Colorful Rocks of the Great Lakes 5

A combo plate of Archean Eon (4000–2500 million years ago) and Proterozoic Eon (2500–541 million years ago) stromatolites, stromatoporoids, and unakite, the latter a pink and green semiprecious stone common on Lake Michigan's Left Coast. Copyright, Disclaimer, Glossary, Bibliography


Colorful Rocks of the Great Lakes 4

In its earliest youth, our planet was molten, red-hot, and battered by abundant meteorites. Earth was so hostile to life that scientists named this period the Hadean Eon (4.6–4 billion years ago), for Hades, the Greek god of the place known as Hell. Life began to evolve after Earth settled down a bit, in the... Continue Reading →

Colorful Rocks of the Great Lakes 3

Banded Iron Formation (BIF) is a sedimentary rock, but because its extreme age, Archean BIF is highly metamorphosed. It has been compressed, "cooked," and shot through with veins of quartz and granite. The best source of BIF in the United States is north of my location on Lake Michigan. Lots of it was transported here... Continue Reading →

Colorful Rocks of the Great Lakes 2

Archean Eon (4 to 2.5 billion years ago) rocks are frequently deep-water sediments like Banded Iron Formation (BIF). Archean BIF is found in strata no younger than 2.5 billion years, making it one of the oldest rock-types on Earth. Northern Minnesota contains bountiful Archean BIF formations that have been mined for iron ore. Glaciers brought... Continue Reading →

Colorful Rocks of the Great Lakes 1

How lucky am I? Some of the oldest rocks on Earth lie north of my location on Lake Michigan. A half-dozen glacial waves carried rocks from the Precambrian exposures in the northern Great Lakes to my beach in southeastern Wisconsin. Characterized by stripes of red iron-oxide particles, these rocks are called Banded Iron Formation (BIF).... Continue Reading →

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