The Precambrian Climate

More than 88% of the history of the Earth occurred in the Precambrian. The Precambrian began with the formation of the Earth 4.6 billion years ago (Ga) and ended 542 million years ago (International Stratigraphic Chart, www.stratigraphy.org). It is subdivided into two large eons: the Archean (between 4 and 2.5 Ga) and the Proterozoic (from 2.5 to 0.542 Ga). The International Commission on Stratigraphy is proposing to add an extra eon, the Hadean, covering the first 600 million years of the history of our planet. Notwithstanding, this eon is described as having an informal status since no pre-Archean rock has been observed today. In fact, the oldest rocks date back to 4 billion years ago (U/Pb dating on zircon crystals). These are the Acasta gneisses in the Slave Province of Canada. The two formal eons of the Precambrian are subdivided into eras. In particular, the Proterozoic contains three eras: Paleoproterozoic (2.5–1.6 Ga), Mesoproterozoic (1.6–1.0 Ga) and Neoproterozoic (1.0–0.542 Ga).