Final answer:
Humans and cyanobacteria have both significantly impacted the Earth's environment. Cyanobacteria's role in the Great Oxygenation Event altered the composition of the atmosphere and enabled the evolution of complex life, while humans have dramatically transformed the planet, particularly in the post-industrial era.
Step-by-step explanation:
Indeed, humans have profoundly impacted the Earth, but we are not the first species to have done so. The Great Oxygenation Event (GOE), initiated by cyanobacteria, radically transformed the Earth's atmosphere and the course of life itself. Approximately 2.5 billion years ago, cyanobacteria began producing oxygen through photosynthesis, leading to the accumulation of oxygen in the atmosphere. This event caused the first-known mass extinction, as the anaerobic organisms at the time could not survive in the newly oxygenated environment. However, the rise of oxygen also paved the way for multicellular lifeforms and allowed for more complex life to evolve.
Another species that significantly changed the Earth is plants. Their evolution and the spread across landmasses changed the atmospheric composition, contributed to soil formation, and created habitats for numerous other species. Lastly, events like the asteroid impact that occurred 65 million years ago also had a profound impact, leading to the extinction of the dinosaurs and many other species, which allowed mammals, including humans, to dominate.