Maybe that's misleading. The greatest catastrophe for life on Earth was when the first organisms discovered how to inhale sunlight and exhale Oxygen. Turned out Oxygen was deadly to the life forms of the day, just as some of Humanity's byproducts are deadly to the life forms of our day.
I don't know if it was lethal to all life. Perhaps it was even lethal to those first Oxygen-producers. However, from the point of view of the sum total of that day's Life, it was a disaster.
Gaia took it in stride. In fact, it was the beginning of something wonderful for Gaia, allowing Em to become fully self-regulating.
Chances are, Gaia will be just as cool with the pitiful changes Humanity is wreaking in the biosphere. As humans, we should nonetheless remember that the advent of free Oxygen spelled doom for at least the majority of the life forms of that day, and by inference our petty meddling could well spell the doom of Humanity, leaving Gaia changed, perhaps, but just as healthy as before.