Precambrian

The Precambrian ( from Latin prae before = and Cambrian ) or Erdfrühzeit, obsolete designation Abiotikum, is a period in Earth's history. It covers the period from the formation of the Earth was created around 4.56 billion years ago to the development of the animal world at the beginning of the Cambrian period about 541 million years ago. The Precambrian geological eons includes the Hadean, Archean and Proterozoic.

Origin of life

On the origin of life on earth there are only a number of assumptions, such as formation processes have been observed neither in nature, nor could be shown experimentally. Anyway prevailed in the early Precambrian very different chemical and climatic conditions than later. It is believed that life could possibly have formed in the " primordial soup " of chemical reactions (see Miller - Urey experiment ). There are next to theories, representing the assumption that life is supposed to have been caused or encouraged by the impact of asteroids or comets or individual amino acids or even living cells with these extraterrestrial rocks could be reached on the Earth ( panspermia ).

In the Precambrian, the first living beings, of which only few fossils are preserved, such as bacteria such as cyanobacteria developed. The period of the Precambrian, from the known fossils, is sometimes referred to as Kryptozoikum and from Azoikum in which it probably was no life on earth, delineated.

First living things

The exact timing of the development of life is not known. However, have about 3.8 Ga ( Ga = billion years ) old rocks on islands west of Greenland on an organic origin. There are next to well-preserved fossil bacteria, namely as stromatolites socialized cyanobacteria ( formerly called blue-green algae ) with an age of 3.46 Ga, which are found in Western Australia. Another find in the same area has bacteria that are already 100 Ma older. At the end of the Precambrian, however, there are a number of well-preserved evidence of early types.

Towards the end of the Precambrian and multicellular organisms, which are expected to partly under the harbinger of still existing groups of organisms originated as sponges ( Porifera ) and cnidarians ( Cnidaria ), but partly also difficult or impossible to classify in the plans currently known groups of organisms. Locations of Precambrian formations are rare on Earth, and the ancient rocks were often reshaped several times by tectonic processes. The name derives from the Ediacaran fauna, a community of life of the late Precambrian, the Ediacara Formation of Flinders Range in Australia, their equivalents are also found in Canada and Namibia. This final section of the Precambrian is called the Ediacaran or Vendian formerly known as ( cf. Vendobionten ).

Geology

The mass of the rock is plutonic and volcanic origin, very much changed by the user of the metamorphism. In most Precambrian granites occur. The rocks are locally very rich in valuable usable deposits (gold, copper, nickel, iron, etc.).

Subdivision of the Precambrian

The Precambrian consists of the following units:

  • Aeon: Proterozoic ( 2500-541 mya ) Era: Neoproterozoic ( 1000-541 mya )
  • Era: Mesoproterozoikum ( 1600-1000 mya )
  • Era: Paleoproterozoic ( 2500-1600 mya )
  • Era: Neoarchaikum ( 2800-2500 mya )
  • Era: Mesoarchaikum ( 3200-2800 mya )
  • Era: Paläoarchaikum ( 3600-3200 mya )
  • Era: Eoarchaikum ( 4000-3600 mya )

Continents and climate

The locations of the fossils of the Ediacaran fauna are on different continents today. Through this stratigraphic evidence is proof that at that time the land masses were merged into one " super continent ", to whom they gave the name of Rodinia. Traces of Precambrian glaciation in Namibia and Canada speak for one or more global ice ages in the Precambrian ( Snowball Earth ). Only the transition to a warmer climate made ​​the Cambrian explosion, better described as the Cambrian Radiation, of life on earth at the start of the Cambrian possible.

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