Geochemists at Rensselaer Polytechnic Institute are challenging commonly held ideas about how gases are expelled from the Earth.
Their theory could change the way scientists view the formation of Earth’s atmosphere and those of our distant neighbors, Mars and Venus, throwing into doubt the timing and mechanism of atmospheric formation on terrestrial planets.
Lead by E. Bruce Watson, Institute Professor of Science at Rensselaer, the team has found strong evidence that argon atoms are tenaciously bound in the minerals of Earth’s mantle and move through these minerals at a much slower rate than previously thought. In fact, they found that even volcanic activity is unlikely to dislodge argon atoms from their resting places within the mantle. This is in direct contrast to widely held theories on how gases moved through early Earth to form our atmosphere and oceans, according to Watson.
Scientists believe that shortly after Earth was formed, it had a glowing surface of molten rock extending down hundreds of miles. As that surface cooled, a rigid crust was produced near the surface and solidified slowly downward to complete the now-solid planet. Some scientists have suggested that Earth lost all of its initial gases, either during the molten stage or as a consequence of a massive collision, and that the catastrophically expelled gases formed our early atmosphere and oceans. Others contend that this early “degassing” was incomplete, and that primordial gases still remain sequestered at great depth to this day. Watson’s new results support this latter theory.
“For the ‘deep-sequestration’ theory to be correct, certain gases would have to avoid escape to the atmosphere in the face of mantle convection and volcanism,” Watson said. “Our data suggest that argon does indeed stay trapped in the mantle even at extremely high temperatures, making it difficult for the Earth to continuously purge itself of argon produced by radioactive decay of potassium.”
‘E. Bruce Watson’ photo by RPI/Kris Qua