Final answer:
The Moon's geological features' relative ages were identified after Apollo astronauts brought back lunar rocks for radioactive age-dating, confirming that the Moon is an ancient surface, with the oldest rocks dating from 3.3 to 4.4 billion years.
Step-by-step explanation:
The relative ages of geological features on the moon can be determined using radioactive age-dating techniques. These methods became reliable once lunar samples were brought back to Earth by Apollo astronauts.
The dating of these samples revealed that much of the Moon's crust consists of silicate rocks known as anorthosites and that the solidification ages of the sampled rocks ranged from about 3.3 to 4.4 billion years old. Identifying the relative ages involves examining features such as the density of cratering; heavily cratered regions like the lunar highlands are older than the darker, less-cratered lava plains.
Most notably, the Apollo samples confirmed that the Moon does not have active geology like Earth and that its surface is ancient, with Earth and the Moon having been formed about 4.5 billion years ago.