Cosmic Rays and Terrestrial Life: A Brief Review (1211.3962v3)

Abstract: "The investigation into the possible effects of cosmic rays on living organisms will also offer great interest." - Victor F. Hess, Nobel Lecture, December 12, 1936 High-energy radiation bursts are commonplace in our Universe. From nearby solar flares to distant gamma ray bursts, a variety of physical processes accelerate charged particles to a wide range of energies, which subsequently reach the Earth. Such particles contribute to a number of physical processes occurring in the Earth system. A large fraction of the energy of charged particles gets deposited in the atmosphere, ionizing the atmosphere, causing changes in its chemistry and affecting the global electric circuit. Remaining secondary particles contribute to the background dose of cosmic rays on the surface and parts of the subsurface region. Life has evolved over the past ~ 3 billion years in presence of this background radiation, which itself has varied considerably during the period. As demonstrated by the Miller-Urey experiment, lightning plays a very important role in the formation of complex organic molecules, which are the building blocks of more complex structures forming life. There is growing evidence of increase in the lightning rate with increasing flux of charged particles. Is there a connection between enhanced rate of cosmic rays and the origin of life? Cosmic ray secondaries are also known to damage DNA and cause mutations, leading to cancer and other diseases. It is now possible to compute radiation doses from secondary particles, in particular muons and neutrons. Have the variations in cosmic ray flux affected the evolution of life on earth? We describe the mechanisms of cosmic rays affecting terrestrial life and review the potential implications of the variation of high-energy astrophysical radiation on the history of life on earth.

Cosmic Rays and Terrestrial Life: An Overview

The paper by Dimitra Atri and Adrian L. Melott examines the multifaceted impacts of cosmic rays on terrestrial life and atmospheric processes. Cosmic rays, originating from both local and distant astrophysical events, influence Earth through a variety of mechanisms, including atmospheric ionization, alteration of atmospheric chemistry, and biological radiation exposure.

Cosmic Ray Sources and Variations

The origin of cosmic rays is diverse, ranging from solar activity to galactic phenomena such as supernovae. Importantly, the flux of cosmic rays reaching Earth can vary due to both periodic cycles, like the solar magnetic field's 11-year cycle, and non-periodic events, such as nearby supernovae and interactions with dense interstellar clouds. These variations affect the biosphere through changes in radiation dose.

Interaction with the Atmosphere

Cosmic rays penetrating the Earth's atmosphere initiate electromagnetic interactions, leading to ionization. This process influences atmospheric electricity, notably impacting thunderstorm formation through the initiation of electric breakdown in thunderclouds. Ionization also affects atmospheric chemistry, particularly through the production and depletion of ozone, critical for shielding life from harmful UV radiation. Neutrons and muons generated during cosmic ray interactions further contribute to potential hazards, with muons capable of penetrating deep into the Earth's crust and posing significant biological risks.

Biological Implications

Cosmic rays have implications for both the origin and evolution of life. Increased lightning rates, potentially stimulated by cosmic rays, may have been instrumental in the formation of complex organic molecules during Earth's early history. In terms of evolution, cosmic rays can induce mutations through DNA damage. This aspect is crucial for understanding how radiation bursts from astrobiological events may have catalyzed evolutionary processes. The paper underscores periodic cosmic ray bursts as potential drivers for observable biodiversity fluctuations over geological timescales.

Future Research and Considerations

The paper advocates for further research to improve the understanding of cosmic ray production mechanisms and their terrestrial impacts. Specifically, studies on radiation damage from muons and other secondary particles are necessary to elucidate their effects on varying biological organisms. Considering the complexity of living systems, the translation of radiation damage into broad evolutionary consequences remains a significant challenge.

Overall, this research highlights the intricate relationship between cosmic rays and life on Earth, urging a comprehensive exploration of cosmic influences from biological, atmospheric, and evolutionary perspectives. The implications of this paper extend into future investigations of astrophysical influence on terrestrial life, necessitating multidisciplinary collaboration to deepen our understanding of these cosmic interactions.