Tracing the ingredients for a habitable earth from interstellar space through planet formation

Edwin A. Bergin, Geoffrey A. Blake, Fred Ciesla, Marc M. Hirschmann, Jie Li

Research output: Contribution to journalArticlepeer-review

79 Scopus citations

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 macromolecular (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 bulk silicate Earth 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.

Original languageEnglish (US)
Pages (from-to)8965-8970
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume112
Issue number29
DOIs
StatePublished - Jul 21 2015

Bibliographical note

Publisher Copyright:
© 2015, National Academy of Sciences. All rights reserved.

Keywords

  • Comets
  • Elements
  • Interstellar medium
  • Meteorites
  • Terrestrial worlds

Fingerprint

Dive into the research topics of 'Tracing the ingredients for a habitable earth from interstellar space through planet formation'. Together they form a unique fingerprint.

Cite this