Habitable Planetary States, the Evolution of Microbial Life, and their Astronomical Biosignatures


Throughout its billions of years of history, Earth has undergone extreme transitions in surface, ocean, and atmospheric chemistry, yet maintained consistently habitable conditions despite a steadily brightening host star. Both the dramatic transformation of our planet over time and its persistent habitability are inextricably linked to the development and evolution of microbial life. This synergy team seeks to unify our understanding of the co-evolution of microbial life, along with its metabolic needs and products, with its dynamic planetary environment. With an eye to near future astronomical searches for life outside our solar system, we will work to use this knowledge to enhance our understanding of the range of remotely detectable atmospheric and surface biosignatures. Earth is not a single example of a habitable world, but through time represents a diverse spectrum of habitable planetary states, perhaps analogs to the ensemble of terrestrial habitable zone exoplanets to be characterized in the coming decades.

This working group seeks to share expertise to productively address synergizing key questions. These key questions are themselves informed by the guiding themes based on member team priorities and tasks.

Key questions

  • What intrinsic properties of our planet have promoted its persistent habitability over billions of years?
  • How has life’s co-evolution with the planetary environment led to positive and negative feedbacks on the Earth system?
  • How has Earth maintained persistent habitability in the presence of a brightening Sun and the co-evolution of life with its associated feedbacks?
  • Which planetary and life processes are most important for understanding the mechanisms that lead to a build up of biosignature gases?
  • What is the full range of remotely detectable atmospheric and surface biosignatures presented by a dynamic and evolving Earth through its history?

Guiding Themes

  • The delivery of life-essential materials to Earth (NASA Ames)
  • The evolution of key microbial metabolisms (Montana, UCR, USC, UCB, Univ. Wisconsin, JPL)
  • The evolution of eukaryotes and advanced microbial metabolisms (Montana, UCR, MIT)
  • The transfer of microbial metabolic products between the subsurface, surface, ocean and atmosphere (USC, UCR, UCB, JPL)
  • The influence of photochemistry on atmospheric composition (UCR, VPL)
  • The effect of metabolic products on climate (UCR, VPL)
  • The dependence of biological productivity on environmental conditions (UCB, UCR, VPL)
  • Early Mars as a habitable environment, and the effect of the presence or absence of life on that environment (SETI Institute, Univ. Wisconsin, VPL, MIT)

Workshop Without Walls: Upstairs Downstairs

A NExSS/NAI/NSF Joint Workshop
February 17th – 19th, 2016

2015 Director's Discretionary Fund Projects

Field Campaign: Spectropolarimetry of Primitive Phototrophs as Global Surface Biosignatures
Lead Investigator: Mary “Niki” Parenteau (VPL Team, SETI Institute)
Co-Investigators: William Sparks (VPL Team, Space Telescope Science Institute), Charles Telesco (University of Florida), Thomas Germer (National Institute of Standards and Technology), C.H.L. Lucas Patty (Vrije Universiteit Amsterdam), Frank Robb (University of Maryland), Victoria Meadows (VPL Team, University of Washington)

This proposal seeks to characterize surface biosignatures associated with anoxygenic phototrophs and cyanobacteria. Circular polarization spectra of environmental samples of microbial mats containing cyanobacteria and anoxygenic phototrophs will be measured in a one-week field campaign in Yellowstone National Park using a newly developed CubeSat-scale spectropolarimeter. This proposal is a collaboration between the NAI VPL team and a Dutch group, including an early career scientist. The project is relevant to the Habitable Planetary States, Evolution of Microbial Life, and Astronomical Biosignatures synergy theme. In addition, use of flight relevant instrumentation, including a newly developed spectropolarimeter, strengthens the project. The co-investigators include VPL and SETI team members along with many co-Is not formerly associated with the NASA astrobiology community, which may lead to new institutional involvements.

Did the Proterozoic Earth have remotely detectable O3, CH4 and N2O? Implications for Terrestrial Exoplanet Analogs and the Search for Life Outside the Solar System
Lead Investigator: Edward Schwieterman (VPL Team, University of Washington)
Co-investigators: Victoria Meadows (VPL Team, University of Washington), Timothy Lyons (Alternative Earths Team, University of California Riverside), Shawn Domagal-Goldman (VPL Team, NASA Goddard Space Flight Center), Noah Planavsky (Alternative Earths Team, Yale), Chris Reinhard, (Alternative Earths Team, Georgia Tech), Giada Arney (VPL Team, University of Washington), Tyler Robinson (VPL Team, University of California Santa Cruz)

Using proven coupled climate-photochemical models to create a small suite of standard, hypothetical chemical profiles for the Proterozoic Earth (0.8-2.5 Ga), this proposal intends to evaluate the detectability of the biogenic gases CH4, N2O, and O2/O3 during that eon. The simultaneous detection of these gases would have signaled a strong disequilibrium biosignature to a distant observer. The research conducted under this proposal will allow us to apply knowledge of the ancient Earth to the study of exoplanets, and provide a foundation for further collaboration between the Virtual Planetary Laboratory (VPL) and Alternative Earths NAI teams. The proposal provides a strong foundation for the Habitable Planetary States, the Evolution of Microbial Life, and their Astronomical Biosignatures synergy theme. This work will contribute to the training of an early career astrobiologist by funding a graduate student/transitioning postdoctoral scientist who will receive interdisciplinary training at the nexus between two NAI teams.

Integrating the Geochemical and Genomic History of the Rise of Oxygen on Earth
Lead Investigator: Greg Fournier (MIT Team)
Co-investigator: Tim Lyons (NAI Alternative Earths Team, University of California Riverside)

The work proposed will investigate evidence for the history of oxygen within the genes and genomes of organismal lineages that persisted through the Great Oxygenation event and the Neoproterozoic event. The investigators propose to study the rate and pattern of the acquisition and loss of genes coding for oxygen-associated enzymes in diverse microbial groups over time, as a proxy for changing oxygen levels on geological timescales. This bioinformatics approach will strongly complement current studies of the rise of oxygen being conducted by the NAI Alternative Earths Team at UC Riverside by providing independent support for specific hypotheses, as well as resolving several currently ambiguous narratives. The project brings together the Evolution of Complex Life Synergy Group with Co-I Lyons and the UC Riverside NAI team and provides support for an early career researcher.