Prebiotic chemistry and atmospheric warming of early Earth by an active young Sun

Abstract

Nitrogen is a critical ingredient of complex biological molecules 1. Molecular nitrogen, however, which was outgassed into the Earth's early atmosphere 2 , is relatively chemically inert and nitrogen fixation into more chemically reactive compounds requires high temperatures. Possible mechanisms of nitrogen fixation include lightning, atmospheric shock heating by meteorites, and solar ultraviolet radiation 3,4. Here we show that nitrogen fixation in the early terrestrial atmosphere can be explained by frequent and powerful coronal mass ejection events from the young Sun-so-called superflares. Using magnetohydrodynamic simulations constrained by Kepler Space Telescope observations, we find that successive superflare ejections produce shocks that accelerate energetic particles, which would have compressed the early Earth's magnetosphere. The resulting extended polar cap openings provide pathways for energetic particles to penetrate into the atmosphere and, according to our atmospheric chemistry simulations, initiate reactions converting molecular nitrogen, carbon dioxide and methane to the potent greenhouse gas nitrous oxide as well as hydrogen cyanide, an essential compound for life. Furthermore, the destruction of N 2 , CO 2 and CH 4 suggests that these greenhouse gases cannot explain the stability of liquid water on the early Earth. Instead, we propose that the e cient formation of nitrous oxide could explain a warm early Earth. Here we develop a new concept for the rise of prebiotic chemistry on early Earth that suggests abiotic nitrogen fixation mediated by the energy flux from palaeo-solar eruptive events. The flare statistics of Kepler data suggest that the frequency of occurrence of superflares with energies >5 × 10 34 erg observed on G-type dwarfs follows a power-law distribution with a spectral index between α = −2.0 and −2.3, which is comparable to those observed on active M-type red-dwarf stars and the Sun 5,6. If the occurrence rate of superflares on young solar-like stars is ∼0.1 events per day 6 , then the frequency of super Carrington-type flare events with energy

Coronal mass ejections and their sheath regions in interplanetary space

“…The successive super-eruptions may have also affected significantly the atmosphere of the Earth. Simulations constrained by the Kepler Space Telescope observations suggest that the magnetospheric compression by ICMEs allowed energetic particles to penetrate deep into the atmosphere, affecting pre-biotic chemistry and atmospheric warming of the early Earth (Airapetian et al 2016) .…”

The Propitious Role of Solar Energetic Particles in the Origin of Life

“…The input spectrum at the top of the atmosphere is adopted from the energetic January 2005 SEP event, and corresponds to an energy flux (per unit energy) of 5 × 10 11 pr cm −2 MeV −1 at 0.1 MeV, while the associated spectral index is −2.15 (Mewaldt et al 2012). We note that the 2005 SEP event has been studied previously as a representative example of a high-fluence solar proton event (associated with an X7 solar flare) in the context of prebiotic chemistry (Airapetian et al 2016). SEP events with total fluences greater than the January 2005 event have been documented (Mewaldt 2006), and hence it might constitute a representative example for the active young Sun.…”

“…However, we caution that the young Sun was not necessarily characterized by statistics similar to active solar-type stars studied by the Kepler mission. With this caveat in mind, we use the above value to conclude that the frequency N 0 of Carrington-type events for the ancient young Sun may have been N 0 40 per day, which is lower by a factor of ∼ 6 compared to Airapetian et al (2016); these events are less powerful than superflares but occur more frequently with adequate energy release. Although large flares are often accompanied by CMEs and SEPs (Emslie et al 2012;Reames 2013;Desai & Giacalone 2016), not every such event will impact the planet.…”

“…The dangers posed by SEPs are especially significant since they may cause significant ozone depletion and biological damage (Dartnell 2011;Melott & Thomas 2011;Lingam & Loeb 2017a). However, recent evidence intriguingly suggests that flares could have played a beneficial role in the origin of life (abiogenesis) by delivering the requisite energy for the prebiotic synthesis of organic compounds (Buccino et al 2007;Airapetian et al 2016;Nava-Sedeño et al 2016;Ranjan et al 2017a;Lingam & Loeb 2017b,c).…”

Sheath-accumulating Propagation of Interplanetary Coronal Mass Ejection

“…The possible impacts of superflares on space weather and terrestrial environment have been vigorously discussed (Miyake et al 2012;Schrijver et al 2012;Shibata et al 2013;Tsurutani & Lakhina 2014;Hayakawa et al 2015;Airapetian et al 2016;Takahashi et al 2016).…”