1. About Exobiology

    NASA’s Exobiology and Evolutionary Biology Program, an element of the Astrobiology Program, supports research into the origin and early evolution of life, the potential of life to adapt to different environments, and the implications for life elsewhere. Exobiology and evolutionary biology research is conducted in the context of NASA’s ongoing exploration of our stellar neighborhood and efforts to detect and identify biosignatures – that is, clear signs of life – by in situ and remote sensing methods. Areas of research emphasis in the Exobiology and Evolutionary Biology Program are: planetary conditions for life, prebiotic evolution, early evolution of life and the biosphere, and evolution of advanced life.

    Research in the area of planetary conditions for life seeks to delineate galactic and planetary conditions conducive to the origin of life. Topics of interest include the formation and stability of habitable planets, the formation of complex organic molecules in space and their delivery to planetary surfaces, models of early environments in which organic chemical synthesis could occur, the forms in which prebiotic organic matter has been preserved in planetary materials, and the range of planetary environments amenable to life. Research into planetary conditions for life also encompasses studies of sites thought to be analogues of early Earth or other planetary environments with the potential to harbor life.

    Laboratory and theoretical studies in the area of prebiotic evolution seek to understand the pathways and processes leading from the origin of planetary bodies to the origin of life. Research in this area aims to investigate planetary and molecular processes that established the physical and chemical conditions within which living systems may have arisen. A major objective of prebiotic evolution research is to determine what chemical systems could have served as precursors of metabolic and replicating systems on Earth and elsewhere, including alternatives to the current DNA/RNA-protein basis for life.

    The goal of research in the area of early evolution of life and the biosphere is to determine the nature of the most primitive organisms and the environments in which they evolved. Investigations in this area focus on two natural repositories of evolutionary history on Earth: the molecular record in living organisms, and the geological record. Researchers can use these records to determine when and where life first appeared and what the earliest living organisms were like and understand the phylogeny (evolutionary history) and physiology of microorganisms, including extremophiles. They can use them to explore the original nature of cellular energy transfer, membrane function, and information processing; and to investigate the development of key biological processes and their environmental impact. These records can also help researchers to understand the response of Earth’s biosphere to extraterrestrial events; investigate the evolution of genes, metabolic pathways, and microbial species subject to long-term environmental change; and study the coevolution of, and interactions within, microbial communities that drive major geochemical cycles.

    Research into the evolution of advanced life seeks to determine the biological and environmental factors leading to the development of multicellular life on Earth and the potential distribution of complex life in the Universe. This research includes studies of the origin and early evolution of biological factors essential to multicellular life, such as intercellular signaling, programmed cell death, the cell cytoskeleton (internal cell structure), cellular adhesion control, and cell differentiation (specialization). Research in this area also includes evaluation of environmental factors such as the influence of extraterrestrial events (for example, meteorite impacts, orbital and solar variations, gamma-ray bursts) and planetary processes (for example, so-called Snowball Earth or glaciation events, rapid climate change) on the appearance and evolution of multicellular life. Of particular interest are mass extinction events.

    Recent projects supported by the Exobiology and Evolutionary Biology Program include a search for traces of life in Earth’s oldest sedimentary rocks, found in the Isua Supracrustal Belt in southern West Greenland; studies of species loss and ecological recovery following mass extinction events on early Earth; isotopic analysis of organic elements and compounds in meteorites and interplanetary dust particles; studies of mechanisms of prebiotic geochemistry (reduction reactions on mineral surfaces) and the role of minerals in prebiotic chemistry; characterization of magnetofossils (magnetic minerals left in rocks by microbes that are responsive to magnetic fields) as a novel biosignature of ancient ecosystems; and theoretical studies of the extraterrestrial chemistry of biogenic elements and compounds.