GEG-1 Lecture Notes - Lecture 3: Australian Shield, Metamorphic Rock, Igneous Rock
Document Summary
Began when the earth was formed about 4 600 000 000 years ago. Lasted for about 4 billion years, approximately 87% of earth"s history. Many cycles of mountain building and erosion took place. Precambrian shields, such as the canadian shield, brazilian shield, african shield, and. Shields of precambrian rock form the core areas" of all the continents. They are called shields because they tend to have the domed shape of a warrior"s. The centre of the canadian shield, however, is lower than its outer rim shield. First single-celled and multi-celled organisms are formed. The only part of canada that existed was the canadian shield buckle in a process called folding open, also contributed to the formation of these mountains. Now, most parts of the shield are less than 500 m high. At time, the peaks of this shield were as high as 12 000 m above sea level. These mountains were taller than any that exist today.
