Final answer:
Mass extinctions clear ecological niches that lead to adaptive radiation, allowing new species to thrive and fill various roles in the ecosystem. The Permian extinction and the extinction 65 million years ago led to the rise of dinosaurs and mammals, respectively. The Cambrian explosion was also a period of rapid speciation and diversity.
Step-by-step explanation:
Mass extinctions have had a significant impact on life's history on Earth by removing a substantial number of species and, consequently, opening up vast new habitats for adaptive radiation. When such cataclysmic events occur, like volcanic eruptions or meteor strikes, they may result in a period of mass extinction, erasing some genetic lines and creating room for those surviving to evolve and fill the newly emptied ecological niches.
One example of this is the extinction at the end of the Permian period, which led to the rise of dinosaurs in the Mesozoic Era. Likewise, the extinction 65 million years ago paved the way for mammals to become dominant. Such periods of mass extinction show that neither terrestrial nor marine biotas are infinitely resilient but can recover through evolutionary bursts of speciation. An ideal example of adaptive radiation can be observed in the Hawaiian Islands, where geographical isolation has led to multiple new species evolving from a single founder species, like the Hawaiian honeycreeper.
The Cambrian explosion, another historical event, is noted for the appearance of many new types of organisms, indicative of a major adaptive radiation event.