Precambrian Fossil Record

  1. Geological terranes in the Archæan Eon:
    1. High Grade Gneisses
      1. example: the Isua Supracrustals (west Greenland) at 3.85 Ga
    2. Greenstone Belts
      1. Volcaniclastics (These silicified sediments form the rock type, chert, where putative fossils have been found
      2. banded iron formation (BIF)
      3. pillow lavas (the greenstones)
    3. examples of Greenstone Belts where "fossils" have been found:
      1. Pilbara Block in West Australia
      2. Barberton Greenstone Belt, South Africa
    4. Age: 3.85 to about 2.5 Ga
  2. Archæan fossils
    1. chemical fossils
      1. organic molecules of complex composition leave behind remains that appear to have come from known, biogenic molecules

      2. Apatite
      3. 13C/12C values indicate biogenicity in rocks from West Greenland. Living systems at 3.8 Ga?
    2. putative cellular remains: These microspheres are from the Barberton Greenstone Belt and have an age of 3.4 Ga. They are quite small, generally less tham 10 microns.



    3. stromatolites: (not yet figured) make up probably the most convincing evidence for early phosynthetic life, beginning about 2.8 to 2.7 Ga. There are somewhat convincing stromatolites from Southwest Africa (Namibia) at about 3.0 Ga.
  3. The Proterozoic Fossil Record
    1. Gunflint Biota
      1. Schreiber Beach Biofacies: This stromatolitic biofacies dominated by an admixture of simple spheres (Unnammed, really, but perhaps indistuingishable from Sphaerophycus) with the thin, rod-shaped Gunflintia and rarer Huroniospora
      2. Frustration Bay biofacies is dominated by Kakabekia and Galaxiopsis with rare clusterrs of Leptoteichos, a perfectly spherical cell though to be a plantonic floater.
      3. All of about 2 Ga in age and generally associated with bif (Banded Iron Formation)
    2. Cherty Carbonate Biotas
      1. Generally younger in age, most are late Proterozoic, <900 Ma
      2. dominated by cyanobacteria. Cyanobacteria are O2-producing photosynthetic autotrophes.
      3. Photosof some common cyanobacterial genera.
      4. More photos of cyanobacteria from Purdue University.
      5. either stromatolitic or found as laminated cyanobacterial mats
      6. excellent preservation, due to properties of chert (SiO2)
      7. examples from the Narssarssuk Formation, ca. 700 Ma from NW Greenland

        Spaerophycus parvum: small spherical cyanobacterial cells, many enclosed within a sheath. These cells are preserved in colonies, populations of cells, that inhabited intertidal and shallow water carbonate-rich environments, forming laminated mats.

        Eoentophysalis sp. are cyanobacteria similar to the extant genus Entophysalis. These cells form populations today that are embedded in thick extra-cellular sheath material thought to be useful in shielding harmful UV radiation. This adaptation would have enabled these cyanobacteria to live in periodically exposed habitats, such as supratidal carbonate mats.

    3. Palynonorphs
      1. generally thought to be resting cysts of eukaryotic, planktonic algae
      2. found in shales, rare in cherts
      3. cellular details not preserved
    4. Macrofossils
      1. Vendotaenia: sheet-like, possible alga

      2. Tawuia - Chuaria, classic problem in morphologic boundary-setting.

Web Resources

  • A web-based site on Precambrian life from Carleton College that includes a primer on how stromatolites grow.
  • A note on evidence for living systems at 3.8 Ga.

update 26 October 2000.