Stenian

Before the Stenian was defined as a period in 1991, the Riphean age was defined from 1600 to 600 Mya, primarily used in Russia and textbooks across the world.^[6] The Stenian period was created in 1991 by K.A. Plumb as part of the New Precambrian time scale, defined as 1000 to 800 Mya.^[7] The name Stenian comes from Ancient Greek: στενός, romanized: stenós, meaning narrow and referring to the narrow polymetamorphic belts in this period.^[8]

This period includes the formation of the Keweenawan Rift at about 1100 Mya which led to the Keweenawan Supergroup.^[9] The Musgrave orogeny also happened around this period from 1.22 to 1.12 billion years ago forming the Musgrave Block, with the Warakurna Large igneous province forming at 1076 ± 6 million years ago.^[10]

The Grenville orogeny mainly took place in this period spanning from 1250 to 980 Mya, with the Elzerian orogeny ending in this period, the Shawingian and Ottawan orogenies taking place entirely in the Stenian, and the Rigolet orogeny starting at 1010 Mya.^[8]

Outside of North America and Australia, the Kibaran orogeny, the Dalslandian orogeny, and the Sunsás orogeny also took effect around this time. All of these orogenies helped form and stabilize the supercontinent Rodinia.^[11][12][13]

The Torridonian supergroup was primarily formed along Scotland in this period onwards, being constrained to at most 1100 Mya.^[14][15] The Nonesuch Shale was also formed around 1.1 Gya and spans from Michigan to Iowa.^[16]

From 1.7 Gya to 1.1 Gya, there is a lack of paleosols. This also happens from the end of the period onward to 0.7 Gya.^[17] The seafloor was primarily non-oxic, with 25% oxic and recurring Euxinic episodes. ^[18]

Fossils of the oldest known sexually reproducing organism, Bangiomorpha pubescens, first appeared in the Stenian at the Hunting Formation in Somerset Island around 1.047 Bya.^{[19][1][10] [20]}The first known preserved case of multicellularity in green algae also originates from this period, specifically Proterocladus antiquus known from roughly 1 billion years ago.^[21]

Acritarchs became more abundant and spiny around this time, suggesting an increased rate in eukaryvory which forced an evolutionary response.^[10]

Stromatolites peaked in diversity in this period and swiftly declined in numbers at the end of the period around 1 billion years ago.^[22][23] Eukaryotes seem to have dominated non-marine habitats by 1 Ga.^[24]

The oxygen level during the Stenian was still low compared to today, being around 0.5% to 5% present atmospheric levels.^[18][25] There were no major glaciation events and the length of day was approximately 18.94 ± 0.39 h.^[26]

• Boring Billion – Earth history, 1.8 to 0.8 billion years ago
• Riphean (stage) – Stage in the geological timescale named after the UralsPages displaying short descriptions of redirect targets
• Grenville orogeny – Mesoproterozoic mountain-building event