Samarium radioactive dating
The oldest known rocks—the faux amphibolites of the Nuvvuagittuq greenstone belt in Quebec, Canada—however, have an isotopic age of 4.28 billion years.There is in effect a stretch of approximately 300 million years for which no geologic record for rocks exists, and the evolution of this pregeologic period of time is, not surprisingly, the subject of much speculation.Carbon monoxide, carbon dioxide, water vapour, and methane predominated; however, free oxygen could not have been present, since even modern volcanic gases contain no oxygen.It is therefore assumed that the secondary atmosphere during the Archean Eon (4 billion to 2.5 billion years ago) was anoxygenic.Particles in the solar nebula condensed to form solid grains, and with increasing electrostatic and gravitational influences they eventually clumped together into fragments or chunks of rock. The constituent metallic elements sank toward the centre of the mass, while lighter elements rose toward the top.
These models place Earth’s age at approximately 4.5 billion years old.
This mineral is the oldest dated material on Earth.
The rocks from which the zircons in the quartzites and conglomerates were derived have either disappeared or have not yet been found.
Its component gases, however, were most likely very different from those emitted by modern volcanoes.
Accordingly, the composition of the early secondary atmosphere was quite distinct from that of today’s atmosphere.