How Old Are They?
The engravings cannot be dated directly with current archaeological techniques, necessitating the use of indirect dating techniques.
The Aboriginal Australians arrived in the North of Australia around 50000 years ago, but the earliest evidence of occupation in the Sydney region is dated to about 10000 BC, in the Bidjigal Reserve in the Hills District of North-West Sydney. However, dates of over 20000 years have been found in the Blue Mountains, and so it is reasonable to suppose that Aboriginal people may have been in the Sydney region around then, although their settlements have not yet been discovered.
The Sydney engravings are of a style known as "simple figurative", which conventional archaeology dates to the last 5000 years. Other engravings show European sailing ships, and so cannot be more than about 200 years old. The dates therefore range from 5000 to 200 years ago. It is likely that some of the freshest engravings represent the later part of that time range, whilst the most worn represent the earliest part. However, the situation is complicated by the fact that the engravings were sometimes "re-grooved" during ceremonies.
It has been claimed that some engravings appear to show Thylacines and other mammals which have been extinct in the Sydney region for many thousands of years, and so are presumably that old. In support of this, it is certainly true that rock art elsewhere (e.g. Kakadu National Park) does show extinct animals, and so must be tens of thousands of years old. However, at the moment there is no hard evidence to support these claims for Sydney rock art.
Read more about this topic: Sydney Rock Engravings