Definition of Proterozoic in US English:



  • 1Relating to or denoting the eon that constitutes the later part of the Precambrian, between the Archean eon and the Cambrian period, in which the earliest forms of life evolved.

    The Proterozoic lasted from about 2,500 million to 570 million years ago. For millions of years only bacteria, algae, and other simple organisms existed, and the early invertebrates that followed were soft-bodied and rarely left any trace in the form of fossils

    • ‘The key to understanding the early evolution of eukaryotes lies in the Proterozoic fossil record, especially microfossils.’
    • ‘Archean and most Proterozoic sedimentary rocks are notable for their distinct lack of any bioturbated textures.’
    • ‘The bulk of the Mozambique belt of eastern Africa and Madacascar is underlain by deeply eroded and multiply deformed high-grade Proterozoic and Archaean rocks.’
    • ‘No rock standard has been identified formally as marking the base; at the top of the Proterozoic the Cambrian - Precambrian boundary is identified on the basis of fossils.’
    • ‘This is the general name for all Archaean and Proterozoic basement gneisses of the NW Scotland mainland and Outer Hebrides.’
    1. 1.1as noun the Proterozoic The Proterozoic eon or the system of rocks deposited during it.


Late 19th century: from Greek proteros ‘former’ + zōē ‘life’, zōos ‘living’ + -ic.