Rock dating methods
The first 2 are subject to considerable error and should only be used when ultrasonography facilities are not available.
The date of feeling the first fetal movements (quickening) is far too unreliable to be useful.
It wasn't until well into the 20th century that enough information had accumulated about the rate of radioactive decay that the age of rocks and fossils in number of years could be determined through radiometric age dating.
William Smith was one of the most important scientists from this time who helped to develop knowledge of the succession of different fossils by studying their distribution through the sequence of sedimentary rocks in southern England.
One of the most intriguing and perplexing legends of the Australian Aboriginal people is that of the Wandjinas, the supreme spirit beings and creators of the land and people.
The land of the Wandjina is a vast area of about 200,000 square kilometres of lands, waters, sea and islands in the Kimberley region of north-western Australia with continuous culture dating back at least 60,000 years but probably much older.
The date of the first documented positive pregnancy test and the beta-human chorionic gonadotropin (b HCG) level may help ascertain the minimum gestational age.
In women who conceived following assisted reproduction techniques, the date of embryo transfer is known and may date the pregnancy accurately.