Massive Impact-Induced Release of Carbon and Sulfur Gases in the Early Earth's Atmosphere

Atmospheric and surface conditions during the first billion years of Earth's history are poorly understood due to the paucity of geological and geochemical constraints. Early atmospheric models indicate that the Earth could have been in a frozen state for hundreds of millions of years due to the reduced luminosity of the young Sun, which was approximately 20-30% less intense than today at visible wavelengths. However, the oldest terrestrial zircons dating back to 4.3-4.4 Gyr ago hint at protoliths that interacted with liquid water at or near the surface of the Earth based on deviation of stable oxygen isotope ratios (δ18O) from mantle values. Recent developments in scientific understanding of the collisional history of the Hadean and early-Archean Earth indicate that large collisions may have been a fundamental geophysical process. In addition to altering the near surface environment by excavation and melting of large volumes of terrestrial rocks, these energetic events may also have resulted in massive release of volatiles to the primordial atmosphere. In this work we show that the early bombardment flux of large impactors ( >100 km) facilitated the atmospheric release of greenhouse gases from Earth's mantle. The picture emerging is one in which after the transient havoc of hot, silicate-rich atmospheres has passed, impact-generated melt outgassing could have substantially altered surface conditions. Release of greenhouse gases such as CO2 may have been sufficient to temporarily offset weaker insolation from the faint young Sun. Depending on the timescale for atmospheric CO2 drawdown, impact-induced outgassing could have sustained clement surface conditions episodically (1-10 Myr) or for a protracted time (100s of Myr). The bombardment also delivered and redistributed to the surface large quantities of sulfur, one of the most important elements for life. The stochastic occurrence of large collisions could provide insights on why the Earth and Venus, considered Earth's twin planet, exhibit radically different atmospheres.