1. Editorial

   • Mitchell K. Hobish
   • Cyril Ponnamperuma

   EditorialNotes Pages: 219 - 219

2. Life as a planetary phenomenon

   • Tobias Owen

   Planetary Atmospheres Pages: 221 - 234

3. Habitability of the early earth: Clues from the physiology of nitrogen fixation and photosynthesis

   • Kenneth M. Towe

   Planetary Atmospheres Pages: 235 - 250

4. Crustal evolution in the early precambrian

   • S. Moorbath

   Planet Earth Pages: 251 - 261

5. Carbon isotope discrepancy between precambrian stromatolites and their modern analogs: Inferences from hypersaline microbial mats of the sinai coast

   • Manfred Schidlowski

   Planet Earth Pages: 263 - 277

6. Methane and chlorocarbons in the earth's atmosphere

   • F. Sherwood Rowland

   Planet Earth Pages: 279 - 297

7. The photochemistry of biogenic gases in the early and present atmosphere

   • Joel S. Levine
   • Tommy R. Augustsson

   Planet Earth Pages: 299 - 318

8. The science of the biosphere

   • Daniel B. Botkin

   Life On Earth Pages: 319 - 325

9. Submarine hydrothermal vents and associated gradient environments as sites for the origin and evolution of life

   • John A. Baross
   • Sarah E. Hoffman

   Life On Earth Pages: 327 - 345

10. The microbial community at laguna Figueroa, Baja California Mexico: From miles to microns

    • John F. Stolz

    Life On Earth Pages: 347 - 352

11. Air-sea-land interactions: Global and regional habitability

    • J. Shukla

    The Present Pages: 353 - 363