AskDefine | Define Proterozoic

Dictionary Definition

proterozoic adj : formed in the later of two divisions of the Precambrian era; "proterozoic life forms" n : from 2,500 to 544 million years ago; bacteria and fungi; primitive multicellular organisms [syn: Proterozoic eon, Proterozoic aeon]

User Contributed Dictionary

English

Pronunciation

Adjective

  1. Of, or relating to the geologic eon from about 2,500 to 570 million years ago; comprises the Paleoproterozoic, Mesoproterozoic and Neoproterozoic eras; marked by the build up of oxygen in the atmosphere and the emergence of primitive multicellular life.

Proper noun

  1. The Proterozoic eon.

Translations

Proterozoic eon
  • Croatian: proterozoik, algonkij

Extensive Definition

The Proterozoic () is a geological eon representing a period before the first abundant complex life on Earth. The Proterozoic Eon extended from 2500 Ma to 542.0 ± 1.0 Ma (million years ago), and is the most recent part of the old, informally named ‘Precambrian’ time.
The Proterozoic consists of 3 geologic eras, from oldest to youngest:
The well-identified events were:

The Proterozoic record

The geologic record of the Proterozoic is much better than that for the preceding Archean. In contrast to the deep-water deposits of the Archean, the Proterozoic features many strata that were laid down in extensive shallow epicontinental seas; furthermore, many of these rocks are less metamorphosed than Archean-age ones, and plenty are unaltered. Study of these rocks show that the eon featured massive, rapid continental accretion (unique to the Proterozoic), supercontinent cycles, and wholly-modern orogenic activity.
The first known glaciations occurred during the Proterozoic, one began shortly after the beginning of the eon, while there were at least four during the Neoproterozoic, climaxing with the Snowball Earth of the Varangian glaciation.

The build-up of oxygen

One of the most important events of the Proterozoic was the gathering up of oxygen in the Earth's atmosphere. Though oxygen was undoubtedly released by photosynthesis well back in Archean times, it could not build up to any significant degree until chemical sinks — unoxidized sulfur and iron — had been filled; until roughly 2.3 billion years ago, oxygen was probably only 1% to 2% of its current level. Banded iron formations, which provide most of the world's iron ore, were also a prominent chemical sink; most accumulation ceased after 1.9 billion years ago, either due to an increase in oxygen or a more thorough mixing of the oceanic water column.
Red beds, which are colored by hematite, indicate an increase in atmospheric oxygen after 2 billion years ago; they are not found in older rocks.

Paleogeography

The Mackenzie dike swarm in Canada's Canadian Shield is the largest known dike swarm on Earth, and was a source for significant massive flood basalt eruptions throughout the Proterozoic period. The source for the Mackenzie dike swarm is thought to have been a mantle plume center called the Mackenzie hotspot.

Proterozoic life

The first advanced single-celled and multi-cellular life roughly coincides with the start of the accumulation of free oxygen; this may have been due to an increase in the oxidized nitrates that eukaryotes use, as opposed to cyanobacteria.
The blossoming of eukaryotes such as acritarchs did not preclude the expansion of cyanobacteria; in fact, stromatolites reached their greatest abundance and diversity during the Proterozoic, peaking roughly 1.2 billion years ago.
Classically, the boundary between the Proterozoic and the Phanerozoic eons was set at the base of the Cambrian period when the first fossils of animals known as trilobites and archeocyathids appeared. In the second half of the 20th century, a number of fossil forms have been found in Proterozoic rocks, but the upper boundary of the Proterozoic has remained fixed at the base of the Cambrian, which is currently placed at 542 Ma.

References

External links

Proterozoic in Breton: Proterozoeg
Proterozoic in Catalan: Proterozoic
Proterozoic in Czech: Proterozoikum
Proterozoic in Danish: Proterozoikum
Proterozoic in German: Proterozoikum
Proterozoic in Estonian: Proterosoikum
Proterozoic in Modern Greek (1453-): Προτεροζωικός αιώνας
Proterozoic in Spanish: Eón Proterozoico
Proterozoic in Esperanto: Proterozoiko
Proterozoic in French: Protérozoïque
Proterozoic in Galician: Proterozoico
Proterozoic in Korean: 원생누대
Proterozoic in Indonesian: Proterozoikum
Proterozoic in Italian: Proterozoico
Proterozoic in Hebrew: פרוטרוזואיקון
Proterozoic in Kazakh: Протерозой
Proterozoic in Latin: Aeon Proterozoicus
Proterozoic in Lithuanian: Proterozojus
Proterozoic in Hungarian: Proterozoikum
Proterozoic in Dutch: Proterozoïcum
Proterozoic in Japanese: 原生代
Proterozoic in Norwegian: Proterozoikum
Proterozoic in Low German: Proterozoikum
Proterozoic in Polish: Proterozoik
Proterozoic in Portuguese: Proterozóico
Proterozoic in Russian: Протерозой
Proterozoic in Slovak: Proterozoikum
Proterozoic in Slovenian: Proterozoik
Proterozoic in Serbo-Croatian: Proterozoik
Proterozoic in Finnish: Proterotsooinen eoni
Proterozoic in Swedish: Proterozoikum
Proterozoic in Vietnamese: Liên đại Nguyên Sinh
Proterozoic in Turkish: Proterozoik Devir
Proterozoic in Ukrainian: Альгонкська ера
Proterozoic in Chinese: 元古宙
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