Rick Scoggin, Age 12, Of Scottsburg, Ore., for his question:
What was North America like in the Mesozoic era?
The age old story of the earth dates back more than 4 billion years, and the age old story of life dates back some 2 billion years. Geologists divide the unfolding record of lffe into five eras, like the chapters in a story book. The fourth chapter was the mesozoic era.
If we could go back to the start of the mesozoic era, we might think we had landed on another planet. Certainly we would not recognize our north america. But the great era spanned 125 million years, and during that time our land was reshaped" many times. The population of plants and animals also changed. As it ended some 60 million years ago, North America was very much like the land a re know today.
When the Mesozoic era opened, North and South America were separated by an aim of the sea. Volcanoes seethed among the eastern Appalachians, and there were no mountains in the west. The western picture changed as the Sierra Nevadas arose, taking millions of years to reach their full height. Later, the California region was cut off from North America by an invading arm of the sea. The most stupendous changes in the map of North America were made during the last 60 million years of the Mesozoic era. The western Rockies arose, and to the south the Panama Ridge lifted from the sea and linked hands with the two Americas. Meantime the Arctic Ocean reached down and joined its waters with the gulf of Mexico, and for a while the central half of North America was submerged. When the Mosozoic era ended, the map of North America had been remodeled into its present shape.
The climate through the era changed slowly from arid to semiarid and finally to a long spell of warmth and moisture. The early plants were scrubby bushes, cycads and conifers. Ginkgos flourished in the northwest and huge monkey puzzle trees in the southwest. The forested regions were strewn with mosses, ferns and lichens. As the climate became warm and wet, the plant life grew rich and lush, and before the long era ended the world's first flowers had unfolded.
The dinosaurs were children of the Mesozoic, for their long reign began and ended in this era. Countless varieties of reptile came and went. Reptile type birds took to the air, and reptile monsters dominated the land and sea. They departed suddenly as the era closed, and the land was ready for the little mammals to unfold their story.
Geologists divide the long Mesozoic era into three periods. We would not recognize the North America that existed during the Triassic period or during the Jurassic period that followed it. We would see familiar signs in the early Cretaceous period, and before this final period was over the scenery of North America was very much like the land in which we live.