They used pottery and other materials in sites to date 'relatively'.
They thought that sites which had the same kinds of pots and tools would be the same age.
Rasmus Nyerup's quote reminds us of the tremendous scientific advances which have taken place in the 20th century.
In Nyerup's time, archaeologists could date the past only by using recorded histories, which in Europe were based mainly on the Egyptian calendar.
Obviously, this works only for things which were once living.
Clearly, such huge time periods cannot be fitted into the Bible without compromising what the Bible says about the goodness of God and the origin of sin, death and suffering—the reason Jesus came into the world (See Six Days? He said, This only makes sense with a time-line beginning with the creation week thousands of years ago.
It makes no sense at all if man appeared at the end of billions of years.
Geologists draw on it and other basic principles ( to determine the relative ages of rocks or features such as faults.
Relative age dating also means paying attention to crosscutting relationships.