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Project Reports

• Biosphere-Geosphere Stability and the Evolution of Complex Life

  Both the rise of complex life and the Phanerozoic mass extinctions are accompanied by significant perturbations of the carbon cycle. Attention is usually focused on causality, and environmental change is almost always considered the driver. Yet the co-evolution of life and the environment suggests that the fundamental issue is not causality but rather stability. This project seeks to develop a theory of biosphere-geosphere stability and to test it using the geochemical and fossil records.

  ROADMAP OBJECTIVES: 4.2 4.3 5.2 6.1

• Biosignatures in Ancient Rocks – Kump Group

  We are analyzing FAR-DEEP cores that span the putative “oxygen overshoot” associated with the termination of the Great Oxidation Event, 2.0 billion years ago. The volcanic rocks in question are highly oxidized. Our hypothesis is that oxygen-enriched groundwaters altered these rocks during a time interval when atmospheric oxygen concentrations approached modern levels, falling subsequently to lower values characteristic of the ensuing billion years. Kump has also proposed a new explanation for the “second rise of atmospheric oxygen” in the Neoproterozoic (ca. 850 Ma).

  ROADMAP OBJECTIVES: 1.1 4.1 4.2 4.3 5.2 6.1

• Disks and the Origins of Planetary Systems

  This task is concerned with the evolution of complex habitable environments. The planet formation process begins with fragmentation of large molecular clouds into flattened disks. This disk is in many ways an astrochemical “primeval soup” in which cosmically abundant elements are assembled into increasingly complex hydrocarbons and mixed in the dust and gas within the disk. Gravitational attraction among the myriad small bodies leads to planet formation. If the newly formed planet is a suitable distance from its star to support liquid water at the surface, it is in the so-called “habitable zone.” The formation process and identification of such life-supporting bodies is the goal of this project.

  ROADMAP OBJECTIVES: 1.1 1.2 2.2 3.1 4.1 4.3

• Project 3: Impact History of the Earth-Moon System

  The influx of interplanetary debris onto the early Earth represents a major hazard to the emergence of life. Large crater-forming bodies must have been common in the early solar system, as craters are seen on all ancient solid surfaces from Mercury to the moons of the outer planets. Impact craters are few in number on the Earth today only because geologic activity and erosion gradually erase them. The Earth’s nearest neighbor, the Moon, lacks an atmosphere and significant tectonic activity, and therefore retains a record of past impacts. The goal of our research is to reconstruct the bombardment history of the Moon, and by proxy the Earth, to establish when the flux of sterilizing impacts declined sufficiently for the Earth to became habitable.

  ROADMAP OBJECTIVES: 4.3

• Biosignatures in Extraterrestrial Settings

  The Biosignatures in Extraterrestrial Environments group works on finding and characterizing exoplanets, in particular through very high resolution spectroscopy; and developing new techniques for finding exoplanets and characterizing their properties. It also works on understanding the evolution and dynamics of planetary systems, including the solar system, and the role of astrophysical processes in establishing and sustaining life in extraterrestrial environments.

  ROADMAP OBJECTIVES: 1.1 1.2 2.1 2.2 3.1 4.1 4.3 6.2 7.1 7.2

• Evolution of Protoplanetary Disks and Preparations for Future Observations of Habitable Worlds

  The evolution of protoplanetary disks tells the story of the birth of planets and the formation of habitable environments. Microscopic interstellar materials are built up into larger and larger bodies, eventually forming planetesimals that are the building blocks of terrestrial planets and their atmospheres. With the advent of ALMA, we are poised to break open the study of young exoplanetesimals, probing their organic content with detailed observations comparable to those obtained for Solar System bodies. Furthermore, studies of planetesimal debris around nearby mature stars are paving the way for future NASA missions to directly observe potentially habitable exoplanets.

  ROADMAP OBJECTIVES: 1.1 1.2 3.1 4.3 7.2

• Habitable Planet Formation and Orbital Dynamical Effects on Planetary Habitability

  This task explores how habitable planets form and how their orbits evolve with time. Terrestrial planet formation involves colliding rocks in a thin gaseous disk surrounding a newborn star and VPL’s modeling efforts simulate the orbital and collisional evolution of a few to millions of small bodies to determine the composition, mass and orbital parameters of planets that ultimately reach the habitable zone. After formation, gravitational interactions with the star and planet can induce short- and long-term changes in orbital properties that can change available energy to drive climate and illuminate the planetary surface. The VPL simulates these effects in known and hypothetical planetary systems in order to determine the range of variations that permit planetary habitability.

  ROADMAP OBJECTIVES: 1.1 1.2 3.1 4.3

• Biosignatures of Life in Extremely Energy-Limited Environments

  The terrestrial subsurface is the least explored habitat on earth and is characterized by darkness and reducing conditions that limit how fast microbes can obtain energy (low energy fluxes). The diversity and metabolic strategies of microbes in this environment are the subject of our investigation.

  ROADMAP OBJECTIVES: 4.1 4.3 5.1 5.3 7.1

• Fundamental Properties Revealed by Parent Volatiles in Comets

  We studied water and other prebiotic molecules in the atmospheres of comets C/2012 S1 (ISON) and C/2013 R1 (Lovejoy). These projects aim at improved understanding of cometary chemistry – a test bed for the contribution of comets to the delivery of exogenous prebiotic organics and water to early Earth, hypothesized as a precursor event to the emergence of the biosphere.

  ROADMAP OBJECTIVES: 2.2 3.1 4.3

• Project 3A: Searching for Ancient Impact Events Through Detrital Shocked Zircons

  Understanding how quickly planetary surface environments evolve on newly accreted worlds is critical for predicting when habitable conditions are established. The meteorite impact history of the inner solar system strongly indicates that the Earth was subject to a global impact bombardment during the first few hundred million years after accretion. The scope, timing, and consequences of this profound process are hotly debated. This project investigated populations of detrital zircons in Archean sedimentary rocks to search for tell-tale signs of impact processes in the form of shock-induced microstructures that are diagnostic of impact. Such features have been shown to survive in detrital shocked zircons eroded from known impact structures on Earth, including the Vredefort, Sudbury, and Santa Fe craters. We have investigated populations of 1,000 zircons per sample using backscattered electron imaging of grain exteriors with a scanning electron microscope. Thus far we have surveyed zircons separated from rocks collected from the Yilgarn craton (Australia), North China craton (China), Wyoming craton (USA), and the Superior craton (Canada). While intriguing microstructures have been observed, thus far no confirmed shock microstructures have been encountered. Our inability the identify shocked grains in populations of 1,000 zircons (per sample) does not necessarily mean shocked grains are absent; our results provide constraints that if they are present, they are in abundances of <0.1% in the detrital population of the rocks investigated. Our detailed search continues…

  ROADMAP OBJECTIVES: 1.1 4.1 4.3