The Law of biogenesis says that life only comes from life (in Latin: Omne vivum ex vivo).
As long ago as ancient Greece, people believed that small creatures spontaneously appeared, such as mice appearing from grain, or maggots from rotting meat. However, in 1668 Francesco Redi conducted experiments showing that maggots came from eggs laid on the meat by flies.
Nevertheless, many people continued to believe that microorganisms, such as microbes, spontaneously generated. This idea was put to rest with experiments done by Louis Pasteur in 1864, and the law of biogenesis was born.
This law is put to the test every day, in the food preservation industry. Food that is to be kept in good condition for an extended period of time is sealed in cans, bottles, or other containers, and sterilised to kill any organisms that might be in it. Because all life in the container has been killed, and because the container is sealed to prevent any microorganisms getting in, the food is kept in good condition. The law is accepted so thoroughly that if a container is found to contain living organisms, investigators will look for a hole in the container, a failure to properly sterilise the food, or tampering. They never conclude that the life in the container arose spontaneously.
Despite this law, many scientists believe that the first life arose from non-living matter. In proposing this, they speculate that although life has never been observed to spontaneously arise, it must have at some time in the past. Being a unique past event, the speculation cannot be tested or refuted, thus remaining an article of blind faith for those who reject the idea that life was created.