1) How are the moon’s craters evidence that large meteoroids probably hit Earth?

2) Why is evidence of meteoroid impact rare on Earth, despite the fact that meteoroids often pass into Earth’s atmosphere?

3) About what age are the rocks that show the highest level of iridium?

4) What are two possible sources for the high iridium level shown in the graph?

5) In several other parts of the world, rocks of the same age have similar levels of iridium. What can you infer from this information?