Orosirian Period

Extensive mountain building

The Orosirian is the third period of the Paleoproterozoic Era, occurring after Rhyacian, and before the Statherian. "Orosirian" is named for the extensive mountain building (orogeny), which occurred during this time.

Geologic Age

2,050–1,800 Ma

Eon / Era

Proterozoic; Paleoproterozoic

What happened during this time?

Geological

The early continents (Ur, Nena, and Atlantica) moved towards each other
- A supercontinent, called Columbia or Nuna, starts to form (between 2.1 Ga and 1.8 Ga)
The activity of sulfur bacteria controlled or influenced the formation of the Earth’s earliest phosphorites.
Two of the largest bolide impact events in Earth's history occurred during this time

Vredefort Crater

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.

Sudbury Crater

Crater known as Sudbury Basin (Ontario, Canada)
A 250 km wide crater formed at the end of the Orosirian (1.85 billion years ago).
The impactor was an asteroid at least 10 km in size

Above: Continent placement during the Orosirian Period

Below: Figure 1 from Allen et al., 2022 showing the Vredefort crater

Biological

Prokaryotic cyanobacteria continue to dominate

Gunflint Biota

The Gunflint Chert from Minnesota and Ontario (Tyler & Barghoorn, 1954; Barghoorn & Schopf, 1965) records evidence of increasing complexity in Precambrian life from ~1.88 Ga
This is a banded iron ore formation with delicate preservation
Evidence of cyanobacterial stromatolites
Gunflint microorganisms are divided into several types: spheres, branched and unbranched filaments, unbranched tubes, and bizarre forms. Unicellular and multicellular forms are found within the chert.
- Filaments show the ability to divide cells in 1 plane of division, forming a string of connected cells (filamentous)
- Branched filaments can divide in 2 planes of division, forming "branches" of filamentous strands; this is evidence of increased complexity in the fossil record.
Most Gunflint microfossils are small (<10 μm in diameter), but some were larger (e.g., 10–100 μm in diameter), which puts them in a different size range than prokaryotes (Knoll et al., 2006).
- Some of the earliest evidence of acritarchs (microfossils from unicellular photosynthetic protists) was found in the black chert layers
- These acritarchs were probably some of the earliest eukaryotes
- The Last Eukaryotic Common Ancestor (LECA) existed during this time. This organism would be the ancestral parent to all living eukaryotes, giving rise to all known algae, plants, fungi, and animals.

Grypania spiralis

- Morphotaxon for a coiled, filamentous algae 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 & Williams, 1990; Han & 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 mega-bacterium found in the Caribbean mangroves that can reach up to 2 cm (Volland et al., 2022)
- Some researchers think younger specimens dating to Mesoproterozoic (~1,450 mya) differ from the Paleoproterozoic 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)

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