the prevalence of what mostly isotopic and radioactive element in a layer of soil from 65 - 66 million years…

the prevalence of what mostly isotopic and radioactive element in a layer of soil from 65 - 66 million years ago indicates that the dinosaurs were killed by an asteroid in the k - t event?\niridium\nazimuth\nboron\ncadmium
Answer
Brief Explanations:
The high - concentration of iridium in the 65 - 66 million - year - old soil layer is evidence for the asteroid impact theory of dinosaur extinction. Iridium is rare on Earth's surface but abundant in asteroids. Azimuth is a direction - related term, not an element. Boron and cadmium are not associated with this event in this context.
Answer:
Iridium