Precambrian

Precambrian is an informal term used to describe the time interval between the formation of Earth at c. 4.56 Ga, a few million years after the emergence of the Solar System, and the beginning of the Cambrian Period at 541 Ma. Spanning almost 88% of the planet's history, this time interval has been divided according to major geological events recorded on Earth and encompasses the informal Hadean (4.56–4.0 Ga) and the formal Archean (4.0–2.5 Ga) and Proterozoic (2.5–0.541 Ga) eons. Due to the absent to poorly-preserved rock record and the lack of index fossils throughout most of its extent, the Precambrian is still less well known than the Phanerozoic. Nevertheless, recent scientific advances and the study of Precambrian units preserved in ancient cratons and adjacent areas have allowed remarkable progress in its understanding. The available information indicates that, after accretion from the Solar Nebula, the early Earth was dominated by extreme conditions and extreme impact rates that also induced the formation of the Moon. The primitive hydrosphere-atmosphere, the biosphere and an early magnetosphere emerged in this interval, under planetary tectonic modes similar to those observed on the Galilean moon Io and/or Venus. The early Archean onset in the secular cooling of the mantle was accompanied by the formation and preservation of remarkable volumes of unique continental crust types and the spread of shallow marine to continental sedimentary systems, which hosted some of the oldest well-known life forms and evolved under dominant anoxic atmospheric and oceanic conditions. Following a period dominated by plume activity and transient, hot shallow-dipping subduction systems, the Proterozoic was marked by the gradual emergence of plate tectonics and the onset of the supercontinent cycle. This eon witnessed the increasing maturity of sedimentary systems, extreme global climate changes, the shift in the genesis of major economic resources, the rise of photosynthetic organisms, eukaryotes, macroscopic life forms and the coupled evolution of the atmosphere, hydrosphere and biosphere. In the late Neoproterozoic, renewed plate reorganizations were accompanied by Snowball Earth glaciations, the emergence of metazoans and biomineralization processes, the complete oxygenation of oceans and atmosphere and the assembly of the 630–500 Ma Gondwana supercontinent (precursor of Wegener's Pangea). Although much is still to be done and understood, it is apparent that the foundations which made Earth a unique planet in the Solar System were built in the Precambrian. This time interval contains the roots of our ancestral history and offers a window into the early Earth and the deep time itself.