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.
Proponents of evolution publicize radioisotope dating as a reliable and consistent method for obtaining absolute ages of rocks and the age of the earth.
This apparent consistency in textbooks and the media has convinced many Christians to accept an old earth (4.6 billion years old).
Since there doesn't seem to be any systematic error that could cause so many methods to agree with each other so often, it seems that there is no other rational conclusion than to accept these dates as accurate.
However, this causes a problem for those who believe based on the Bible that life has only existed on the earth for a few thousand years, since fossils are found in rocks that are dated to be over 500 million years old by radiometric methods, and some fossils are found in rocks that are dated to be billions of years old.
In a related article on geologic ages (Ages), we presented a chart with the various geologic eras and their ages.
In a separate article (Radiometric dating), we sketched in some technical detail how these dates are calculated using radiometric dating techniques.
We are told that these methods are accurate to a few percent, and that there are many different methods.The latest high-tech equipment permits reliable results to be obtained even with microscopic samples.Radiometric dating is self-checking, because the data (after certain preliminary calculations are made) are fitted to a straight line (an "isochron") by means of standard linear regression methods of statistics.For example, uranium will radioactively decay through a series of steps until it becomes the stable element lead. The original element is referred to as the parent element (in these cases uranium and potassium), and the end result is called the daughter element (lead and argon).The straightforward reading of Scripture reveals that the days of creation () were literal days and that the earth is just thousands of years old and not billions.Here is one example of an isochron, based on measurements of basaltic meteorites (in this case the resulting date is 4.4 billion years) [Basaltic1981, pg. Skeptics of old-earth geology make great hay of these examples.