# Earth shaped by primordial H$_2$ atmospheres

**Authors:** Edward D. Young, Anat Shahar, Hilke E. Schlichting  
**arXiv:** [2304.07845](https://arxiv.org/abs/2304.07845)  
**Date:** 2023-04-16  
**Summary page:** https://www.summarizepaper.com/en/paper/2304.07845v1/

## Key points

- Earth's water, intrinsic oxidation state, and metal core density can be attributed to the equilibrium between H$_2$-rich primary atmospheres and underlying magma oceans in its progenitor planetary embryos.
- Earth's fundamental chemical features can be explained by reactions between hydrogen-rich atmospheres and magma oceans during planet formation.
- Rocky exoplanets commonly formed with hydrogen-rich envelopes that were lost over time, leading to the hypothesis that Earth may have also formed from bodies with H$_2$-rich primary atmospheres.
- Water is produced from dry starting materials resembling enstatite chondrites as oxygen from magma oceans reacts with hydrogen.
- Hydrogen derived from the atmosphere enters the magma ocean and eventually the metal core at equilibrium, causing metal density deficits matching that of Earth.
- Oxidation of the silicate rocks from solar-like to Earth-like oxygen fugacities also ensues as Si, along with H and O, alloys with Fe in the cores.
- This study provides a simple explanation for fundamental features of Earth's geochemistry which is consistent with rocky planet formation across the galaxy.

## Summary

In a recent study published in Nature, Edward D. Young, Anat Shahar, and Hilke E. Schlichting propose that Earth's water, intrinsic oxidation state, and metal core density can be attributed to the equilibrium between H$_2$-rich primary atmospheres and underlying magma oceans in its progenitor planetary embryos. The authors use a self-consistent thermodynamic model to demonstrate that Earth's fundamental chemical features can be explained by reactions between hydrogen-rich atmospheres and magma oceans during planet formation. The study draws on findings from exoplanet research which suggest that rocky exoplanets commonly formed with hydrogen-rich envelopes that were lost over time. This led the authors to hypothesize that Earth may have also formed from bodies with H$_2$-rich primary atmospheres. The authors explain that water is produced from dry starting materials resembling enstatite chondrites as oxygen from magma oceans reacts with hydrogen. Hydrogen derived from the atmosphere enters the magma ocean and eventually the metal core at equilibrium, causing metal density deficits matching that of Earth. Oxidation of the silicate rocks from solar-like to Earth-like oxygen fugacities also ensues as Si, along with H and O, alloys with Fe in the cores. Overall, this study provides a simple explanation for fundamental features of Earth's geochemistry which is consistent with rocky planet formation across the galaxy. By understanding how these chemical traits arise during planet formation processes we can gain insight into how other planets may have formed in our universe.