Proterozoic Eon

Proterozoic Eon

Equatorial Ice

Earth's Snowball State in the Proterozoic Eon

Cyanobacteria and Oxygenation

Also known as blue-green algae

Climate and Atmosphere

Organisms

Atmospheric CO2 history

Atmospheric CO2 level

Proterozoic Eon

Eukaryotic cells

2 billion years

Multicellular life

Large oxygen excess

Major Event

Source of the Great Oxygenation Event

Interesting Facts

Rodinia supercontinent

Complex animals and plants

Stromatolites

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Major Event

One major event during the Proterozoic Eon was the Great Oxygenation Event (GOE), which occurred around 2.4 billion years ago. This event marked the significant increase in atmospheric oxygen levels due to the photosynthetic activity of cyanobacteria. It led to the oxidation of Earth's surface and oceans, fundamentally altering the planet's geochemistry and enabling the evolution of aerobic life forms.

Cyanobacteria

During the Proterozoic Eon, life on Earth evolved from simple, single-celled organisms to more complex multicellular forms. Cyanobacteria played a crucial role in oxygenating the atmosphere through photosynthesis, paving the way for the emergence of aerobic organisms.

Climate and Atmosphere

The Proterozoic Eon was characterized by significant changes in Earth's climate and atmosphere. Early in the eon, the planet was largely covered by ice during a series of glaciations known as "Snowball Earth" events. Later, the climate became warmer, leading to the melting of glaciers and the development of oxygen-rich atmospheres.

Duration:

The Proterozoic Eon lasted approximately 2 billion years, from about 2.5 billion to 541 million years ago.

Geological and palaeomagnetic studies

“Geological and palaeomagnetic studies indicate that ice sheets may have reached the Equator at the end of the Proterozoic eon, leading to the suggestion of a fully ice-covered snowball Earth"4. Climate model simulations indicate that such a snowball state for the Earth depends on anomalously low atmospheric carbon dioxide concentrations'6, in addition to the Sun being 6 per cent fainter than it is today. However, the mechanisms producing such low carbon dioxide concentrations remain controversial.”

Donnadieu, Y., Goddéris, Y., Ramstein, G., Nédélec, A., & Meert, J. (2004). A “snowball Earth” climate triggered by continental break-up through changes in runoff. Nature, 428(6980), 303–306. https://doi.org/10.1038/nature02408

Atmospheric CO2 history

Steady-state atmospheric CO2 level achieved by the GEOCLIM model for the SC runs, for the SC runs with the inclusion of basaltic provinces (denoted SC trap), and for the DC runs also with basaltic provinces (denoted DC trap).

Vertical bars denote the upper and the lower range of atmospheric CO levels calculated using (for the SC runs) a 20% increase and a 20% decrease in degassing flux, and (for the SC trap and DC trap runs) a 20% increase and a basaltic surface of 4 x 10 km? and a 20% decrease and a basaltic surface of 8 x 10* km? (see Methods). Dark grey area as Fig. 2. The vertical arrow displays the change of the radiative forcing from direct CO2 effects alone.

Donnadieu, Y., Goddéris, Y., Ramstein, G., Nédélec, A., & Meert, J. (2004). A “snowball Earth” climate triggered by continental break-up through changes in runoff. Nature, 428(6980), 303–306. https://doi.org/10.1038/nature02408

Cyanobacteria and Oxygenation:

Cyanobacteria, also known as blue-green algae, were pivotal during this time. Through photosynthesis, they released oxygen as a byproduct, leading to a significant increase in atmospheric oxygen levels. This process, known as the Great Oxygenation Event, fundamentally altered the chemistry of the Earth's atmosphere and oceans, creating conditions conducive to the development of aerobic organisms.

Large oxygen excess

Large oxygen excess in the primitive mantle could be the source of the Great Oxygenation Event. Micrograph of an Al-bearing (Mg,Fe)SiO3 bridgmanite. The starting material consisting of a mixture of (Mg,Fe)SiO3 pyroxene and Al2O3 corundum was compressed to 40 GPa and heated to 2500 K, using the LH-DAC. The reaction between the two phases induced the Fe2+ disproportionation into a mixture of Fe3+-rich, Al-bearing bridgmanite (large grey areas) and metallic Fe0 (dark droplets). Early in the Earth’s history, core segregation drained the metallic Fe0 away from the Fe3+-rich Bg, thus leaving the deep mantle with a large oxygen excess.

Andrault, D., Muñoz, M., Pesce, G., Cerantola, V., Chumakov, A., Kantor, I., Pascarelli, S., Rüffer, R., & Hennet, L. (2018). Large oxygen excess in the primitive mantle could be the source of the Great Oxygenation Event. Geochemical Perspectives Letters, 5–10. https://doi.org/10.7185/geochemlet.1801

The Proterozoic Eon witnessed the emergence of eukaryotic cells, which are more complex than prokaryotic cells and contain membrane-bound organelles.

The first evidence of multicellular life appears in the fossil record during the Proterozoic Eon, including the Ediacara biota, which represents some of the earliest known complex organisms.

The Rodinia supercontinent formed and broke apart during the Proterozoic Eon, influencing global tectonic and climatic patterns.

Stromatolites, layered structures formed by the growth of cyanobacteria, are abundant in Proterozoic sedimentary rocks and provide valuable clues about early life on Earth.

The Proterozoic Eon laid the groundwork for the subsequent explosion of biodiversity during the Phanerozoic Eon, which includes the evolution of complex animals and plants.