The end Cretaceous mass extinction 65 million years ago is associated with the end of the dinosaurs. Virtually no large land animals survived. Plants were also affected and tropical marine life was decimated. At this time, the oceans flooded up to 40% of the continents. What would become us now had a chance to flourish. We were very small mammals and we had a lot of land to fill.
Of course the word 'opportunity' is, in this instance, a value-judgement. I would imagine that the organisms that were unable to adapt to the radically changing environments during past extinction waves would not have seen it as an opportune time at all. But, then, one man's death is often another man's bread, and there will always be those able to profit from even the most horrible disasters.
Mass extinctions occur when extreme temperatures happen.https://science.howstuffworks.com/life/evolution/extinction3.htm
The outcomes of each of the mass extinctions is that animal and/or bacteria die.
When there are mass extinctions they are usually followed by adaptive radiation and very rapid diversification. The last mass extinctions happened 65 million years ago.
No, they are fundamental to the process of evolution. Mass extinctions are less common.
Bad things
biospere
Ice age
Most extinctions occur as background extinctions because they are longer time periods unlike the shorter mass extinctions which there were only two in the Paleozoic era, the Ordovician mass extinction, and the Permian/Triassic extinction in which 95% of all marine animals became extinct
Adaptive Radiation
climate change
The most devastating mass extinction occurred in the Late Permian (~250 million years ago).
5 mass extinctions