| Name | Mesoproteric Era |
| Key Events | Rise of complex multicellular eukaryotes • Emergence and diversification of early plants, animals, and fungi in aquatic ecosystems • Major mass extinction event around 1.9 billion years ago • Establishment of first continental landmasses • Colonization of land by primitive plant-like organisms |
| Time Period | 2.1 to 1.8 billion years ago |
| Significance | Laid the foundations for the rise of more advanced life in the later Phanerozoic Eon |
The Mesoproteric Era, also known as the Middle Proteric, was a geologic period lasting from approximately 2.1 billion years ago to 1.8 billion years ago in this alternate timeline. It followed the earlier Paleoproteric Era and was marked by the rise and diversification of complex multicellular eukaryotic life, as well as major changes to the planet's atmosphere, oceans, and landmasses.
The Mesoproteric is defined by the first appearance and rapid evolution of eukaryotic organisms - cells with a true nucleus and membrane-bound organelles. This represented a major step forward in complexity from the earlier dominance of prokaryotic lifeforms like bacteria and archaea.
The earliest known eukaryotes emerged around 2.1 billion years ago, likely evolving from symbiotic communities of prokaryotic cells. These primordial eukaryotes included the ancestors of plants, animals, fungi, and various other single-celled organisms. They quickly diversified into a wide range of new lifeforms, filling a variety of aquatic ecological niches.
The Mesoproteric world was dominated by complex, multilayered aquatic ecosystems in the planet's seas and oceans. Primitive plants, such as algae, seaweed, and phytoplankton, formed the basis of these food webs, providing energy through photosynthesis. Heterotrophic organisms like primitive sponges, jellyfish-like animals, and primitive fungi then fed on the plant life and each other.
Compared to the simpler microbial communities of the Paleoproteric, these Mesoproteric ecosystems exhibited a greater diversity of lifeforms, more intricate food chains, and more sophisticated behaviors and structures. Fossil evidence shows the existence of the first known animals, which were likely simple filter-feeders and predators.
Around 1.9 billion years ago, the Mesoproteric experienced a major global mass extinction event that reshaped life on Earth. The causes are still debated, but may have included rapid climate changes, volcanic activity, or the exhaustion of key nutrients in the oceans.
This mass extinction wiped out a significant portion of the eukaryotic life that had emerged and diversified during the earlier Mesoproteric. However, it also opened up new ecological niches that allowed surviving organisms to rapidly evolve and repopulate the biosphere. The aftermath of this event set the stage for the rise of more complex and advanced lifeforms in the later Neoproterozoic Era.
As the Mesoproteric progressed, the planet's continental landmasses also began to take shape. Shallow coastal areas and tidal zones saw the first tentative colonization attempts by primitive plant-like organisms, marking the very beginnings of life on land.
These earliest terrestrial lifeforms were simple, nonvascular plants that reproduced via spores. They likely evolved from aquatic algae that had adapted to the harsher conditions of the shoreline. While still dependent on water for reproduction, these proto-plants helped establish the foundations for the later rise of more complex land-dwelling flora and fauna.
Overall, the Mesoproteric was a critical transitional period that laid the groundwork for the stunning diversity of life that would emerge in the eons to come. The rise of eukaryotes and the first aquatic ecosystems set the stage for the planet's biosphere to evolve in new and complex directions.
