Final answer:
The clay layer evidence from the Mesozoic Era's end is linked to a mass extinction caused by an asteroid impact event, supported by high iridium levels, and extensive volcanic eruptions leading to climate change.
Step-by-step explanation:
The evidence from the clay layer deposited at the end of the Mesozoic Era, particularly the Cretaceous-Paleogene boundary, is indicative of a mass extinction event.
This layer contains a higher concentration of iridium, an element more common in asteroids than in the Earth's crust, which supports the impact event theory.
The so-called Chicxulub crater in Yucatan and the abundance of shocked quartz and microtektites are further testimonies to a massive asteroid collision. In addition to this extraterrestrial event, the end of the Cretaceous is also marked by extensive volcanic eruptions known as the Deccan Traps. The eruptions released large amounts of volcanic gases, including sulphur dioxide, leading to significant climate change, which may have furthered the mass extinction.