Robin Kodner: Bringing genomics to geobiology

Fate of the organic molecules generated by primary productivity in the surface ocean:

  • carbohydrates, proteins, and nucleic acids (biological pump acts on these)
  • lipids and structural polymers (diagenesis turns these into organic fossils, kerogen, & bitumen (oil)

Organismal part of talk (examples of sterols used as biomarkers)

  1. diversity of sterols and steranes (branches can indicate phylogeny)
  2. C_30 isopropylcholesterol likely associated with sponges

Population level (metagenomics)

  1. C_29 steranes (dominant [relative to C28} in Paleozoic)
  2. One explanation is that C29 may be typical of green algae, while C28 indicate modern phytoplankton (that arose ~200 Mya)
  3. But C29 sterols are made by MANY eukaryotes.  Green algae (Charophyceae) are implicated because they have a good fossil record back into the Paleozoic).
  4. Ternary diagram shows that Prasinophytes (likely modern analog of the Paleozoic green algae) have lower C29/C28 ratio than groups of green algae [Kodner, Geobiology, 2008]
  • Advantage of studying modern orgs is that nucleic acids are available for taxonomic survey, in addition to lipids.
  • Sequence a aggregated sample, compare with sequence database, use search alignment tool (BLAST), and compare with reference sequences to get reference phylogeny

My Qs:

Where does all the sulfur come from in crude oil?

Is it clear that diagenesis does not degrade sterol structure?  If so, what organisms generated the fossil molecules we call fuel?