“It is no valid objection that science as yet throws no light on the far higher problem of the essence or origin of life” (Darwin, Charles. The Origin of Species. 6th edition, 1882. p. 421
however, Over the time frame from the late Hadean to the present, this becomes sufficient to explain both the diversity within and similarities between the forms of life observed on earth, including both living forms directly observed in the present, and extinct form indirectly observed from the fossil record.