> A billion years! Why did it take so long to form a eukaryote then? It's because it's very x 10^9 unlikely to happen. You say it was change. Could have as wel

> A billion years! Why did it take so long to form a eukaryote then? It's because it's very x 10^9 unlikely to happen. You say it was change. Could have as well taken 0.5 or 2 billion years. In another comment, /u/dnautics said it was because in the newly formed oxygen atmosphere, the mitochondria had to seek shelter inside other cells. Who knows? At least the appearances of oxygen atmosphere and eukaryotic cells happened at about the same time. https://en.wikipedia.org/wiki/Timeline_of_the_evolutionary_history_of_life https://en.wikipedia.org/wiki/Timeline_of_the_evolutionary_h...