Final answer:
Temperatures in the Cenozoic period changed, and scientists used methods like measuring greenhouse gases in the atmosphere and examining tree rings to track these changes.
Step-by-step explanation:
Scientists know that temperatures changed over the Cenozoic period through various methods and proxies. One way is by measuring greenhouse gases present in the current atmosphere, as they can indicate temperature changes. Another method is examining the number of annual rings in trees, which can provide clues about climactic changes over time.