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

No subdivisions
"Stenian" is Greek for "narrow", referring to the narrow belts that formed during this period

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

Origin of sexual reproduction

Finding evidence of sexual reproduction in the fossil record is difficult
Prokaryotes do not perform sex. reproduction; this is a strictly eukaryotic function
Evidence of meiosis is the hallmark of sexual reproduction
- A diploid cell that produces 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 reproduced by sex. reproduction

No clear evidence of life colonizing land
- Possible prokaryotic organisms on land
- Microbes may have present on land (Catling and Buick 2012) that indicates that microbes may have colonized land much, much ealier, as early as 2.75 billion years ago. 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.
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

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.
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
  - Giant basin of sedimentary rocks known as the "Belt Supergroup" extends across Alberta, British Columbia, Montana, Idaho and Washington. These are mostly sandstone, silt-stone, 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 which made up Rodinia later reassembled briefly into another super continent Pannotia, and again into Pangaea.

Above: Bangiomorpha, one of the earliest known eukaryotes, possibly red algae

Above: Proterocladus from Mesoproterozoic