Acasta gneiss
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The Acasta gneisses, located near Canada's Great Slave Lake, are among the oldest known rocks on Earth, with ages established radiometrically between 4.0 and 3.9 billion years. These granitic gneisses contain a relict zircon crystal dated to 4.2 billion years ago, suggesting it formed from granitic magma. It is believed they originated from older basaltic material that underwent melting and remelting due to tectonic processes. The Archean Eon, which began around 4 billion years ago, is characterized by the formation of Earth's crust and the emergence of early life forms.12
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Archean Eonā¦oldest rocks are the 4-billion-year-old Acasta granitic gneisses in northwestern Canada, and a single relict zircon grain dated to 4.2 billion years ago was found within these gneisses. Other ancient sediments and lavas occur in the 3.85-billion-year-old Isua belt of western Greenland (which is similar to an accretionary wedge inā¦
Read Moreā¦oldest rocks are the 4-billion-year-old Acasta granitic gneisses in northwestern Canada, and a single relict zircon grain dated to 4.2 billion years ago was found within these gneisses. Other ancient sediments and lavas occur in the 3.85-billion-year-old Isua belt of western Greenland (which is similar to an accretionary wedge inā¦
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North America4.6 to 3.0 billion years agoā¦uranium-lead technique revealed that the Acasta gneisses, which occur southeast of Great Bear Lake in the northwestern corner of the shield, were at least 3.8 billion (and possibly up to 3.96 billion) years old. In the northeastern part of the shield, rocks as old as 3.8 billion years are foundā¦
Read Moreā¦uranium-lead technique revealed that the Acasta gneisses, which occur southeast of Great Bear Lake in the northwestern corner of the shield, were at least 3.8 billion (and possibly up to 3.96 billion) years old. In the northeastern part of the shield, rocks as old as 3.8 billion years are foundā¦
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