New study sheds light on the composition of the Earth’s earliest atmosphere.
Understanding the atmospheric and surface conditions of early Earth, especially before life originated, is crucial to comprehend Earth’s ability to support life. The atmosphere of terrestial planets is believed to have been created by the release of volatile substances from the planet’s interior and its composition is mainly controlled by the oxidation state of the mantle.
To understand the mantle oxidation state, the abundance of ferrous (Fe2+) and ferric (Fe3+) iron in the mantle are key because the mantle oxidation state varies with the relative abundance of these two iron oxides.
Ehime University has led an experimental study showing that the formation efficiency of Fe3+ via redox disproportionation of Fe2+ in metal-saturated magma under high pressures corresponding to the depth of the lower mantle is higher than previously thought. In this reaction, Fe3+ and metallic iron (Fe0) are formed from 2Fe2+, and the segregation of Fe0 into the core increases the content of Fe3+ in the residual magma and its oxidation state.
The experimental results indicate that the Fe3+ content of the Earth’s magma ocean during core formation was about one order of magnitude higher than the present upper mantle. This suggests that the magma ocean was much more oxidizing than the present Earth’s mantle after the core formation, and the atmosphere formed by the degassing of volatiles from such a highly oxidizing magma would have been rich in CO2 and SO2.
In addition, the authors found that the estimated oxidation state of the Earth’s magma ocean can explain that of Hadean magmas of more than 4 billion years ago by inference from geological records.
Because the formation efficiency of biomolecules in a CO2-rich atmosphere is quite low, the authors speculated that the late accretion of reducing materials after the formation of the Earth played an important role in supplying biologically available organic molecules and the formation of a habitable environment.
Reference: “Hadean mantle oxidation inferred from melting of peridotite under lower-mantle conditions” by Hideharu Kuwahara, Ryoichi Nakada, Shintaro Kadoya, Takashi Yoshino and Tetsuo Irifune, 4 May 2023, Nature Geoscience.
The study was funded by the Japan Society for the Promotion of Science.
Utafiti mpya unafunua jinsi angahewa la kwanza la Dunia lilivyotengenezwa. Kuelewa hali ya anga na uso wa Dunia ya mapema, hasa kabla ya uhai kutokea, ni muhimu kuelewa uwezo wa Dunia kuunga mkono uhai. Anadhaniwa kuwa angahewa la sayari za dunia ziliundwa na kutolewa kwa vitu vya kuteleza kutoka ndani ya sayari na muundo wake unadhibitiwa hasa na hali ya oksidi ya mantle. Ili kuelewa hali ya oksijeni ya mantle, wingi wa chuma (Fe2+) na chuma (Fe3+) katika mantle ni muhimu kwa sababu hali ya oksijeni ya mantle inatofautiana na wingi wa kiasi cha oksidi hizi mbili za chuma. Chuo Kikuu cha Ehime kimesababisha utafiti wa majaribio unaoonyesha kuwa ufanisi wa malezi ya Fe3+ kupitia disproportionation ya redox ya Fe2+ katika magma yenye chuma chini ya shinikizo la juu linalofanana na kina cha mantle ya chini ni kubwa kuliko ilivyodhaniwa hapo awali. Katika mmenyuko huu, Fe3+ na chuma chuma (Fe0) hutengenezwa kutoka Fe2+ na kutenganishwa kwa Fe0 katika kiini huongeza maudhui ya Fe3+ katika magma iliyobaki na hali yake ya oksidi. Matokeo ya majaribio yanaonyesha kwamba Fe3+ yaliyomo katika bahari ya magma ya Dunia wakati wa kuundwa kwa kiini ilikuwa karibu na kiwango kimoja cha ukubwa zaidi kuliko mantle ya juu ya sasa. Kwa hivyo, bahari ya magma ilikuwa na oksijeni nyingi kuliko mantle ya Dunia ya sasa baada ya malezi ya msingi, na anga iliyoundwa na desgasification ya vimelea kutoka magma yenye oksijeni ya juu ingekuwa na CO2 na SO2. Kwa kuongezea, watafiti walipata kuwa hali ya oksijeni ya bahari ya magma ya Dunia inaweza kuelezea ile ya magma ya Hadean ya zaidi ya miaka bilioni 4 iliyopita kwa inference kutoka kwa rekodi za kijiolojia. Kwa sababu ufanisi wa malezi ya biomolecules katika anga yenye CO2 ni chini sana, waandishi walidhani kwamba kuongezeka kwa vifaa vya kupunguza baada ya kuundwa kwa Dunia ilicheza jukumu muhimu katika usambazaji wa molekuli za kikaboni zinazopatikana na kuunda mazingira ya kuishi. "Hideyoshi Kobayashi, Ryoichi Nakada, Shintaro Kobayashi, Takashi Yoshino na Tetsuo Ifufu, 4 Mei 2023, ""Uchunguzi wa Peridotite chini ya hali ya chini ya mantle.""" Utafiti huo ulifadhiliwa na Shirika la Japan la Kukuza Sayansi.