Boring Billion

The boring billion, also referred to as the Barren Billion, is the most boring period in Earth’s history and medieval times, spanning the mid-Proterozoic period of 1.8-800 million years . Less stable crustal movements, less stagnation in climate, and less stagnation in biological evolution. Although it is limited by two different oxygen enrichments and glacial events, this period had very low oxygen levels and there is no evidence of glacial action.

Highlights

During this period, the ocean was nutrient deficient, oxygen deficient, sulfidic, and was populated by a type of photosynthetic bacterium that mainly uses low oxygen cyanobacteria and produced hydrogen sulphide and sulphur instead of water. This is known as Canfield Ocean. Such a configuration can result in a black, milky white turquoise sea instead of blue. Despite these adverse conditions, eukaryotes have evolved during the beginning of a boring billion, adopting several new adaptations such as sexual reproduction, various organelles, animals, plants and fungi. Such progress may have been an important precursor to the development of complex and large life in the later Cambrian explosion. However, prokaryotic cyanobacteria were the main organisms during this period and may have supported a low-energy food network with a small number of protists at the apex level. The planet Earth may have been inhabited by prokaryotic cyanobacteria and eukaryotic prokaryotic lichens, the latter of which may be more successful than offshore seawater due to their high availability of nutrients.

Climatic Stability during this period

There is less evidence of climate change during this period. The climate was probably not determined primarily by the brightness of the Sun, as the Sun was 5-18% less bright than it is today, but there is no proper evidence which shows that the Earth’s climate was significantly cooler. In fact, this period did not appear to have evidence of long-term glacial activity as regularly seen elsewhere in the Earth’s geological history. High levels of CO2 may not have been the main reason for warming. This is because the level needs to be 30-100 times the pre-industrial level, causing significant ocean acidification to prevent ice formation.

Oceanic Composition during this period

The ocean was an important nutrient that was believed to be necessary for complex life, namely molybdenum as well as nitrogen, iron mainly due to the lack of oxygen and the resulting oxidation required for these geochemical cycles. The concentration of phosphorus seems to be low. However, nutrients were more abundant in terrestrial environments such as coastal environments near lakes and continental outflows. In general, the ocean may have had an oxygen-rich surface, a sulphide middle layer, and a sub oxygen bottom layer. The sea may have been colored black and milky white turquoise instead of blue, mainly due to the composition of the sulphides.

Lifeform during this period

Low nutrient levels can lead to increased photosynthesis and the development of eukaryotes, where one organism photosynthesizes between prokaryotes and the other metabolizes waste products. Archaea, bacteria and eukaryotes are the three domains with the highest taxonomic ranks. Eukaryotes differ from prokaryotes in that they have organelles that are attached to the nucleus and membrane, and almost all multicellular organisms are eukaryotes. Some of the earliest evidence of prokaryotic land settlement dates back to pre-3 Gya, perhaps 3.5 Gya. During the boring billion, the land may have been predominantly inhabited by cyanobacterial mats. Dust provided abundant nutrients and dispersal means for surface microorganisms, but microbial communities may have also formed in caves, freshwater lakes and rivers. By 1.2 Gya, the microbial communities could have been rich enough to affect weathering, deposition, erosion and various other biogeochemical cycles, and extensive microbial mats were rich in biological soil crust. Early terrestrial eukaryotes may have been lichen fungi of approximately 1.3 Ga that grazed the microbial mat.