The population of earth continues to grow at a fast pace. Since the creation of man around 3984 B.C. it took about 5,800 years for the world's total number of people to reach one billion. It took one hundred and ten years after reaching this landmark for the population to reach two billion in 1930 A.D. It took only another thirty years for the number of humans to reach three billion. In 1974, only fourteen years later, the globe's number of human beings stood at four billion. The five billion mark took another thirteen years to reach. The number of humans then climbed to six billion in 1999 and, as of July 2013, stands at an estimated 7.1 billion. Roughly 46% of the current population is considered part of the global labor force.
The legal systems of nearly all countries on earth generally fall into one of five main categories.
Civil Law, which is any legal system based on the Roman system
Common Law, which is a set of rules based on judicial decisions and custom. Common law is a part of the legal system in the United States. One example of common law can be found in regard to who is considered legally married. In most (if not all) U.S. states a couple is considered legally married if, in spite of not having a valid marriage certificate, they have lived together for a certain set number of years.
Customary law, which is based on an established pattern of behavior that is objectively verifiable within a particular social setting.
Mixed law, which is a system that is a mix of other legal systems (e.g. Civil and common law)
Religious law, which is a system based on religious beliefs. For example, Iran is a country which is governed by a religious legal system based on sharia (Islamic) law.