Final answer:
The K-Pg mass extinction is attributed to an asteroid impact, evidenced by high concentrations of iridium and the Chicxulub crater. This event led to the blocking of sunlight, which disrupted photosynthesis and affected the entire food chain.
Step-by-step explanation:
The Cretaceous-Paleogene (K-Pg) mass extinction, which occurred around 66 million years ago, is most famously attributed to the impact of an asteroid. This event is supported by evidence such as the presence of a high concentration of the element iridium, which is rare on Earth but common in asteroids, in the geological layer marking the K-Pg boundary. Moreover, the discovery of the Chicxulub crater in Yucatan, Mexico, provided a strong case for a catastrophic impact event.
The aftermath of the asteroid impact is believed to have included massive dust clouds that blocked sunlight, leading to a major disruption in Earth's climate and a significant drop in photosynthesis. This would have been detrimental to plant and algae life, and consequently, the entire food chain. Alongside this, it is suggested that the impact caused wildfires, acid rain, and even a 'nuclear winter' effect that would have cooled the planet.
Other major mass extinctions in Earth's history, like the Permian mass extinction, might have involved massive volcanic activity, which could have also contributed to atmospheric changes and global cooling. However, for the K-Pg event, the asteroid impact theory remains the most substantiated by current scientific evidence.