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The Astrophysical Context of Life
Context and Statement of Task
This study is proposed to address issues raised in the recent assessment of astrobiology programs at NASA (Life in the Universe: An Assessment of U.S. and International Programs in Astrobiology, 2002). The committee that wrote the report found that research in certain key areas of astrophysics relevant to understanding the astronomical environment in which life arose on Earth (and, potentially, elsewhere in the universe) was not well represented within the broad range of issues being addressed by NASA’s Astrobiology program. This report is intended to highlight the potential contributions astronomers can make to the new field of astrobiology.
Life on Earth originated and has evolved over the last 3.5 billion plus years in a complex and highly variable astronomical environment. The Earth was assembled from interstellar gas already enriched in prebiotic molecules that were themselves the product of generations of stellar nucleosynthesis and chemical evolution in interstellar clouds. Asteroid and comet impacts have apparently altered the course of evolution, and interstellar dust continues to sift down onto the Earth. Long-lived radioactivities from stellar explosions heat Earth’s molten core, driving plate tectonics, and suffuse the mantle in the form of potassium-40.
Life on or near to the surface of the Earth is strongly affected by the evolving radiation output from the Sun, interrupted by solar flares. Life is exposed to a continuous flux of cosmic rays that has probably varied significantly over geological times. Statistically, the Earth has been exposed to perhaps thousands of jolts of biologically significant radiation from supernovae and the possibility of exposure to an exotic event such as a gamma-ray burst has been considered.