Final answer:
Eukaryotic organisms evolved after global glaciation thanks to innovations like sexual reproduction and cell specialization, along with the endosymbiotic event that created complex cell structures. This paved the way for the Cambrian explosion after the Precambrian Extinction.
Step-by-step explanation:
Eukaryotic organisms were able to evolve after global glaciation due to a series of adaptations that conferred advantages in the changing environmental conditions. For example, sexual reproduction increased genetic diversity and the chances of survival through changing environments, which sped up evolutionary processes. Additionally, the development of cell specialization within colonies led to more efficient systems and ultimately to the rise of multicellular organisms. Endosymbiotic theory further explains the evolution of eukaryotic cells from the symbiotic relationship between an Archaea and a Bacterium, where organelles such as mitochondria and chloroplasts evolved. The genomic fusion model, though still debated, supports the notion of eukaryotic cells originating from a merging of genes from these two distinct prokaryotic lineages.
Following the Precambrian Extinction, the stage was set for a diverse array of life, also known as the Cambrian explosion, in which eukaryotic life forms diversified significantly. The origins of eukaryotes are linked to Archaea biochemically, but our organelles suggest a descent from bacterial endosymbiosis. The fossil record, though incomplete, hints at eukaryotes emerging around 2 billion years ago, with subsequent diversification leading to the establishment of major eukaryotic clades.