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The Proterozoic

• 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. Also the Earth differentiated.
• At first temperatures were very hot, so there was no ocean. Igneous rocks dominated the surface of the Earth, and there was a lot of volcanic activity which yielded new molecules for the atmosphere such as water vapor, carbon and sulfur dioxide.
• As the temperature fell to about room temperature, liquid water formed on the surface and created a vast ocean. As soon as water began to form on the surface, carbon and sulfur dioxide from the atmosphere dissolved into the water, removing elements from the Earth's atmosphere which we see in other planets, and 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. Some of these creatures, called Archaea, bear the name of the entire age. These beings did not require oxygen to survive, which is good since there was none in the atmosphere at this time. Waste products of sulfur from these living beings began gathering in the ocean, as well as the products of the breakdown of igneous rock such as iron.
• From 3.5 BYA to 2.5 BYA, or roughly to the end of the Archean age, iron ores began to be formed in large amounts at the bottom of the ocean. This is significant because it is proof that lots of oxygen was being formed by the first living beings. The excess oxygen first combined with excess iron to form Fe₂O₃ otherwise known as iron ore. This process took one billion years and fininshed at the end of the Archean era.

This drawing shows the Earth at the beginning of the Cambrian era. No one knows what the continents looked like in the Archean, nor whether there were any continents on the surface of the Earth.

Geologic Time Table

Exploratour: Life on Earth

The Proterozoic

• 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. Also the Earth differentiated.
• At first temperatures were very hot, so there was no ocean. Igneous rocks dominate the surface of the Earth, and there was a lot of volcanic activity which yielded new molecules for the atmosphere.
• As the temperature fell below to about room temperature, liquid water condensed on the surface and created a vast ocean. As soon as water began to form on the surface, 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. Some of these creatures, called Archaea, bear the name of the entire age. These beings did not require oxygen to survive, which is good since there was none in the atmosphere at this time. 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 Fe (iron).
• From 3.5 BYA to 2.5 BYA, or roughly to the end of the Archean age, iron ores began to be formed 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 Fe to form Fe₂O₃ otherwise known as iron ore. This process took one billion years and fininshed at the end of the Archean era.

This drawing shows the Earth at the beginning of the Cambrian era. No one knows what the continents looked like in the Archean, nor whether there were any continents on the surface of the Earth.

Exploratour: Life on Earth

The Proterozoic

• 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 fininshed at the end of the Archean era.

This drawing shows the Earth at the beginning of the Cambrian era. No one knows what the continents looked like in the Archean, nor whether there were any continents on the surface of the Earth.

Exploratour: Life on Earth

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