In a sense they were the only ecological disaster the planet had ever seen. Something isn't a 'disaster' unless there's some sentient observer to judge the outc

In a sense they were the only ecological disaster the planet had ever seen. Something isn't a 'disaster' unless there's some sentient observer to judge the outcome. Asteroid strikes, volcanic eruptions, floods, gamma ray bursts, black holes... they're not disasters, just events, until someone gets upset about them.