THE SEED-PLANT PERIOD
THE AGE OF BIOLOGIC TRIBULATION
This period marks the end of pivotal evolutionary development in marine life and the opening of the transition period leading to the subsequent ages of land animals.
This age was one of great life impoverishment. Thousands of marine species perished, and life was hardly yet established on land. This was a time of biologic tribulation, the age when life nearly vanished from the face of the earth and from the depths of the oceans. Toward the close of the long marine life era there were more than one hundred thousand species of living things on earth. At the close of this period of transition less than five hundred had survived.
The peculiarities of this new period were not due so much to the cooling of the earth’s crust or to the long absence of volcanic action as to an unusual combination of commonplace and pre-existing influences – restrictions of the seas and increasing elevation of enormous land masses. The mild marine climate of former times was disappearing, and the harsher continental type of weather was fast developing.
170,000,000 years ago, great evolutionary changes and adjustments were taking place over the entire face of the earth. Land was rising all over the world as the ocean beds were sinking. Isolated mountain ridges appeared. The eastern part of North America was high above the sea; the west was slowly rising. The continents were covered by great and small salt lakes and numerous inland seas which were connected with the oceans by narrow straits. The strata of this transition period vary in thickness from 1,000 to 7,000 feet.
The earth’s crust folded extensively during these land elevations. This was a time of continental emergence except for the disappearance of certain land bridges, including the continents which had so long connected South America with Africa and North America with Europe. Gradually the inland lakes and seas were drying up all over the world. Isolated mountain and regional glaciers began to appear, especially over the Southern Hemisphere, and in many regions the glacial deposit of these local ice formations may be found even among some of the upper and later coal deposits. Two new climatic factors appeared – glaciation and aridity. Many of the earth’s higher regions had become arid and barren.
Throughout these times of climatic change, great variations also occurred in the land plants. The seed plants first appeared, and they afforded a better food supply for the subsequently increased land-animal life. The insects underwent a radical change. The resting stages evolved to meet the demands of suspended animation during winter and drought.
Among the land animals the frogs reached their climax in the preceding age and rapidly declined, but they survived because they could long live even in the drying-up pools and ponds of these far-distant and extremely trying times. During this declining frog age, in Africa, the first step in the evolution of the frog into the reptile occurred. And since the land masses were still connected, this prereptilian creature, an air breather, spread over all the world. By this time the atmosphere had been so changed that it served admirably to support animal respiration. It was soon after the arrival of these prereptilian frogs that North America was temporarily isolated, cut off from Europe, Asia, and South America.
The gradual cooling of the ocean waters contributed much to the destruction of oceanic life. The marine animals of those ages took temporary refuge in three favorable retreats: the present Gulf of Mexico region, the Ganges Bay of India, and Sicilian Bay of the Mediterranean basin. And it was from these three regions that the new marine species, born to adversity, later went forth to replenish the seas.
160,000,000 years ago, the land was largely covered with vegetation adapted to support land-animal life, and the atmosphere had become ideal for animal respiration. Thus, ends the period of marine-life curtailment and those testing times of biologic adversity which eliminated all forms of life except such as had survival value, and which were therefore entitled to function as the ancestors of the more rapidly developing and highly differentiated life of the ensuing ages of planetary evolution.
The ending of this period of biologic tribulation, known to our students as the Permian, also marks the end of the long Paleozoic era, which covers one quarter of the planetary history, two hundred and fifty million years.
The vast oceanic nursery of life on Urantia has served its purpose. During the long ages when the land was unsuited to support life, before the atmosphere contained sufficient oxygen to sustain the higher land animals, the sea mothered and nurtured the early life of the realm. Now the biologic importance of the sea progressively diminishes as the second stage of evolution begins to unfold on the land.