Exobiology 



and the periodic cycles of climatic changes arising from the Milankovich cycles of 

 orbital effects in the Earth-Moon-Sun system. The influence of the Milankovich 

 cycles on climate over the last 500,000 years has been well documented, and 

 evidence for such effects deeper in the past is being sought. The discovery of 

 platinum group elemental anomalies in samples from global distributions of 

 sediments deposited about 65 million years ago has led to the theory that impacts 

 were responsible for mass extinctions at the Cretaceous-Tertiary Boundary. That 

 these extinctions were followed by the rise of mammals to dominance underscores 

 the need to assess the occurrence of such phenomena throughout the history of 

 life. In addition to laboratory studies of the geological record, theoretical studies 

 should be carried out to predict the perturbations of the terrestrial environment 

 caused by large asteroidal impacts and the biological consequences of the resulting 

 physical and chemical perturbations. Evidence of these predictions should be 

 sought in the rocks that record the extinctions. 



Understanding the relationship between biological evolution and the influences of 

 endogenous planetary processes and exogenous astrophysical processes will 

 require the gathering of information from diverse sources to construct a 

 comprehensive paleontological data system. This system should incorporate 

 detailed analysis of the fossil record of extinctions to the genus level; geological, 

 geochemical, and paleoenvironmental data associated with that record; and 

 corresponding data on the cratering record of impacts. With this data base, it 

 should also be possible to assess the existence of periodicity in mass extinctions. 

 Once found, the relationship, if any, can be determined between the periodicity 

 and the records of extraterrestrial phenomena, such as impact craters on the 

 Earth, Moon, or Mars; changes in the tidal interaction of the Moon and Earth; 

 and variation of insolation resulting from cyclic and noncyclic changes in the orbit 

 and axial inclination of the Earth. 



Findings for Evolution of Advanced Life 



• A new and exciting interdisciplinary field of science has emerged as it has 

 become increasingly clear that, in addition to the effects of intrinsic geological 

 activity, extraterrestrial phenomena due to Earth's cosmic environment may 

 have played a critical role in influencing the course of biological evolution. 



• The historical record of astrophysical phenomena, particularly asteroidal or 

 cometary impacts, may be preserved in the rocks of the Moon and Mars. 



Recommendations 



• The Life Sciences and Solar System Exploration Divisions of OSSA should 

 increase support of research designed to determine the occurrence of 

 elemental anomalies and other extraterrestrial signatures in the sedimentary 

 record and their correlation with contemporaneous changes in the 

 composition of fossil biota. 



• NASA should include in its scientific objectives for future exploration of the 

 Moon and Mars the search for evidence of impacts or other astrophysical 

 phenomena that may be time correlated with analogous occurrences on 

 Earth. 



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