Precambrian+Era

Precambrian Era
media type="custom" key="21737812" The earth was formed about 4 600 000 000 years ago. The Precambrian era began at this time and lasted for about 4 000 000 000 years, approximately 87% of the earth's history. Many cycles of mountain building and erosion took place during this era. During the Precambrian era, the only part of Canada that existed was the Canadian Shield. At times, the peaks of the Canadian Shield were as high as 12 000 m above sea level. These enormous mountains were taller than any that exist today.

 The uplifting was accomplished as enormous pressure caused the earth to buckle in a process called folding. Other processes such as volcanic action and faulting, in which the earth cracks open, also contributed to the formation of these mountain. Over millions of years, these mountains were gradually eroded only to be replaced by new mountains. Areas of land and ocean developed and then disappeared many times.

 The rest of Canada, as we know it, did not even form until hundreds of millions of years later. The Canadian Shield is the largest landform region in Canada and the other regions have formed around it. The Shield consists mainly of igneous and metamorphic rock and some sedimentary rock. Igneous rock is created when hot, melted magma rises from deep under the earth's crust, then cools and hardens. Igneous rock can either be changed directly into metamorphic rock or break down into particles or sediments that harden into sedimentary rock. When pressure and heat melt the sedimentary rock, the result is also metamorphic rock.

 There are fossils in the Shield dating back to the middle of the Precambrian era. These are the remains of material deposited by algae, the first single-celled organisms. By the end of this era, more complex organisms had developed.

 1. "The earth's physical landscape is the result of conflict between forces..." Explain what you think this means.

 2. a) What part of Canada was created during the Precambrian era?  b) What types of rocks make up this landform?  c) How did it differ in appearance from today?

3. Explain how each of the three types of rock are formed.