Ancient rocks are exposed in several locations in North America and Greenland. The oldest rocks thus far recovered are the Acasta Gneisses from near Great Slave Lake. These highly metamorphosed rocks are dated at 4,030 Ma. More critical to our Story of Life are the ancient supracrustal rocks of Isua and Akilia, West Greenland, dated between 3,800 and 3,700 Ma. The ‘supracrustal’ tag denotes that these metamorphosed rocks were originally deposited as sediments or volcanic flows in shallow water. Similar ancient gneisses are known from upriver in the Minnesota River Valley, near the towns of Morton and Montevideo.
The Isua and Akilia rocks have become chapter one in the Story of Life. Some researchers have claimed that the ratio of two isotopes of carbon—the common form with six neutrons and a less common form with seven neutrons—demonstrate that life processes were occurring in the ocean at the time the original rock was deposited. These claims have been disputed by others who claim that the carbon isotope ratio is better explained by deep Earth processes during the pressure cooking of the rocks.
The samples in the display contain grey globules of metamorphosed carbon (graphite), the same material in pencil lead. These seams that may or may not hold the clues for the earliest life recorded on planet Earth.
Quick Links to: Introduction Oldest Rocks on Earth Oldest Fossils Prokaryotes vs. Eukaryotes Oldest Eukaryotes Oxygenation of the Atmosphere Ediacaran Fauna Snowball Earth Oldest Skeletons Pre-Cambrian/Cambrian Boundary Links for more information
