The units commonly used for geologic age are mega-annum (Ma) for millions of years, giga-annum (Ga) for billions of years, and kiloannum (ka) ka for thousands of years.Because these units are used according to the rules of the metric system, the M in Ma and the G in Ga must be capitalized, and the k in ka must not be capitalized.The combination of these two types of geologic ages makes a complete record of earth's geologic history in terms of the order of events and in terms of how many years ago each event occurred.Relative geologic age refers to the order in which geologic events occurred.Absolute geologic age refers to how long ago a geologic event occurred or a rock formed, in numeric terms, such as 65.5 million years ago.Some rocks and minerals can have their absolute age directly measured by analyzing the ratios of certain radioactive and non-radioactive isotopes they contain.
adaptive landscape: A graph of the average fitness of a population in relation to the frequencies of genotypes in it.
These people will have dates on a regular basis, and they may or may not be having sexual relations.
This period of courtship is sometimes seen as a precursor to engagement or marriage.
Dating as an institution is a relatively recent phenomenon which has mainly emerged in the last few centuries.
From the standpoint of anthropology and sociology, dating is linked with other institutions such as marriage and the family which have also been changing rapidly and which have been subject to many forces, including advances in technology and medicine.