Siderian Period

What happened during this time?

 Geochemical

• Oxygen increases in the atmosphere, creating the Oxygen Catastrophe or Great Oxidation Event

  • Compared to the Archean levels, oxygen rose 10,000 times, which is still 10% of modern levels (Ossa et al., 2022). 

  • Oxygen in the atmosphere reacted with organic material in sediments, "creating a regulatory mechanism whereby the oxygen was consumed by the sediments at the same rate at which it was produced." (Daines et al., 2017)

  • The atmosphere would have changed from an orange, methane-rich hue to blue. 

  • Ultraviolet light split oxygen molecules to form single oxygen atoms, creating the first ozone layer (O3), shielding the Earth from ultraviolet radiation.

• This era had a sulfidic ocean with an oxygen-rich layer at the top of the sea and an anoxic sulfide layer deeper down (Canfield, 1998; Anbar & Knoll, 2002; Guilbaud et al., 2015).

  • The surface waters of the oceans would have been the first to become oxygenated due to agitation by wind and waves, although deeper areas of the seas would have remained anoxic. 

  • The increased atmospheric oxygen would have weathered sulfate minerals on land, sending them into the ocean during rainstorms. 

• Banded iron formations (BIFs) were abundant, which form from oxygen bonding with iron in the oceans

  • Iron was dissolved in oceans and oxidized by photosynthetic bacteria into insoluble magnetite (Fe3O4) and hematite (Fe2O3), which precipitated and formed deposits on the ocean floor

  • These deposits are layered in cycles

  • Trapped inside BIFs, there is 20x more oxygen than today's atmosphere

• Huronian glaciation begins during this period (2.4 Ga)

  • Oxygen interacted with methane, creating water and carbon dioxide. 

  • The replacement of methane would have caused global cooling, leading to ice formation as glaciers and the dropping of sea levels. 

  • Lasts until 300 million years into Rhyacian (2.1 Ga)!

Biological

• Stromatolites with cyanobacteria continue to belch oxygen into the atmosphere

  • Proposed "multicellularity" in cyanobacteria around 2.3 Ga (Schirrmeister et al., 2013)

  • Cyanobacteria may have evolved multicellular forms between 3.5–3.0 bya (Grosberg & Strathmann, 2007; Knoll, 2003; Schopf, 1993).

• Evidence of microbial mats on the land during this time (Lenton & Daines, 2016)

• Many anaerobic bacteria go extinct due to an increase in oxygen

• Around 2.4 Ga, fungal-like fossils from South Africa (Bengtson et al., 2017a)

  • These fossils were deposited in ancient deep ocean sediments

  • They appear hyphal-like and occasionally anastomose, touching and entangling each other. 

  • Compared to the size and organization of bacteria, these fossils appear eukaryotic, with morphologies representative of fungal growth.