Precambrian Eonothem
Quick Summary
The Precambrian Eonothem represents the earliest span of Earth's history, encompassing the Archean and Proterozoic Eons, from approximately 4.6 billion to 541 million years ago. This vast period is characterized by significant geological events, including the growth of Earth's crust and the formation of early continents.123
Key features of the Precambrian include:
* Subdivisions: The Archean Eon (4.0 to 2.5 billion years ago) and the Proterozoic Eon (2.5 billion to 541 million years ago).1
* Rock Formations: Unique rock types like banded-iron formations and komatiite, which are rare in later geological periods.3
* Mineral Deposits: The formation of many of the world's valuable mineral deposits, such as gold, nickel, and iron.34
* Early Life: Evidence of primitive life-forms, including bacteria, blue-green algae, and early animals like the Ediacara fauna.4
* Atmospheric Changes: A significant increase in atmospheric oxygen due to photosynthesis.4
Stratigraphy during the Precambrian relies on field relationships and isotopic dating due to the scarcity of fossils. The oldest known minerals and rocks on Earth date back to this eon.156
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AfricaThe PrecambrianThe oldest rocks consist of gneisses, granites, metasediments, and metavolcanic rocks 3.6 to 2.5 billion years old; all are variably deformed and metamorphosed to some degree. The best-preserved assemblages occur in the Kaapvaal and Zimbabwe cratons and contain large deposits of gold and sulfideā¦
Read MoreThe oldest rocks consist of gneisses, granites, metasediments, and metavolcanic rocks 3.6 to 2.5 billion years old; all are variably deformed and metamorphosed to some degree. The best-preserved assemblages occur in the Kaapvaal and Zimbabwe cratons and contain large deposits of gold and sulfideā¦
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AsiaThe PrecambrianThe recorded history of the Precambrian, which covers more than 80 percent of Earthās geologic history, is divided into two eons: the Archean, between roughly 4 and 2.5 billion years ago, and the Proterozoic, between 2.5 billion and 541 million years ago. In Asiaā¦
Read MoreThe recorded history of the Precambrian, which covers more than 80 percent of Earthās geologic history, is divided into two eons: the Archean, between roughly 4 and 2.5 billion years ago, and the Proterozoic, between 2.5 billion and 541 million years ago. In Asiaā¦
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AustraliaTectonic frameworkPrecambrian rocks occupy three tectonic environments. The first is in shields, such as the Yilgarn and Pilbara blocks of the Western Shield, enclosed by later orogenic (mountain) belts. The second is as the basement to a younger cover of Phanerozoic sediment (deposited during the pastā¦
Read MorePrecambrian rocks occupy three tectonic environments. The first is in shields, such as the Yilgarn and Pilbara blocks of the Western Shield, enclosed by later orogenic (mountain) belts. The second is as the basement to a younger cover of Phanerozoic sediment (deposited during the pastā¦
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Canadian Shieldā¦the largest mass of exposed Precambrian rock on the face of Earth. The region, as a whole, is composed of ancient crystalline rocks whose complex structure attests to a long history of uplift and depression, mountain building (orogeny), and erosion. Some of the ancient mountain ranges can still be recognizedā¦
Read Moreā¦the largest mass of exposed Precambrian rock on the face of Earth. The region, as a whole, is composed of ancient crystalline rocks whose complex structure attests to a long history of uplift and depression, mountain building (orogeny), and erosion. Some of the ancient mountain ranges can still be recognizedā¦
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EuropePrecambrianCompared with most of the other continents, Europe has few exposed rocks from Precambrian time (subdivided into the older Archean and the younger Proterozoic eons). Some granitic gneisses, which are more than 3 billion years old, crop out in the northern Baltic Shield, theā¦
Read MoreCompared with most of the other continents, Europe has few exposed rocks from Precambrian time (subdivided into the older Archean and the younger Proterozoic eons). Some granitic gneisses, which are more than 3 billion years old, crop out in the northern Baltic Shield, theā¦
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South AmericaThe PrecambrianPrecambrian rocks constitute the oldest rocks of the continent and are preserved in the five core cratons. Those rocks are represented by high- to low-grade metamorphosed assemblages along heavily deformed belts of plutonic (intrusive), metavolcanic (metamorphosed extrusive igneous rocks), and metasedimentary rocks. Rocks ofā¦
Read MorePrecambrian rocks constitute the oldest rocks of the continent and are preserved in the five core cratons. Those rocks are represented by high- to low-grade metamorphosed assemblages along heavily deformed belts of plutonic (intrusive), metavolcanic (metamorphosed extrusive igneous rocks), and metasedimentary rocks. Rocks ofā¦
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