tailieunhanh - Marine Geology Phần 2

Số lượng các chi của động vật thân mềm, brachiopods, và bọ ba thùy đáng kể tăng lên, bởi vì sinh vật với thức ăn dồi dào có nhiều khả năng phát triển mạnh và đa dạng hóa thành những loài khác nhau. | MARINE GEOLOgy pumped nutrients into the sea fueling booms of marine plankton which increased the food supply for higher creatures. The number of genera of mollusks brachiopods and trilobites dramatically increased because organisms with abundant food are more likely to thrive and diversify into different species. During the formation of Laurasia island arcs between the two landmasses were scooped up and plastered against continental edges as the oceanic crustal plate carrying the islands subducted under Baltica. This subduction rafted the islands into collision with the continent and deposited the formerly submerged rocks onto the present west coast of Norway. Slices of land called terranes residing in western Europe drifted into the Iapetus from ancient Africa. Likewise slivers of crust from Asia traveled across the ancestral Pacific Ocean called the Panthalassa to form much of western North America. North America was a lost continent around 500 million years ago. During that time the continental landmass and a few smaller continental fragments drifted freely on their own. South America Africa Australia Antarctica and India had assembled into Gondwana by continental plate collisions. At this time North America was situated a few thousand miles off the western coast of South America placing it on the western side of Gondwana. Eventually North and South America collided Fig. 15 placing what would be present-day Washington . near Lima Peru. A limestone formation in Argentina Figure 15 North and South America might have collided at the beginning of the Ordovician 500 million years ago. 20 THE BLUE PLANET contains a distinctive trilobite species typical of North America but not of South America suggesting the two continents once had much in common. THE PANTHALASSA SEA Throughout geologic history smaller continental blocks collided and merged into larger continents. Millions of years after assembling the continents rifted apart and the chasms filled with seawater to