It is most widely accepted that stromatolites from the late Archean and through the middle Proterozoic eon were mostly formed by massive colonies of cyanobacteria ( formerly known as blue-green algae ), and that the oxygen byproduct of their photosynthetic metabolism first resulted in earth ’ s massive banded iron formations and subsequently oxygenated earth ’ s atmosphere.

The Hadean eon represents the time before fossil record of life on Earth ; its upper boundary is now regarded as 4. 0 Ga. Other subdivisions reflect the evolution of life ; the Archean and Proterozoic are both eons, the Palaeozoic, Mesozoic and Cenozoic are eras of the Phanerozoic eon.

The Paleozoic comes after the Neoproterozoic era of the Proterozoic eon, and is followed by the Mesozoic era.

The Proterozoic eon is divided into three eras: the Neoproterozoic, Mesoproterozoic and Paleoproterozoic.

The Proterozoic () is a geological eon representing the time just before the proliferation of complex life on Earth.

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 Sturtian and Marinoan glaciations.

It is at least certain that by the end of the Proterozoic eon, most of the continental mass lay united in a position around the south pole.

The Archean (, also spelled Archaean ; formerly Archaeozoic ), also spelled Archeozoic or Archæozoic ) is a geologic eon before the Proterozoic Eon, before 2. 5 Ga ( billion years, or 2, 500 ) ago.

Its Earth equivalents are the Neoproterozoic era of the Proterozoic eon and the whole of the Phanerozoic eon.

Its Earth equivalent consists of most of the Neoarchean era ( Archean eon ), Paleoproterozoic and Mesoproterozoic eras ( Proterozoic eon ).

Radiometric dating gives an age of 1700 million years for the metamorphism, placing it in the early part of the Proterozoic eon.

Earth ’ s deep time in the Proterozoic and deeper still in the Archean is only " recounted by microscopic fossils and subtle chemical signals.

Older time spans which predate the reliable fossil record ( before the Proterozoic Eon ) are defined by absolute age.

The time before the Phanerozoic, called the Precambrian supereon, is now divided into the Hadean, Archaean and Proterozoic eons.

The Proterozoic Eon extended from to ( million years ago ), and is the most recent part of the informally named ‘ Precambrian ’ time.

Another round of uplift exposed the Beck Spring rocks and the underlying Crystal Spring to erosion ; subsequent faster subsidence of the Amargosa aulacogen broke these formations into islands in later Proterozoic time.

Lower Proterozoic Stromatolite s from Bolivia, South America

However, macroscopic fossils are now known from the late Proterozoic.

** Neoproterozoic: The youngest geologic era of the Proterozoic Eon, from the Cambrian Period lower boundary ( 542 Ma ) back to 1000 Ma.

Lower Proterozoic Stromatolites from Bolivia, South America

The name Proterozoic comes from Greek and means " earlier life ".

When the Archean began, the Earth's heat flow was nearly three times higher than it is today, and it was still twice the current level at the transition from the Archean to the Proterozoic ( 2, 500 ).

It was naturally formed from the quartz of the Kadapa Supergroup of the Middle to Upper Proterozoic ( 1600 to 570 Ma ) due to erosive forces.

This compositional range is intermediate, and is one of the characteristics which distinguish Proterozoic anorthosites from Archean anorthosites.

They are distinct texturally and mineralogically from Proterozoic anorthosite bodies.

The sedimentary rock exposed in this dome range in age from Late Proterozoic within the center of the dome to Ordovician sandstone around its edges.

Proterozoic carbonaceous remains from the Chorhat sandstone: oldest fossils of the Vindhyan supergroup.

" Greenstone belts " are distributed throughout geological history from the Phanerozoic Franciscan belts of California where blueschist, whiteschist and greenschist facies are recognised, through to the Palaeozoic greenstone belts of the Lachlan Fold Belt, Eastern Australia, and a multitude of Proterozoic and Archaean examples.

Atlantica (; Atlantika ) is the name given to an ancient continent that formed during the Proterozoic about ( two billion years ago, Ga ) from various 2 Ga cratons located in what is now West Africa and eastern South America.

Shale-Facies Microfossils from the Proterozoic Bylot Supergroup, Baffin Island, Canada.

Proterozoic gold deposits are also known from turbidite basin deposits.

The Closepet granites are a major geological feature of this region and are from the Lower Proterozoic era.

Phosphorites are known from Proterozoic banded iron formations in Australia, but are more common from Paleozoic and Cenozoic sediments.

They also vary widely in age, from Proterozoic to Pleistocene, the youngest known example being 56, 000 ± 5, 000 years old.

This fault zone ( composed of several different individual faults ) lies at the base of the main scarp of the Adelaide Hills, separating the young Quaternary alluvium of the plains from the Proterozoic sedimentary rocks making up the ranges.

This suggests that Precambrian organisms were employing the same elements, albeit for a different purpose — perhaps to avoid the inadvertent precipitation of calcium carbonate from the supersaturated Proterozoic oceans.

The alkaline granite here was formed in the Proterozoic 1500 million years ago from a dome of molten magma.

Overall, this part of New York is represented by lower Paleozoic sedimentary rocks that unconformably overlie the Grenville-aged ( Proterozoic, here about 1. 1 billion years old ) metamorphic rocks of the Adirondacks.

The Ediacaran Period, named after the Ediacara Hills of South Australia, is the last geological period of the Neoproterozoic Era and of the Proterozoic Eon, immediately preceding the Cambrian Period, the first period of the Paleozoic Era and of the Phanerozoic Eon.

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 including 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.

They are considered to be among the most important and best-known Late Proterozoic to Cambrian sections in the United States.

Depending on the differing points of view, the crater may be of earlier Cambrian or Proterozoic age, or it could be of younger Paleozoic age.