Grypania spiralis
The oldest known fossils on Earth are 3.5 billion year
old stromatolites and bacterial body fossils from western Australia and
southern Africa. The oldest currently known macroscopic body fossils are Grypania
spiralis - distinctive spirally coiled “algae” - from the Negaunee
Iron-Formation of Michigan’s Upper Peninsula (UP). They come from the
“fossiliferous zone” of the lower “magnetite-carbonate-silicate-chert iron
formation” interval of the lower Negaunee Iron-Formation (= unit 2 of Han in
Gair, 1975, USGS Professional Paper 769: 77), upper Menominee Group,
Marquette Range Supergroup. The Negaunee Fe-Fm. dates to the
mid-Paleoproterozoic, at 2.11 billion years, although a 1.874 billion year date
for this unit was published in the 2000s.
Fossil material from this area has been documented in
Han & Runnegar (1992) (Science 257: 232-235). The samples
shown below are from the same locality cited in the Han & Runnegar (1992)
paper. They come from the Empire Mine, an open-pit iron mine exploiting
the Negaunee Fe-Fm. The Empire Mine is just northwest of the town of
Palmer & southeast of the town of Ishpeming, in Marquette County (western
UP of Michigan). Pit location: 46° 27’ 18” North, 87° 36’ 32”
West.
The first two specimens shown below were collected in
the late 1990s by an Empire Iron Mine employee. The next four samples
were collected in the late 1980s by the Potomac Museum Group (Minneapolis,
Minnesota, USA).
What does Grypania represent? The safest
identification is that they are eucaryotes (Domain Eucaryota). In a
generalized way, they are often simply referred to as fossil algae.
Grypania spiralis (or Grypania cf. Grypania spiralis)
- several specimens in gray, finely-laminated, iron-rich mudshale from the
Negaunee Iron-Formation of Ishpeming, UP of Michigan, USA. The largest
specimen (at lower right) is about 2.4 cm at its widest.
Grypania spiralis ribbons on reddish-brown, finely-laminated
taconite. The large fossil ribbon fragment at left is about 1 mm wide.
Grypania spiralis ribbons on gray, finely-laminated, iron-rich mudshale
(slab is 9.0 cm across). Each fossil ribbon is ~0.5 to 0.6 mm wide.
Grypania spiralis ribbon on taconitic mudshale, 2.5 cm across at its
widest. Ribbon is ~0.6 mm wide.
Grypania spiralis ribbons on taconite (field of view ~5.4 cm across).
Grypania spiralis ribbons on finely-laminated taconitic mudshale (field
of view ~2.9 cm across).
Grypania spiralis from the 2.11 b.y. (or 1.874 b.y.) Negaunee
Iron-Formation at the Empire Mine, Negaunee, Upper Peninsula of Michiga, USA
(FMNH PP 45972, Field Museum of Natural History, Chicago, Illinois, USA).