What major biological events occurred near the end of Proterozoic time?

The Proterozoic time period is a geological eon that lasted from approximately 2.5 billion years ago to 541 million years ago. It is subdivided into three eras: the Paleoproterozoic, the Mesoproterozoic, and the Neoproterozoic. During this eon, the Earth's environment was largely stable, and it was marked by the development of early life forms.

One of the major biological events that happened during the Proterozoic time period was the Great Oxygenation Event (GOE), also known as the Great Oxidation or the Oxygen Catastrophe. This event took place around 2.4 billion years ago during the Paleoproterozoic era. The GOE was marked by the appearance and rapid increase of oxygen in Earth's atmosphere due to the proliferation of cyanobacteria. These bacteria were photosynthesizing, producing oxygen as a by-product. The oxygenation of the atmosphere had profound impacts on existing life forms and laid the foundation for more complex life forms to evolve.

The development of eukaryotic cells was another significant biological event that occurred during the Proterozoic time period. Eukaryotic cells are more complex than the earlier prokaryotic cells, as they contain membrane-bound organelles and a nucleus. The first eukaryotic cells likely originated around 2 billion years ago. The development of eukaryotic cells allowed for greater diversity in life forms and ultimately led to the evolution of multicellular organisms.

The emergence of multicellular life forms during the Proterozoic time period marks one of the most crucial biological events in Earth's history. The earliest multicellular organisms, called the Ediacaran biota, first appeared around 635 million years ago during the Neoproterozoic era. The Ediacaran biota included various types of algae, simple invertebrates, and other soft-bodied organisms. Their appearance laid the groundwork for the eventual diversification of life during the Cambrian Explosion.

Two significant Ice Age events (global glaciations) called Snowball Earth events also took place during the Proterozoic time period, with the most recent one ending around 635 million years ago, shortly before the emergence of the Ediacaran biota. These events led to drastic changes in Earth's environment, including a decrease in global temperatures and oceanic oxygen levels. The recovery from these glaciations might have played a vital role in creating conditions suitable for the evolution and diversification of multicellular life. In summary, the major biological events that occurred towards the end of the Proterozoic time period include the oxygenation of the atmosphere, development of eukaryotic cells, emergence of multicellular life, and recovery from the Snowball Earth events, all of which contributed to the evolution and diversity of life on our planet.