On the other hand, rocks containing these minerals may still exist on Earth’s surface but simply have not been found.
The age of these rocks was estimated using a radiometric dating technique that measures the ratio of the rare-earth elements neodymium and samarium present in a sample.
The Acasta gneisses, found near Canada’s Great Slave Lake, are also among the world’s oldest rocks.
Afterward, when such continents had emerged, orogenic belts were able to form on the margins of and between continental blocks. The first occurs in upper crustal greenstone-granite belts rich in volcanic rocks that are probably primitive types of oceanic crust and island arcs (long, curved island chains associated with intense volcanic and seismic activity) that formed during the early rapid stage of crustal growth.
The second occurs in granulite-gneiss belts that were recrystallized in the Archean mid-lower crust under metamorphic conditions associated with high-temperature granulite and amphibolite facies.
Observations on Settlement and Subsistence during the Late La Jolla Complex - Preceramic Interface as Evidenced at Site CA-SDI-11,796, Lower San Diego River Valley, San Diego County, California [SCA Proceedings - PDF].
Recovery, Synthesis, and Reporting: 1990s Anza-Borrego Desert State Park Cultural Resources Inventory Conducted by the Archaeological Research Unit, University of California, Riverside [California State Parks].There are several other rock types that developed primarily during the Precambrian but rarely later.This restriction is a result of the unique conditions that prevailed during Precambrian time.Comparisons with the Moon indicate that the Earth must have been subjected to an enormous number of meteorite impacts about 4 billion years ago, but there is no geologic evidence of such events.Nuvvuagittuq greenstone belt in Quebec, Canada; they are estimated to be 4.28 billion years old.The paucity of Precambrian fossils, however, precludes the creation of small-scale subdivisions (epochs and ages) in this time period.