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Planetary Habitability and Evolution of Biological Complexity

Research in the astrobiology program of the University of Washington Team is an integrated, multidisciplinary effort that is concentrated on four broad questions concerned with planetary habitability and evolution of biological complexity:

• How often do planets with truly Earth-like properties form?
• How important is plate tectonics in the formation and maintenance of metazoan life?
• How important are mass extinctions for the evolution and extinction of complex life? Are mass extinctions fertilizer or poison (or both) in the garden of complex organisms?
• What are the evolutionary pathways by which complex organisms originate from microbes?

Planetary Habitability

Earth provides clues as to how geophysical, geochemical, and astrophysical processes help create and sustain habitable planets. In addition to liquid water and organic compounds, a habitable planet must make available a full range of energy sources, chemical compounds, and elements for oxidation and reduction reactions necessary for life. Additionally, life must have the flexibility to co-evolve with various organisms to form and maintain multiple habitats.

A differentiated planet with liquid water, active tectonism, and volcanism could sustain microbial life. On Earth, the accumulation of oxygen was key to the origin and evolution of metazoans. A habitable planet that could support metazoans, as we know them, would have to develop a carbon dioxide atmosphere that is modulated to create temperate conditions and allow the evolution of oxygenic photosynthesis and the formation of an ozone layer to limit ultra violet effects on organisms. It can also be argued that periodic catastrophic events including bolide impacts are also necessary to create and maintain high variability of habitable conditions that result in increased biodiversity and biocomplexity. The University of Washington Team research investigates questions concerning conditions for life habitability.

Evolution of Biological Complexity

The University of Washington Team deals with two major areas to study questions concerning the rise of biocomplexity.

• Fossil Record on Earth
  Very little is known about the origin of metazoans, other than they appear in the fossil record between 700 and 600 million years ago, in conjunction with the accumulation of relatively high concentrations of oxygen in the atmosphere. One of our hypotheses is that the earliest group of heterotrophic metazoans used anaerobic microbial communities (consortia) in their gut to decompose the complex organic compounds left behind by dead microbes. Many invertebrates and some vertebrates still employ microbes as their source of digestive enzymes. The metabolic community of microorganisms that comprised this gut flora still exists today, probably in aquatic microbial mats. Did lateral gene transfer occur between these gut microbes and metazoans, and what genes would likely be transferred?
• Study of Living Organisms
  Genomics has already proven to be useful for addressing questions of early life and the evolution of eukaryotes. To date, more than 50 bacterial and archaeal genomes have been sequenced or are in progress. One of the conundrums from the genome sequences is that up to 50% of the open reading frames in genomes from microorganisms encode for unknown proteins. Moreover, some of the enzymes involved in metabolic pathways known to be present in the organism are absent in the genome. Are the pathways incomplete, or are enzymes with unknown sequences or low sequence homology involved?