Archeozoic Era
Archeozoic Era
The Archeozoic Era stretches from about 3.8 billion to 2.5 billion years ago. Traditionally, the beginning of the Archean is defined to coincide with the oldest rocks discovered. As recent discoveries have pushed back the earliest dated rocks to about 4.0 billion years old, the beginning of the Archean has also been pushed back correspondingly. However, most texts still continue to date the beginning to 3.8 billion years ago.
As the Late Heavy Bombardment (LHB) ended with the Hadean, the newly forming crust continued to stabilize, and eventually led to the creation of the continents. When the continents first appeared is still under debate. The Earth in this period was moderately warm. Although the sun was about 30% cooler than it is today, the geological activity of the earth was much higher, leading to a somewhat temperate climate. Most of the earth was covered with oceans. The atmosphere contained mostly methane and little to no oxygen; therefore it is considered a reducing atmosphere.
Although recent discoveries may change this view, it is generally believed that life first evolved in the Archean. Some of the oldest fossils of life on Earth include the Apex Chert (3.465 billion years old) and stromatolites (3.45 billion years old) from Australia, and the Swaziland microfossils from Africa (also about 3.45 billion years old). Dating the oldest life forms is difficult. Stromatolite-like structures have been shown to be as old as 3.5 billion years, but it can be debated whether they were made by living organisms, or natural forces (hydrothermal vents). The earliest conclusive radiometric markers of life (such as O-12 uptake, or the first evidence of photosynthesis, for example), date to about 2.7 billion years old. However, it is widely believed that the first life appeared much earlier, possibly around the beginning of the Archean, around 3.8 billion years ago, or even in the Hadean. The earliest chemical markers of life are dated to about 3.8
The Archeozoic Era stretches from about 3.8 billion to 2.5 billion years ago. Traditionally, the beginning of the Archean is defined to coincide with the oldest rocks discovered. As recent discoveries have pushed back the earliest dated rocks to about 4.0 billion years old, the beginning of the Archean has also been pushed back correspondingly. However, most texts still continue to date the beginning to 3.8 billion years ago.
As the Late Heavy Bombardment (LHB) ended with the Hadean, the newly forming crust continued to stabilize, and eventually led to the creation of the continents. When the continents first appeared is still under debate. The Earth in this period was moderately warm. Although the sun was about 30% cooler than it is today, the geological activity of the earth was much higher, leading to a somewhat temperate climate. Most of the earth was covered with oceans. The atmosphere contained mostly methane and little to no oxygen; therefore it is considered a reducing atmosphere.
Although recent discoveries may change this view, it is generally believed that life first evolved in the Archean. Some of the oldest fossils of life on Earth include the Apex Chert (3.465 billion years old) and stromatolites (3.45 billion years old) from Australia, and the Swaziland microfossils from Africa (also about 3.45 billion years old). Dating the oldest life forms is difficult. Stromatolite-like structures have been shown to be as old as 3.5 billion years, but it can be debated whether they were made by living organisms, or natural forces (hydrothermal vents). The earliest conclusive radiometric markers of life (such as O-12 uptake, or the first evidence of photosynthesis, for example), date to about 2.7 billion years old. However, it is widely believed that the first life appeared much earlier, possibly around the beginning of the Archean, around 3.8 billion years ago, or even in the Hadean. The earliest chemical markers of life are dated to about 3.8