Final answer:
Mass extinctions have been caused by natural events like asteroid impacts and volcanic activity; currently, human actions are driving a sixth mass extinction.
Step-by-step explanation:
Life on Earth has certainly been shaped by several mass extinctions, each caused by a variety of major environmental catastrophes. The most famous mass extinction is perhaps the one at the end of the Cretaceous period, about 65 million years ago, which was likely caused by a massive asteroid impact. This event ejected so much dust into the atmosphere that it blocked sunlight, leading to the collapse of ecosystems reliant on photosynthesis. Similarly, the Late Permian mass extinction, the most severe of all, might have been triggered by extensive volcanic activity and the subsequent climate change it brought about. It is noted that a sixth mass extinction is currently unfolding, driven not by natural events but by human activities, including habitat destruction, pollution, and climate change. These historical and ongoing extinction events emphasize the fragility of Earth's biodiversity in the face of rapid environmental alterations.