Stenian Period
Super-continent Rodinia forms
The Stenian is the third and final period of the Mesoproterozoic, occuring after Ectasian, and before the (Tonian) Neoproterozoic
Geologic Age
1,200–1,000 Ma (1.2–1.0 Ga)
Subdivisions
No subdivisions
"Stenian" is Greek for "narrow", referring to the narrow belts that formed during this period
Eon / Era
What happens during this time?
Biological
Origin of eukaryotes
Bangiomorpha pubescens
a multicellular filament (~1,200 Ma) from the Hunting Formation, Canada (Butterfield et al., 1990; Butterfield, 2000) is the earliest evidence of eukaryotes
Bangiomorpha exhibits a number of characters found within both the red algae and green algae, as well as cyanobacteria
It also exhibits an unusual pattern of cell division not known outside the red algal family Bangiaceae (Butterfield et al., 1990; Butterfield, 2000).
Additional evidence for multicellular photosynthetic eukaryotes comes from younger filamentous microfossils
Evidence of sexual reproduction
Prokaryotes do not perform sexual reproduction; this is a strictly eukaryotic function
Finding evidence of sexual reproduction in the fossil record is difficult, but the products of meiosis could serve as proof
Four haploid cells (spores or gametes) connected in a tetrad pattern can indicate meiosis
Sexual reproduction and true (eukaryotic) multicellularity probably occur around the same time. Therefore, multicellular organisms probably reproduce by sex. reproduction
There is no clear evidence of life colonizing land
Even with the lack of evidence, there was probably prokaryotic organisms on the land
Microbes may have been present on land (Catling & Buick, 2012) much earlier (e.g., 2.75 Ga)
This evidence comes from the record of how sulfur and molybdenum levels increased in the oceans around this time
The simultaneous increase of both indicates that microbes on land may have been breaking down rock, which washed into the sea
The evidence is not clear, and it may be some time before we understand the extent of early colonization of land by microbes
Proterocladus antiquus
Seaweed-like green alga from China found at roughly 1.0 Ga (Tang et al. 2020)
This is the earliest evidence of multicellularity in green algae to date
Other organisms
Maximum diversity of stromatolites
Profuse growths of stromatolites along the coastlines
Stromatolites begin to precipitously decline at about 1.0 Ga (Bernard et al. 2013)
Eukaryote fossils called Paleovaucheria clavata (German, 1981)
Toward end of Stenian, ancestral unikonts (e.g. group with fungi, animals, etc.) lose flagella giving rise to slime molds
Geological
The atmosphere, which had contained about 1% of oxygen at the start of the Mesoproterozoic, had increased the oxygen content to no more than 2-4% at the time of the formation of Rodinia.
There was no ozone layer.
Rodinia
The formation of the supercontinent Rodinia during the Grenville Orogeny.
Continents started drifting towards each other after splitting apart during Ectasian
Rodinia produced some significant changes in the Earth.
It was the largest landmass to have existed up till that time.
It significantly changed ocean currents, which may have led to snowball Earth later in the Cryogenian.
The center of the continent was a vast floodplain, accumulating silts and sedimentary deposits over the years.
Massive flooding due to lack of terrestrial plant life
A giant basin of sedimentary rocks known as the "Belt Supergroup" extends across Alberta, British Columbia, Montana, Idaho, and Washington. These are mostly sandstone, siltstone, and limestone. They show beautifully preserved features like cracks, ripples, and stromatolites.
Rodinia was surrounded by a single ocean, known as Mirovia.
The eight continents that made up Rodinia later reassembled briefly into another continent, Pannotia, and again into Pangaea.
Above: Bangiomorpha, one of the earliest known eukaryotes, possibly red algae
Above: Proterocladus from Mesoproterozoic
