How did the atmosphere and tectonic conditions change during the Proterozoic Eon?

The Proterozoic Eon is a geological time period that covers around 2 billion years, from 2.5 billion years ago (Ga) to 541 million years ago (Ma). It follows the Archean Eon and precedes the Phanerozoic Eon, where the current era, the Cenozoic, is situated. The Proterozoic Eon is subdivided into three eras: Paleoproterozoic (2.5-1.6 Ga), Mesoproterozoic (1.6-1.0 Ga), and Neoproterozoic (1.0-0.541 Ga). This Eon is characterized by significant changes in Earth's atmosphere, tectonic processes, and the emergence of complex life forms.

At the beginning of the Proterozoic Eon, the Earth's atmosphere was composed mostly of methane (CH₄) and ammonia (NH₃), with very low levels of oxygen. This early Earth atmosphere was highly reducing. 1. The Great Oxidation Event (GOE): Around 2.4 Ga, the first oxygen-producing photosynthetic organisms, known as cyanobacteria, evolved. This led to a gradual increase in atmospheric oxygen levels, causing the "Great Oxidation Event" (GOE). This event resulted in profound changes to Earth’s biogeochemical cycles and an increase in free oxygen in the atmosphere. 2. Oxygen levels stabilization: After the GOE, oxygen levels in the atmosphere gradually stabilized, reaching around 1-10% of modern atmospheric levels. The increase in oxygen led to the formation of an ozone layer, which protected life on Earth from harmful ultraviolet (UV) radiation. 3. Snowball Earth events: In the Neoproterozoic Era (1.0-0.541 Ga), the Earth went through two significant glaciation events known as "Snowball Earth," caused by severe cooling and global ice cover. These events may have affected atmospheric changes and led to the fluctuation of greenhouse gases, such as carbon dioxide (CO₂).

The Proterozoic Eon experienced substantial changes in tectonic activity, shaping Earth’s crust and influencing life's development. 1. Emergence of stable continental crust: During the Paleoproterozoic Era, the first stable continental crusts began to form through processes like accretion, subduction, and the collision of microcontinents. The formation of these crusts allowed the development of complex life and ecosystems. 2. Assembly and breakup of supercontinents: Throughout the Proterozoic Eon, supercontinents began to assemble and break apart, influencing global climate and sea levels. The first supercontinent, Columbia (also known as Nuna), was formed around 1.8 Ga and began to break up around 1.5 Ga. Rodinia, the second supercontinent, was assembled around 1.25 Ga and broke apart around 0.75 Ga.

The changes in the atmosphere and tectonic conditions during the Proterozoic Eon led to an increase in the complexity of life forms on Earth. 1. Emergence of eukaryotes: The increased oxygen levels and protective ozone layer allowed for the development of eukaryotes, complex cells with a nucleus, during the Mesoproterozoic Era (1.6-1.0 Ga). 2. Multicellular life: In the Neoproterozoic Era, the first multicellular organisms began to form due to increased access to oxygen and nutrients. In summary, the Proterozoic Eon experienced significant changes in Earth's atmosphere, including the Great Oxidation Event, the stabilization of oxygen levels, and glaciation events. The development of tectonic processes led to the formation of stable continental crusts and the assembly of supercontinents. These changes laid the foundation for more complex life forms, allowing for the emergence of eukaryotes and multicellular organisms.