Orosirian Period
Extensive mountain building
The Orosirian is the third period of the Paleoproterozoic Era, occurring after Rhyacian, and before the Statherian.
Geologic Age
2,050–1,800 Ma
"Orosirian" is named for the extensive mountain building (orogeny), which occurred during this time.
Eon / Era
What happened during this time?
Geological
Movement of the early continents (Ur, Nena and Atlantica) moved towards each other
A supercontinent, called Columbia or Nuna, starts to forms (between 2.1 Ga - 1.8 Ga)
The activity of sulfur bacteria controlled, or influenced the formation of the Earth’s earliest phosphorites.
Two of the largest impact events occured during this time
Crater near Vredefort (Free Province of South Africa) around 160 miles in diameter at impact (Allen et al. 2022)
An asteroid over 10-15 miles in diameter traveling at a velocity of nearly 34,000 miles per second crashed near present-day Johannesburg, South Africa
Formed at the beginning of the Orosirian (2.023 billion years ago)
Much bigger than the impact that killed the non-avian dinosaurs
Dust and aerosols from the Vredefort impact would have spread across the planet and blocked sunlight, cooling the Earth's surface effecting photosynthesis
Greenhouse gases such as carbon dioxide that were emitted from the impact would have raised the global temperature potentially by several degrees for a long period of time.
Crater known as Sudbury Basin (Ontario, Canada)
250 km wide crater formed the end of the Orosirian (1.85 billion years ago).
The impactor was an asteroid at least 10 km in size
Biological
Prokaryotic cyanobacteria organisms continue to dominate
The Gunflint Chert from Minnesota and Ontario (Barghoorn & Tyler 1965) records evidence of increasing complexity in Precambrian life from ~1.88 bya
Evidence of stromatolites
Some of the earliest evidence of acritarchs found in the black chert layers
Above: Continent placement during the Orosirian Period
Below: Figure 1 from Allen et al. 2022 showing the Vredefort crater
Appearance of Grypania spiralis which has a coiled, filamentous appearance that does not branch
Grypania has been observed at lengths over ½ meter (1½ feet) in length, but only 2 mm in diameter.
Specimens are found stretching from the Paleoproterozoic to the Neoproterozoic
The original dating is around 2.1 Ga (Grey and Williams 1990; Han and Runnegar 1992; Kumar 1995), although these older specimens are not well preserved and debated
Paleoproterozoic specimens of Grypania could also be giant bacterium or bacterial super colony, similar to Thiomargarita magnifica, a megabacterium found in the Caribbean mangroves that can reach up to 2 cm (Volland et al. 2022)
Some researchers think that younger specimens dating to Mesoproterozoic (~1,450 mya) are different from the Paleproterozoic specimens (Knoll et al. 2006).
These younger specimens are almost definitely eukaryotes possibly green, Chlorophyceae algae
Above: An early eukaryotic algae, Grypania
Additional Web Pages
The asteroid that formed Vredefort crater was bigger than previously believed (Phys.org 26Sep2022)