The Precambrian was the "Age of Early Life." During the Precambrian, continents formed and our modern atmosphere developed, while early life evolved and flourished. Soft-bodied creatures like worms and jellyfish lived in the world's oceans, but the land remained barren. Common Precambrian fossils include stromatolites and similar structures, which are traces of mats of algae-like microorganisms, and microfossils of other microorganisms.
National parks that contain Precambrian rocks are special places because they reveal an ancient world where continents formed and early life developed. The oldest rocks exposed in the NPS are found in the Greater Yellowstone parks of Bighorn Canyon, Grand Teton, and Yellowstone, and contain evidence of events as much as 3.6 billion years old. Ancient Precambrian rocks of the Canadian Shield are exposed in Voyageurs National Park. The 1,400-million-year-old stromatolites of Glacier National Park are among the oldest fossils in the NPS. The 1,100-million year-old rocks of Shenandoah National Park represent molten materials emplaced during the rise and fall of a Precambrian mountain range.
The Precambrian is divided into three eons highlighted below, from youngest to oldest: Hadean, Archean, and Proterozoic. A few examples of NPS resources in each time Period are highlighted below.
The Hadean Eon began with the formation of the first rocks on Earth and ended 4 billion years ago. This eon was a time of massive volcanic activity and frequent collisions with asteroids, leading to rapid changes of the planet’s surface. Because of the extreme changes and the great age of the rocks involved, very little evidence of the events of the Hadean Eon has survived to the present day. The oldest rocks and minerals are found in the Canadian Shield and western Australia. None of the lands included in the National Park Service are known to preserve any rocks or minerals from the Hadean Eon.
The Archean Eon began 4 billion years ago and ended 2.5 billion years ago. During this time, the first areas of continental crust appeared and began coalescing into larger landmasses. These continental cores are known as cratons or shields. Collisions with objects from space and volcanic activity decreased. Life first appeared on Earth during the Archean Eon. The earliest types of fossils to be found in any quantity are traces of microbial mats. A mat of aquatic microbes would trap sediment, and the microbes would grow over the sediment, producing a layered structure. Stromatolites are one well-known type of microbial mat fossil. None of the lands in the National Park Service have Archean fossils, but a handful have rocks this old. They are concentrated in two general areas: southern Idaho into northwestern Wyoming (Bighorn Canyon National Recreation Area, City of Rocks National Reserve, Grand Teton National Park, and Yellowstone National Park) and northeastern Minnesota into Wisconsin (Ice Age National Scenic Trail, Saint Croix National Scenic River, and Voyageurs National Park). The Archean rocks in these parks all appear to have formed late in the eon, between about 3 and 2.5 billion years ago.
Prehistoric Life Coloring Book
Every park contains some slice of geologic time. Below, we highlight selected parks associated with the Precambrian. This is not to say that a particular park has only rocks from the specified period. Rather, rocks in selected parks exemplify a certain event or preserve fossils or rocks from a certain geologic age.