The effect of particle precipitation events on the neutral and ion chemistry of the middle atmosphere: II. Odd hydrogen

Ionizing radiation is a ubiquitous feature of the Cosmos, from exogenous cosmic rays (CR) to the intrinsic mineral radioactivity of a habitable world, and its influences on the emergence and persistence of life are wide-ranging and profound. Much attention has already been focused on the deleterious effects of ionizing radiation on organisms and the complex molecules of life, but ionizing radiation also performs many crucial functions in the generation of habitable planetary environments and the origins of life. This review surveys the role of CR and mineral radioactivity in star formation, generation of biogenic elements, and the synthesis of organic molecules and driving of prebiotic chemistry. Another major theme is the multiple layers of shielding of planetary surfaces from the flux of cosmic radiation and the various effects on a biosphere of violent but rare astrophysical events such as supernovae and gamma-ray bursts. The influences of CR can also be duplicitous, such as limiting the survival of surface life on Mars while potentially supporting a subsurface biosphere in the ocean of Europa. This review highlights the common thread that ionizing radiation forms between the disparate component disciplines of astrobiology.

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Ionizing radiation and life.

In the past decade, it has become apparent that the importance of magnetic interactions is not confined to the world of physics but extends into the realm of physiology and whole organism biology. That this should be so follows from two elementary observations: (1) by virtue of their magnetic moments and electrical charges, the atoms and ions which make up an organism can magnetically interact with the organism’s environment, and (2) the environment of practically every organism includes a highly ordered and stable (relative to the lifetime of the organism) geomagnetic field which contains both spatial and temporal information of potential value to the organism.

The Geomagnetic Field Its Nature, History, and Biological Relevance

During the past century over 1,000 articles have been published claiming or refuting a correlation between some aspect of solar activity and some feature of terrestrial weather or climate. Nevertheless, the sense of progress that should attend such an outpouring of ‘results’ has been absent for most of this period. The problem all along has been to separate a suspected Sun–weather signal from the characteristically noisy background of both systems. The present decade may be witnessing the first evidence of progress in this field. Three independent investigations have revealed what seem to be well resolved Sun–weather signals, although it is still too early to have unreserved confidence in all cases. The three correlations are between terrestrial climate and Maunder Minimum-type solar activity variations, a regional drought cycle and the 22-yr solar magnetic cycle, and winter hemisphere atmospheric circulation and passages by the Earth of solar sector boundaries in the solar wind. The apparent emergence of clear Sun–weather signals stimulated numerous searches for underlying physical causal links.

Solar–terrestrial influences on weather and climate

The paleomagnetic record of recent lake and marine sediments contains anomalous magnetic directions which have been interpreted as large-scale fluctuations of the geomagnetic field (excursions). In view of the many ways in which isolated distortions of the paleomagnetic recording process can arise, proof of the existence of an excursion must depend on consistent results from within a given lake or marine environment as well as from adjacent sedimentary environments. A critical review of the proposed excursions reveals that although some excursions probably did occur, there is not yet sufficient evidence to confirm the existence of many of the claimed excursions. When the existence of regional or global excursions is established, additional information will become available on the nature of the geomagnetic field, on the use of excursions as time-stratigraphic horizons, and on possible correlations between geomagnetic activity and climatic change.

Geomagnetic excursions and their paleomagnetic record

There is mounting evidence that past extinctions of faunal species have occurred in near coincidence with reversals in polarity of the geomagnetic field. Could the link lie in catastrophic depletions of stratospheric ozone caused by solar-proton irradiation over a reduced geomagnetic field?

T. E. Holzer

Papers

Influence of ancient solar-proton events on the evolution of life