The vast group of rock systems which constituted the outer crust of the world during the life-dawn or Proterozoic era does not now appear at many points on the earth’s surface. And when it does emerge from below all the accumulations of subsequent ages, there will be found only the fossil remains of vegetable and early primitive animal life. Some of these older water-deposited rocks are commingled with subsequent layers, and sometimes they yield fossil remains of some of the earlier forms of vegetable life, while on the topmost layers occasionally may be found some of the more primitive forms of the early marine-animal organisms. In many places, these oldest stratified rock layers, bearing the fossils of the early marine life, both animal and vegetable, may be found directly on top of the older undifferentiated stone.
Fossils of this era yield algae, coral like plants, primitive Protozoa, and spongelike transition organisms. But the absence of such fossils in the early rock layers does not necessarily prove that living things were not elsewhere in existence at the time of their deposition. Life was sparse throughout these early times and only slowly made its way over the face of earth.
The rocks of this olden age are now at the earth’s surface, or very near the surface, over about one eighth of the present land area. The average thickness of this transition stone, the oldest stratified rock layers, is about one and one-half miles. At some points, these ancient rock systems are as much as four miles thick, but many of the layers which have been ascribed to this era belong to later periods.
In North America, this ancient and primitive fossil-bearing stone layer comes to the surface over the eastern, central, and northern regions of Canada. There is also an intermittent east-west ridge of this rock which extends from Pennsylvania and the ancient Adirondack Mountains on west through Michigan, Wisconsin, and Minnesota. Other ridges run from Newfoundland to Alabama and from Alaska to Mexico.
The rocks in this era are exposed here and there all over the world, but none are so easy of interpretation as those about Lake Superior and in the Grand Canyon of the Colorado River, where these primitive fossil bearing rocks, existing in several layers, testify to the upheavals and surface fluctuations of those faraway times.
This stone layer, the oldest fossil-bearing stratum in the crust of the earth, has been crumpled, folded, and grotesquely twisted as a result of the upheavals of earthquakes and the early volcanoes. The lava flows of this age brought much iron, copper, and lead up near the planetary surface.
There are few places on earth where such activities are more graphically shown than in the St. Croix valley of Wisconsin. In this region, there occurred one hundred and twenty-seven successive lava flows on land with succeeding water submergence and consequent rock deposition. Although much of the upper rock sedimentation and intermittent lava flow is absent today, and though the bottom of this system is buried deep in the earth, nevertheless, about sixty-five or seventy of these records of past ages are now exposed to view.
In these early ages when much land was near sea level, there occurred many successive submergences and emergences. The earth’s crust was just entering upon its later period of comparative stabilization. The undulations, rises and dips, of the earlier continental drift contributed to the frequency of the periodic submergence of the great land masses.
During these times of primitive marine life, extensive areas of the continental shores sank beneath the seas from a few feet to half a mile. Much of the older sandstone and conglomerates represents the sedimentary accumulations of these ancient shores. The sedimentary rocks belonging to this early stratification rest directly upon those layers which date back far beyond the origin of life, back to the early appearance of the worldwide ocean.
Some of the upper layers of these transition rock deposits contain small amounts of shale or slate of dark colors, indicating the presence of organic carbon and testifying to the existence of the ancestors of those forms of plant life which overran the earth during the succeeding Carboniferous or coal age. Much of the copper in these rock layers results from water deposition.
Some is found in the cracks of the older rocks and is the concentrate of the sluggish swamp water of some ancient sheltered shore line. The iron mines of North America and Europe are located in deposits and extrusions lying partly in the older unstratified rocks and partly in these later stratified rocks of the transition periods of life formation.
The era witnesses the spread of life throughout the waters of the world; marine life has become well established on Urantia. The bottoms of the shallow and extensive inland seas are being gradually overrun by a profuse and luxuriant growth of vegetation, while the shore-line waters are swarming with the simple forms of animal life. Many of these ancient sea beds are now elevated high upon land, and their deposits of age upon age tell the story of the life struggles of those early days. It is literally true, as one of our poets has said, “The dust we tread upon was once alive.”
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