The Archean
The Archean is the name of the age which began with the forming Earth. The duration of the Archean, 2.8 billion years, is more than half the expected age of the Earth. We don't know much about this period, yet some of the most dramatic changes in Earth's history took place. Especially when compared to the changes taking place on other planets at this time. For example, in the same period of time Mars was already a frozen ball with no life and no ocean. . So many things happened that is it hard to describe everything in one page, so try the Exploratour on The Archean Age, found at the bottom of this page. At the beginning of the age, the "birth" of the Earth, at 4.8 BYA (billion years ago) the Sun finished it's T-Tauri phase and blew away whatever atmosphere the Earth started with, and Earth started over with an atmosphere of hydrogen dominated components (a "reducing" atmosphere). Also the Earth
differentiated.
Temperatures were too hot for a liquid water ocean to condense. Igneous rocks dominated the surface, and there was volcanic activity which yielded new molecules for the atmosphere.
As the temperature fell to condensation temperatures for water, liquid water condensed on the surface and created a vast ocean. As sizeable pools of liquid water formed, carbon and sulfur dioxide from the atmosphere dissolved into the water, removing large quanities of those elements from the atmosphere (this is in contrast to Mars or Jupiter where CO2 and H continue to dominate the atmospheres of those respective planets). Nitrogen began to build up in the atmosphere. Volcanic activity continued to pour forth a
secondary atmosphere for the Earth. Meanwhile the seeds of continents called the "continental shields" began to take shape.
By 3.8 BYA (a billion years later) the first living beings are believed to have been thriving. These beings were able to thrive in an anaerobic environment, that is one without oxygen. Some of these creatures, called Archaea, bear the name of the entire age. Waste products of sulfur from these living beings began accumulating in the ocean, as well as the products of the weathering of igneous rock such as Fe2+. The build up of these waste products gradually changed the oxidation state of the ocean.
From 3.5 BYA to 2.5 BYA, or roughly to the end of the Archean age, iron ores began to be deposited in large amounts at the bottom of the ocean. This is significant because it is proof that oxygen was beginning to be formed by the first living beings. The excess oxygen first combined with excess Fe2+ to form Fe2O3 otherwise known as iron ore. This process took one billion years and finished at the end of the Archean era.
