnetic field reduces its influx of a fairly narrow range of ionizing (1 keV, in the soft x-ray band) radiation by a large factor of about 100,000. The solar output is very variable, with infrequent burst of a few minutes of as much as 10,000 times the usual x-rays, so Earth without its magnetic field and atmosphere would be have about 10 times the x-ray band ionizing radiation as – bad news for the majority of surface-dwellers (though not as bad news as the lack of atmosphere :yikes: ).

Fortunately, Earth has an atmosphere, with an ionosphere that’s also an effective charged particle shield, so even if it had no magnetic field, its surface wouldn’t be awash in solar wind protons.