Archaean
Published: August 29, 2008, 2:30 pm
Updated: August 29, 2008, 2:30 pm
This article has been reviewed by the following Topic Editor:
Mark McGinley Introduction
If you were able to travel back to visit the Earth during the Archaean, you would likely not recognize it is the same planet we inhabit today. The atmosphere was very different from what we breathe today; at that time, it was likely a reducing atmosphere of methane, ammonia, and other gases which would be toxic to most life on our planet today. Also during this time, the Earth's crust cooled enough that rocks and continental plates began to form.
It was early in the Archaean that life first appeared on Earth. Our oldest fossils date to roughly 3.5 billion years ago, and consist of bacteria microfossils. In fact, all life during the more than one billion years of the Archaean was bacterial. At left is an artist's depiction of what an Archaean coast might have looked like 3.5 billion years ago. The mounds in the foreground are stromatolites, colonies of photosynthetic bacteria which have been found as fossils in Early Archaean rocks of South Africa and Western Australia. Stromatolites increased in abundance throughout the Archaean, but began to decline during the Proterozoic. They are not common today.
Subdivision of the Archaean
The chart at right shows the three major subdivisions of the Archaean. These divisions are somewhat arbitrary, and we have not attempted to prepare exhibits on each of them. Dates and divisions follow those of Schopf.
The Archaean occurs between the Hadean and the Proterozoic.
Further Reading
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Citation
University of California Museum of Paleontology (Lead Author);Mark McGinley (Topic Editor) "Archaean". In: Encyclopedia of Earth. Eds. Cutler J. Cleveland (Washington, D.C.: Environmental Information Coalition, National Council for Science and the Environment). [First published in the Encyclopedia of Earth August 29, 2008; Last revised Date August 29, 2008; Retrieved May 21, 2013 <http://www.eoearth.org/article/Archaean>
The Author
The mission of the University of California Museum of Paleontology (UCMP) is to investigate and promote the understanding of the history of life and the diversity of the Earth's biota through research and education. UCMP is an active center of national and international research and houses one of the nation's largest collections of fossils as well as state-of-the-art facilities for the study of these fossils.
UCMP has the largest paleontological collection of any university museum in the world. ... (Full Bio)
Introduction
If you were able to travel back to visit the Earth during the Archaean, you would likely not recognize it is the same planet we inhabit today. The atmosphere was very different from what we breathe today; at that time, it was likely a reducing atmosphere of methane, ammonia, and other gases which would be toxic to most life on our planet today. Also during this time, the Earth's crust cooled enough that rocks and continental plates began to form.
It was early in the Archaean that life first appeared on Earth. Our oldest fossils date to roughly 3.5 billion years ago, and consist of bacteria microfossils. In fact, all life during the more than one billion years of the Archaean was bacterial. At left is an artist's depiction of what an Archaean coast might have looked like 3.5 billion years ago. The mounds in the foreground are stromatolites, colonies of photosynthetic bacteria which have been found as fossils in Early Archaean rocks of South Africa and Western Australia. Stromatolites increased in abundance throughout the Archaean, but began to decline during the Proterozoic. They are not common today.
Subdivision of the Archaean
The chart at right shows the three major subdivisions of the Archaean. These divisions are somewhat arbitrary, and we have not attempted to prepare exhibits on each of them. Dates and divisions follow those of Schopf.
The Archaean occurs between the Hadean and the Proterozoic.
Further Reading
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Artist's depiction of what an Archaean coast might have looked like 3.5 billion years ago. (Source: University of California Museum of Paleontology)
Three major subdivisions of the Archaean. (Source: University of California Museum of Paleontology)
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