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The Fossil Record of Virginia
And the Mid-Atlantic Region
GRENVILLE; 570 - 490 mya
Part of the story of Virginia is the life which lived here in the past, but, because all the Grenville age rocks preserved in Virginia are igneous and metamorphic there are no fossils to be found for this time. If life was in Virginia during Grenville time it would live on the land surface above the igneous and metamorphic rocks. What would that life be like?
The oldest fossils on the earth are 3.5 billion year old simple bacteria from Australia. Bacteria are the only life forms until about 1.4 billion years ago. Then the first single celled organisms similar to green algae with a nucleus appeared. Not until about 650 million years ago did the first multicellular animals evolve.
During Grenville time the mountains of Virginia were a stark and barren landscape. In the streams and ponds may have been bacteria, some of it possibly brightly colored reds, blues, and greens. And on the rocks probably lichens. But no trees, no bushes, no low grass-like plants at all. And search as you might, not an animal anywhere. It is a world we who are used to abundant life all around would find strange, even discomforting.
MIDDLE CAMBRIAN AND LOWER ORDOVICIAN; 570 - 490 mya
During this time eastern North America lay in the tropics 20-300 south of the equator. Carbonate tidal flat deposits (limestones and dolomites) many thousands of feet thick accumulated. In the Ordovician the environments changed into shallow shelf environments, still carbonate dominated.
Great changes occurred in the history of life during these times. At the base of the Cambrian, at the time of Protoatlantic rifting, the first multicellular animals became common, and a fossil record which was very sparse suddenly becomes common. Trilobites, brachiopods, snails, and many other animals lived in the Cambrian seas. In Virginia the remains of these fossils are rare and hard to find. In the early Ordovician, however, a major revolution in life took place and after that fossils are common and readily seen in the rocks. This is especially so in the Lincolnshire formation where early reefs are found.