Proterozoic

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Aeonothem Arathem system Age
( mya )
later later later
P
r
o
t
e
r
o
z
o
i
k
u
m

Duration:

1959
Ma 		Neoproterozoic
Jungproterozoikum
Duration: 459 Ma 		Ediacarium 541
⬍
635
Cryogenium 635
⬍
720
Tonium 720
⬍
1000
Mesoproterozoic
Mittelproterozoikum
Duration: 600 Ma 		Stenium 1000
⬍
1200
Ectasium 1200
⬍
1400
Calymmium 1400
⬍
1600
Paleoproterozoic
Altproterozoikum
Duration: 900 Ma 		Statherium 1600
⬍
1800
Orosirium 1800
⬍
2050
Rhyacium 2050
⬍
2300
Siderium 2300
⬍
2500
earlier earlier earlier

The Proterozoic (composed of the Greek words πρότερος próteros , German 'previous' , 'early' and ζῶον zôon , German 'living being' ), formerly also called Algonkian or Eozoic , is an aeon of geological development in the Precambrian . It ranges from the end of the Archean , around 2500 million years ago to around 541 million years ago.

History and naming

The term Proterozoic was first proposed in its English form as Proterozoic by Samuel Franklin Emmons at the 5th International Geological Congress. He referred to the temporal position of clastic formations between the Archean and the Cambrian. The name was intended to indicate that the living environment documented in these formations appears earlier than that of the Paleozoic Era without having to commit to the fact that these were the first traces of life at all.

the atmosphere

The Proterozoic is characterized by the presence of an oxygen-containing atmosphere . Already towards the end of the Archean , before 2500 mya, the oxygen content in the earth's atmosphere began to rise. Although the production of oxygen by photosynthesizing organisms had already started around a billion years earlier, it was only from this point in time that oxygen was released into the atmosphere. Previously, this process was the oxygen uptake during the oxidation of the dissolved inorganic substances in sea water, in particular iron - ions and ions of other heavy metals is prevented. These metal ions, present in the reduced state, were oxidized to metal oxides in the course of time, only then could free oxygen enter the atmosphere. With increasing oxygen concentration in the atmosphere, ozone could also be formed, which was able to filter UV light that is harmful to living beings . Only oxygen made the development of animal life possible.

The climate was also at times significantly different from today; there are indications of global icing ( Snowball Earth , Snowball Earth ).

Development of life

The name Proterozoic indicates that it is the time of the beginning of animal life. Fossil remains of living things, which are difficult to assign to the animal phyla known today, have been found. Since these first animal forms had hardly any skeletons or hard shells, many morphological structures have not been preserved and their forms are difficult to reconstruct. In addition, the fossil-bearing strata were exposed to geological changes over time. Strange communities, such as those preserved in the fossils of the well-known Ediacaran fauna , formed in the shallow, warm seas near the coast. With the end of the Proterozoic at the turn of the Cambrian , most of the tribes of the animal kingdom seem to have already been present as the exit for the Cambrian explosion that followed.

Subdivision of the Proterozoic

The green alga Grypania spiralis from the Paleo- and Mesoproterozoic is one of the oldest multicellular eukaryotes (length between 1 and 3 cm). Its oldest, 2.1 billion year old fossils from the Negaunee Iron Formation in Michigan (USA) are among the first known body fossils

It is divided into the following aera topics :

An alternative structure looks like this:

See also

Web links

Commons : Proterozoikum  - collection of images, videos and audio files

Individual evidence

  1. ↑ SF Emmons: Letter to Persifor Frazer, dated May 25, 1887 . In: International Geology Congress, American Committee Reports . Philadelphia 1988, p. A58 (English).