Does Earth's mantle hold the key to keeping our planet hospitable for life?

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SUMMARY

The Earth's mantle contains significant amounts of oxygen stored in the mineral majorite, which plays a crucial role in maintaining the planet's habitability. Majorite, a garnet variant, is found in the upper mantle, which consists of 60% olivine, 18% orthopyroxene, 12% garnet (including majorite), and 10% clinopyroxene. A study published in the journal Nature on September 27 highlights that without this oxygen reservoir, Earth could resemble the barren conditions of Mars. The discussion also touches on the relationship between majorite and the geological water cycle, noting its phase transition to perovskite in the lower mantle.

PREREQUISITES
  • Understanding of mineralogy, specifically garnet types like majorite and akimotoite.
  • Knowledge of Earth's mantle composition, including olivine and pyroxene minerals.
  • Familiarity with geological processes, particularly phase transitions under pressure and temperature.
  • Awareness of the water cycle in geological contexts, including the role of subducting slabs.
NEXT STEPS
  • Research the properties and formation conditions of majorite and its significance in the mantle.
  • Explore the geological implications of the upper mantle's composition on Earth's habitability.
  • Study the phase transition of majorite to perovskite and its effects on mantle dynamics.
  • Investigate the role of hydrous volatiles in the transition zone and their impact on the geological water cycle.
USEFUL FOR

Geologists, mineralogists, and researchers interested in Earth's mantle dynamics, habitability studies, and the geological water cycle will benefit from this discussion.

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http://news.yahoo.com/s/livescience/20071002/sc_livescience/hugestockpileofoxygenfounddeepinsideearth;_ylt=AlP5Y3bcO_CrB7jCXyUGvUkPLBIF

A mineral that acts like a sponge beneath Earth's surface stores more oxygen than expected, keeping our planet from becoming dry and inhospitable like Mars.



The key to the abundant oxygen storage is the mineral majorite, which exists deep below Earth's surface in the mantle. Without the oxygen stockpile, Earth would probably be a barren planet hostile to life, authors of a study suggest in the Sept. 27 issue of the journal Nature.
 
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Yes, oxygen is abundant in the mantle, take the upper mantle, composed of 60% olivine (Mg, Fe)2SiO4, 18% orthopyroxene (Mg, Fe) SiO3, 12% garnet (e.g. majorite) (Ca, Mg, Fe)3Al2Si3O12, with about 10% clinopyroxene Ca(Mg, Fe)Si2O6. There is a lot of oxygen there. Interesting that they pick out majorite, which I believe (from memory) forms under transition zone conditions - it's probably the most dominant type of garnet along with akimotoite - I'd like to know more about the significance of that. With regards to the water forming hypothesis, I was under the impression that hydrous volatiles were present in the transition zone, perhaps so much so that the rocks there were oversaturated, leading to partial melt (e.g. Bercovici and Kerato). So I would hesitate to accept that the "decomposition" of majorite was releasing oxygen which went on to join with hydrogen to form water. There already seems to be a lot of water in the upper mantle much of which can be accounted for by subducting slabs bringing it down with them. Majorite cannot exist in the lower mantle, it undergoes a phase transition into perovskite under the increased pressure and temperature. So if anything, majorite is just a weird stop gap in the geological water cycle in a very abstract way.
 
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