I hear this story from one of my friends:

> Blue-green algae can convert carbon dioxide into oxygen through
> photosynthesis, so the concentration of oxygen in the atmosphere kept
> going up over a long period after their appearance. Finally, those
> oxygen poisoned blue-green algae through some mechanism, which
> effectively killed many of them. As a side effect, the oxygen produced
> lead to the evolution of fishes and other fantastic creatures, including human beings.

I wonder whether it is true. After some searching, I found out that blue-green algae, like most algae, can perform photosynthesis. However, I can't tell whether oxygen is poisonous to blue-green algae.