Quantifying the Origins of Life on a Planetary Scale

Quantifying the Origins of Life on a Planetary Scale

Authors:

Scharf et al

Abstract:

A simple, heuristic formula with parallels to the Drake Equation is introduced to help focus discussion on open questions for the origins of life in a planetary context. This approach indicates a number of areas where quantitative progress can be made on parameter estimation for determining origins of life probabilities. We also suggest that the probability of origin of life events can be dramatically increased on planets with parallel chemistries that can undergo the development of complexity, and in solar systems where more than one planet is available for chemical evolution, and where efficient impact ejecta exchange occurs, increasing the effective chemical search space and available time.

The UltraViolet Light Environment is VERY Important for Prebiotic Chemistry

Influence of the UV Environment on the Synthesis of Prebiotic Molecules

Authors:

Ranjan et al

Abstract:

Ultraviolet (UV) radiation is common to most planetary environments, and could play a key role in the chemistry of molecules relevant to abiogenesis (prebiotic chemistry). In this work, we explore the impact of UV light on prebiotic chemistry that might occur in liquid water on the surface of a planet with an atmosphere. We consider effects including atmospheric absorption, attenuation by water, and stellar variability to constrain the UV input as a function of wavelength. We conclude that the UV environment would be characterized by broadband input, and wavelengths below 204 nm and 168 nm would be shielded out by atmospheric CO2 and water, respectively. We compare this broadband prebiotic UV input to the narrowband UV sources (e.g. mercury lamps) often used in laboratory studies of prebiotic chemistry, and explore the implications for the conclusions drawn from these experiments. We consider as case studies the ribonucleotide synthesis pathway of Powner et al (2009) and the sugar synthesis pathway of Ritson et al (2012). Irradiation by narrowband UV light from a mercury lamp formed an integral component of these studies: we quantitatively explore the impact of more realistic UV input on the conclusions that can be drawn from these experiments. Finally, we explore the constraints solar UV input places on the buildup of prebiotically important feedstock gasses like CH4 and HCN. Our results demonstrate the importance of characterizing the wavelength dependence (action spectra) of prebiotic synthesis pathways to determine how pathways derived under laboratory irradiation conditions will function under planetary prebiotic conditions.

Surface/atmospheric Abundances of Bio-Necessary Materials may be VERY Variable in Terrestrial Exoplanets

Tracing the Ingredients for a Habitable Earth from Interstellar Space through Planet Formation

Authors:

Bergin et al

Abstract:

We use the C/N ratio as a monitor of the delivery of key ingredients of life to nascent terrestrial worlds. Total elemental C and N contents, and their ratio, are examined for the interstellar medium, comets, chondritic meteorites and terrestrial planets; we include an updated estimate for the Bulk Silicate Earth (C/N = 49.0 +/- 9.3). Using a kinetic model of disk chemistry, and the sublimation/condensation temperatures of primitive molecules, we suggest that organic ices and macro-molecular (refractory or carbonaceous dust) organic material are the likely initial C and N carriers. Chemical reactions in the disk can produce nebular C/N ratios of ~1-12, comparable to those of comets and the low end estimated for planetesimals. An increase of the C/N ratio is traced between volatile-rich pristine bodies and larger volatile-depleted objects subjected to thermal/accretional metamorphism. The C/N ratios of the dominant materials accreted to terrestrial planets should therefore be higher than those seen in carbonaceous chondrites or comets. During planetary formation, we explore scenarios leading to further volatile loss and associated C/N variations owing to core formation and atmospheric escape. Key processes include relative enrichment of nitrogen in the atmosphere and preferential sequestration of carbon by the core. The high C/N BSE ratio therefore is best satisfied by accretion of thermally processed objects followed by large-scale atmospheric loss. These two effects must be more profound if volatile sequestration in the core is effective. The stochastic nature of these processes hints that the surface/atmospheric abundances of biosphere-essential materials will likely be variable.

AAAS Alternate Biochemistries Panel Tomorrow @ 3 PM in San Jose

Ideas about directing evolution of life forms on Earth and finding life on other planets are rapidly morphing from science-fiction fantasy into mainstream science, says David Lynn, a chemist at Emory University.

"These areas of science are rapidly coming of age because of our increasing knowledge and advancing technology. It's an exciting time. We're on the threshold of answering fundamental questions including: What is life? Are there forms of life that we haven't even yet imagined? Are we alone in the universe?"

A panel discussion, "Searching for Alternative Chemistries of Life on Earth and Throughout the Universe," is set for Friday, February 13, at 3 pm, during the annual meeting of the American Association for the Advancement of Science (AAAS) in San Jose. Lynn co-organized the panel with Jay Goodwin, a senior Emory research fellow and an AAAS Science and Technology Policy Fellow.

link.