Proterozoic

[ prot-er-uh-zoh-ik, proh-ter- ]

noun

1. the longest geologic eon and the most recent division of Precambrian time, during which the presence of oxygen in Earth’s atmosphere became significant, causing certain life forms to adapt to the use of oxygen and leading to a proliferation of complex multicellular life.

adjective

1. of or relating to this eon.

Proterozoic

/ ˌprəʊtərəʊˈzəʊɪk /

noun

1. the later of two divisions of the Precambrian era, during which the earliest plants and animals are assumed to have lived Compare Archaeozoic

adjective

1. of or formed in the late Precambrian era

Proterozoic

/ prŏt′ər-ə-zō′ĭk /

1. The later of the two divisions of the Precambrian Eon, from about 2.5 billion to 540 million years ago. The Proterozoic was characterized by the formation of stable continents, the appearance of abundant bacteria and archaea, and the buildup of oxygen in the atmosphere. By about 1.8 billion years ago the oxygen buildup was significant enough to cause many types of bacteria to die out. At this time eukaryotes, including multicellular algae and the first animals, first appear in the fossil record.
2. See Chart at geologic time

Word History and Origins

Origin of Proterozoic¹

First recorded in 1905–10; protero- + zo- + -ic

Example Sentences

This could have helped the planet's warming during the Proterozoic era - a stage when oxygen had just appeared in the atmosphere and complex life had not yet formed.

From BBC

The microscopic fossils, contained in shale rock from the Northwest Territories of Canada, dated to the Proterozoic era before the advent of complex life forms.

From Reuters

The Proterozoic—the geologic eon that preceded the Cambrian period and spanned the time from the appearance of oxygen in Earth’s atmosphere to the emergence of complex life—is itself nearly two billion years long.

From Scientific American

Back in the Proterozoic, a few million years after multicellular life appeared on the planet, the moon was about 211,825 miles away from Earth—about 21,000 miles closer than it is today.

From National Geographic

Others divide the Precambrian into two eras, the very ancient Archean and the more recent Proterozoic.

From Literature