Outer space is not a particularly friendly place. One of its hazards is cosmic rays, which are elementary particles—electrons, protons, helium nuclei, and heavier nuclei—traveling at velocities approaching the speed of light. They come from many sources, including the sun and cosmic rays from distant supernovae, the explosions of stars. These catastrophic events send great numbers of particles hurtling through space.
In The Search for Life in the Universe, D. Goldsmith and T. Owen speculate that without some sort of protection, life on Earth's surface would be extinguished within several generations by cosmic rays hitting our planet's surface. However, the vast majority of cosmic rays are deflected by Earth's magnetic field. The innermost layer of our planet, its core, is made up mainly of iron, which in the outermost region of the core is in a liquid state. As Earth spins, it creates convective movement in this liquid that produces a giant magnetic field surrounding the entire planet. What produces the convection cells in the core is loss of heat. Heat must be exported out of the core, and this liberation of heat appears to be greatly influenced by Earth's plate tectonic regime. Joseph Kirschvink of Cal Tech has suggested that without plate tectonics, there would not be enough temperature difference across the core region to produce the convective cells necessary to generate Earth's magnetic field; no plate tectonics, no magnetic field. The magnetic field also reduces "sputtering" of the atmosphere, a process whereby the atmosphere is gradually lost into space. No magnetic field, perhaps no animal life. Plate tectonics to the rescue again.
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