His observations may well show earth-shattering results (12)
I believe the answer is:
seismologist
'his observations may well show earth-shattering results' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
This is the entire clue.
Can you help me to learn more?
(Other definitions for seismologist that I've seen before include "one could sense the shock waves" , "Earthquake scientist" , "One who studies earthquakes" .)