Life May Have Created the Continents |
|
Written by spacetravel.org
|
|
Sunday, 26 March 2006 14:12 |
|
Researchers led by Minik Rosing of the Geological Museum and the Nordic Centre for Earth Evolution at the University of Copenhagen, Denmark believe that the appearance of photosynthetic life may have led to the creation of the Earths continental crust.
The Earth formed 4.6 billion years ago. However, during the first 600 to 800 million years, there were no stable continents. The oldest vestiges of continental crust date from about 4 billion years ago. They are found in Acasta in northwest Canada, and are made from granite, or a similar material, which is unique to Earth. It is created when basalt rock melts and reforms, becoming enriched in silica, aluminium and certain metals as it reacts with compounds in water. Because granitic rocks are less dense than basalt, they rise to the surface, creating a stable continental crust.
Rosings team noticed that the continental crust appeared at the time of the rise of photosynthesis. By making solar energy available for life changes, the first photosynthetic life forms would have cranked up Earths energy cycle and altered its geochemistry. Rosings team believes that the energy capture from photosynthesis is used to keep oceans and atmosphere out of chemical equilibrium with the rock. The tension would enhance weathering cycles, causing more chemical breakdown in the crust compared with physical processes or with the limited impact of obscure organisms, such as microbes that live around thermal vents. The breakdown of basalt would produce smectite and illite clays, which play a role in the creation of granite.
|