Boring Billion

The Boring Billion is a term coined by palaeontologist Martin Brasier to refer to the approximately one billion-year period between 1.8 and 0.8 Ga in Earth's history that is characterized by environmental, evolutionary, and lithospheric stability. It has also been termed the "Barren Billion", "Dullest Time on Earth" and "Earth’s Middle Ages". In the time leading up to the Boring Billion, Earth experienced multiple widespread glaciations, the origin of prokaryotic life, the introduction of oxygen into the atmosphere with the evolution of cyanobacteria, addition of UV-blocking ozone to the atmosphere, and the oxidizing of iron in the oceans. After the Boring Billion, the atmosphere again underwent rapid changes as atmospheric oxygen rose to approximately modern levels, most major animal phyla evolved during the Cambrian explosion, and large animals appeared in the oceans. The Boring Billion was thus termed boring because unlike the rapidly changing environments present on Earth before and after this period, it is characterized by climatic stability, low levels of atmospheric oxygen, lack of biological events, and the absence of extreme changes in the atmospheric and oceanic composition. Stability during the Boring Billion may be attributed to a relatively stable supercontinent that was initiated by 1.7 Ga and persisted until its breakup around 0.75 Ga. The exact timing and duration of the Boring Billion is not agreed upon by scientists and estimates for the beginning and end of the Boring Billion range between 1.8 and 2.4 Ga for initiation and between 0.5 and 0.8 Ga for termination. The Boring Billion occurred during the Proterozoic Eon.

During the Boring Billion, green and purple photosynthetic bacteria appear to have thrived in an anoxic and sulfidic ocean. This ocean was much less productive than modern oceans, released sulfurous gasses including toxic hydrogen sulfide, and was very limited in nutrients (especially Mo, Fe, N, and P). As the Boring Billion progressed, eukaryotic life evolved from a prokaryotic ancestor within this ocean. By the end of the Boring Billion, the first life had appeared on land. Eukaryotes, specifically a proto-lichen, helped end the Boring Billion by causing Earth’s second oxygenation event and the Snowball Earth glaciation that accompanied it.

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