Sometimes extinction can be a blessing. Aren't you glad this 500-million-year-old "walking cactus," for example, isn't alive today? It lived on the bottom of the ocean, to be fair. But just knowing it was there would have bothered me.
Conservationists have been speculating for years that we're in the midst of a mass extinction. In the planet's history, five of these events have occurred. To qualify, three-quarters of all species on Earth must be wiped out. The most recent mass extinction was the one that did in the dinosaurs. Prior to that, incidents such as global cooling or global warming served to wipe out huge numbers of species. And before any of those events, when the planet was occupied by simple single-celled creatures, the rise of the first photosynthesizers released oxygen into the atmosphere and destroyed most other forms of life.
So Earth is no stranger to slate-wiping events. But ...
