The origin of life is a scientific problem which is not yet solved. There are plenty of ideas, but few clear facts.[1]
It is generally agreed that all life today evolved by common descent from a single primitive lifeform.[2] We do not know how this early form came about, but scientists think it was a natural process which took place perhaps 3,900 million years ago. This is in accord with a philosophy called naturalism: only natural causes are admitted.
We do not know whether metabolism or genetics came first. The main hypothesis which supports genetics first is RNA world hypothesis, and the one which supports metabolism first is Protein world hypothesis.
Another big problem is how cells develop. All existing forms of life are built out of cells.[3]
The Nobel Prize in Chemistry winner Melvin Calvin wrote a book on the subject,[4] and so did Alexander Oparin.[5] What links most of the early work on the origin of life was the idea that before biological evolution began there must have been a process of chemical evolution.[6] Another question which has been discussed by J.D. Bernal and others is the origin of the cell membrane. By concentrating the chemicals in one place, the cell membrane performs a vital function.[7]
Many religions teach that life did not evolve spontaneously, but was deliberately created by a god. Such theories are a part of creationism. If they claim this happened within the last few thousand years, this is much more recent than the fossil record suggests. The lack of evidence for such views means that most scientists do not believe them.
