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Greenwood/Blue Lotus Press
> Fowler > science art
geology, astronomy, geography
click image to enlarge
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banded iron formation (BIF)
The photo was taken at a rock outcrop called Jasper
Knob in Ishpeming, Michigan (near Marquette in the upper
peninsula). This is an outcropping of the Negaunee Iron-Formation
which has been dated (Sm-Nd isotopes) at 2.1 billion
years. This places it in the Early Proterozoic (or Proterozoic
X in the USGS nomenclatures used on their maps).
The red bands are a red chert (micro-crystalline quartz)
often called 'jasper' and the blue-grey bands are mostly
hematite, with a good deal of the 'specular' variety
with its metallic luster (the kind of dull silvery hematite
that is used in jewelry).
The Negaunee Iron-Formation has been found to contain
fossils of Grypania spiralis (Han & Runnegar, 1992),
an early photosynthetic algae. Many of the iron-formations
in the Lake Superior region have yielded microfossils
of prokaryotic cyanobacteria, but the presence of Grypania
indicates eukaryotic cells as far back as 2.1 billion
years.
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star trails over the Appalachian
Trail, Berks County
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compass variations
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star map
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C 130
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C 130
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