![]() ![]() Younger Proterozoic (Neoproterozoic) fossils have been found at a half-dozen parks, including Appalachian National Scenic Trail, Boston Harbor Islands National Recreation Area, Death Valley National Park, Grand Canyon National Park, Mojave National Preserve, and Yukon–Charley Rivers National Preserve. The stromatolites of Glacier National Park are some of the best-known examples of these fossils. Younger Mesoproterozoic fossils have been found at Grand Canyon National Park and Tonto National Monument. The oldest fossils in National Park Service areas are from the middle Proterozoic (Mesoproterozoic) and consist of microfossils, small macroscopic body fossils, and microbial structures from Glacier National Park, providing evidence of life from between about 1.5 and 1.4 billion years ago. The most famous examples are the soft-bodied organisms that made up the “Ediacaran biota”, named after the Ediacara Hills, an area in southern Australia where these organisms flourished between about 560 and 550 million years ago. Many forms of life evolved and then went extinct, leaving almost everything about them a complete mystery. Stromatolites and other trace fossils of microbes are joined by microfossils, rare body fossils of multicellular organisms, and trace fossils of moving creatures as life diversified. Proterozoic fossils are much more common and diverse than Archean fossils. Grand Canyon National Park, Glacier National Park, and Rocky Mountain National Park are notable examples. Clusters of parks with Proterozoic rocks are found in several areas (particularly the Mojave Desert, the Great Lakes, and the Blue Ridge and Piedmont regions), but many other parks also have Proterozoic rocks. A common type of metamorphosed sedimentary rock of the Proterozoic is quartzite, which began as sandstone. Sedimentary rocks of this age are frequently metamorphosed, but some are unaltered, particularly upper Proterozoic sandstone and conglomerate. Most of the rocks are metamorphic rocks such as schist and gneiss, or igneous rocks such as basalt and granite. You can find Proterozoic rocks at more than 60 NPS sites. Increasing oxygen had profound effects, including the triggering of ice ages, the creation of iron deposits, and the adaptation of some lifeforms to use oxygen, which led to complex multicellular life. Oxygen became an important component of the atmosphere, having been produced by early life as a waste product. At several times, vast amounts of ice formed, leading to ice ages. Instead, braided streams were more common. Land plants did not yet exist, so wind was much more effective at transporting sediment, and meandering streams were much less common without the support of vegetation. Erosion of the mountains provided sediment to nearby basins and shallow seas. Mountain ranges grew where landmasses collided. This rifting appears to have been stopped by the counteracting force of a continental collision on what is now the east coast of the continent. The rocks that formed at this time are best seen around Lake Superior. North America nearly rifted through what is now its midsection about 1.1 billion years ago. The opposite also happened, leading to continental rifting. During the Proterozoic Eon, modern plate tectonics became active, and the ancient cores of the continents moved over wide areas of the globe, accumulating smaller fragments of crust and sometimes colliding with other large landmasses. ![]() It accounts for a little less than 4/9ths of geologic time. It is also the longest geologic eon, beginning 2.5 billion years ago and ending 541 million years ago. ![]() The Proterozoic Eon is the most recent division of the Precambrian. Precambrian age stromatolite fossils, Glacier National Park, Montana. ![]()
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